MXPA06000858A - Ablation device with spiral array ultrasound transducer - Google Patents

Abstract

The present invention relates to a device assembly and tissue ablation transducer (400) having a plurality of helical elements that can be operated out of phase to orient the acoustical energy beam forward or backward in the longitudinal direction. The transducers includes a cylindrical inner electrode (402), a cylindrical piezoelectric (403) material disposed over the inner electrode, and a cylindrical outer electrode (404) disposed over the cylindrical piezoelectric material. Spiral grooves (figure 4a) are cut through at least the outer electrode separating the transducer into a plurality of functionally discrete helical transducer segments. The helical transducer segments can be operated independent from one another. An array of intertwined helical transducers arranged linearly along a helical axis are also contemplated.

Description

For two-letter codes and other abbreviations, refer to the "Guidance Notes on Codes and Abbreviations" appeanng at the beginning-ning ofeach regular issue of the PCT Gazette.

ABLATION DEVICE WITH SPIRAL DISPOSAL ULTRASOUND TRANSDUCER TECHNICAL FIELD OF THE INVENTION The present invention relates to a surgical device. More particularly, it relates to a tissue ablation device and transducer assembly having a plurality of helical elements that can be operated out of phase to orient the acoustic energy beam forward or backward in the longitudinal direction.

BACKGROUND OF THE INVENTION Many devices and methods of local energy administration have been developed to treat various abnormal tissue conditions in the body and, particularly, to treat abnormal tissue along the walls of body space that define different body spaces in the body. For example, different devices have been described with the primary purpose of treating or recanalizing the atherosclerotic vessels with localized energy delivery. Several prior devices and methods combine energy management assemblies in conjunction with cardiovascular stent devices, in order to deliver energy locally to the tissue and maintain the evidence in affected lumens such as blood vessels. Endometriosis, another abnormal condition of wall tissue that is associated with the endometrial cavity and is characterized by a dangerously proliferative uterine wall tissue along the surface of the endometrial cavity, has also been treated with devices and methods of administration of local energy. Other devices and methods utilizing catheter-based heat sources have also been described with the intended purpose of inducing thrombosis and controlling bleeding within certain body lumens such as vessels. Some detailed examples of local energy management devices and related procedures, such as those of the types described above, are described in the following references: U.S. Patent No. 4,672,962 to Hershenson; U.S. Patent No. 4,676,258 to InoKuchi et al .; U.S. Patent No. 4,790,311 to Ruiz; U.S. Patent No. 4,807,620 to Strul et al; U.S. Patent No. 4,998,933 to Eggers et al; U.S. Patent No. 5,035,694 to Kasptzyk et al .; U.S. Patent No. 5,190,540 to Lee; U.S. Patent No. 5,226,430 to Spears et al; and U.S. Patent No. 5,292,321 to Lee; U.S. Patent No. 5,449,380 to Chin; U.S. Patent No. 5,505,730 to Edwards; U.S. Patent No. 5,558,672 to Edwards et al .; and U.S. Patent No. 5,562,720 to Stern et al .; U.S. Patent No. 4,449,528 to Auth et al .; U.S. Patent No. 4,522,205 to Taylor et al .; and U.S. Patent No. 4,662,368 to Hussein et al .; U.S. Patent No. 5,078,736 to Behl; and U.S. Patent No. 5,178,618 to Kandarpa.

Other prior devices and methods electrically couple fluid with an ablation element during the administration of local energy for the treatment of abnormal tissues. Some of said devices couple the fluid with the ablation element for the main purpose of controlling the temperature of the element during the administration of energy. Other such devices couple the fluid more directly with the tissue-device interface, either as another temperature control mechanism or in certain other applications known as a vehicle or means for the administration of localized energy. Detailed examples of ablation devices that use fluid to assist electrical coupling of electrodes to tissue are described in the following references: U.S. Patent No. 5,348,554 to Imran et al .; U.S. Patent No. 5,423,811 to Imran et al .; U.S. Patent No. 5,505,730 to Edwards; U.S. Patent No. 5,545,161 to Imran et al.; U.S. Patent No. 5,558,672 to Edwards et al; U.S. Patent No. 5,569,241 to Edwards; U.S. Patent No. 5,575,788 to Baker et al .; U.S. Patent No. 5,658,278 to Imran et al .; U.S. Patent No. 5,688,267 to Panesen et al .; U.S. Patent No. 5,697,927 to Imran et al .; U.S. Patent No. 5,722,403 to McGee et al .; U.S. Patent No. 5,769,846; and PCT Patent Application Publication No. WO 97/32525 for Pomeranz et al .; and PCT Patent Application Publication No. WO 98/02201 for Pomeranz et al.

Atrial Fibrillation Cardiac arrhythmias and atrial fibrillation, in particular, continue to be common and dangerous medical conditions associated with abnormal tissue of the cardiac chamber wall and are frequently seen in elderly patients. In patients with cardiac arrhythmia, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normal conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of cardiac tissue lead aberrantly to adjacent tissue, thereby disturbing the cardiac cycle to an asynchronous heart rate. It is known that this abnormal conduction occurs in different regions of the heart, such as, for example, in the sinoatrial node (SA) region, along the conduction pathways of the atrioventricular node (AV) and the bundle of His or well in the heart muscle tissue that makes up the walls of the ventricular and atrial cardiac chambers. Cardiac arrhythmias, including atrial arrhythmia, can be of the multiple wave reentrant type, characterized by multiple asynchronous sinuosities of electrical impulses that disperse around the atrial chamber and often self-propagate. Alternatively or in addition to the reentrant multiple wave type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium operates autonomously quickly and repetitively. Cardiac arrhythmias, including atrial fibrillation, can usually be detected using the global technique of an electrocardiogram (EKG, for its acronym in English). More sensitive methods of representation of specific conduction throughout cardiac chambers have also been described, as, for example, in U.S. Patent No. 4,641, 649 to Walinsky et al. and PCT Patent Application Publication No. WO 96/32897 for Desai. A multitude of clinical conditions can result from irregular cardiac function and the resulting hemodynamic abnormalities associated with atrial fibrillation, including embolism, cardiac collapse, and other thromboembolic events. In fact, atrial fibrillation is thought to be a significant cause of cerebral embolism, where abnormal hemodynamics in the left atrium caused by movement of the fibrillatory wall precipitate thrombus formation within the atrial chamber. A thromboembolism is ultimately triggered in the left ventricle, which then pumps the embolism to the cerebral circulation where an embolism occurs. Accordingly, numerous procedures have been developed to treat atrial arrhythmias, including pharmacological, surgical and catheter ablation procedures. Several pharmacological approaches have been described for the purpose of remediating or otherwise treating atrial arrhythmias such as, for example, the approaches described in the following references: US Patent No. 4,673,563 to Berne et al .; U.S. Patent No. 4,569,801 to Molloy et al .; and "Current Management of Arrhythmias" (1991) by Hindricks et al. However, it is generally not thought that these pharmacological solutions are completely effective in many cases and are even considered, in some cases, as producers of proarrhythmia and long-term ineffectiveness. Other surgical approaches have also been developed with the intention of treating atrial fibrillation. A particular example is known as the "labyrinth procedure", as described by Cox, J.L. et al. in "The surgical treatment of atrial fibrillation, L. Summary" Thoracic and Cardiovascular Surgery 101 (3), pp. 402-405 (1991); and also Cox, J.L. in "The surgical treatment of atrial fibrillation, IV Surgical Technique" Thoracic and Cardiovascular Surgery 101 (4), pp. 584-592 (1991). In general, the "labyrinth" procedure is designed to relieve atrial arrhythmia by restoring control of the sinus node and effective atrial systole through a prescribed pattern of incisions around the tissue wall. In the early clinical experiences reported, the "labyrinth" procedure included surgical incisions in both the left and right atrial chamber. However, more recent reports predict that the "labyrinth" surgical procedure can be considerably effective when performed only in the left atrium. See Sueda et al., "Simple Left Atrial Procedure for Chronic Atrial Fibrillation Associated with Mitral Valve Disease" (1996). The "labyrinth procedure" performed in the left atrium usually includes forming vertical incisions beginning in the two upper pulmonary veins and ending in the region of the mitral valve annulus, traversing the region of the lower pulmonary veins in the path. An additional horizontal line also connects the upper ends of the two vertical incisions. Therefore, the region of the atrial wall surrounded by the pulmonary vein ostium is isolated from other atrial tissue. In this procedure, the mechanical sectioning of atrial tissue eliminates arrhythmogenic conduction from the framed region of the pulmonary veins to the rest of the atrium by creating conduction blocks within the aberrant electrical conduction pathways. Other variations or modifications of this specific pattern just described have also been described, all sharing the main purpose of isolating known or presumed regions of arrhythmogenic origin or spread along the atrial wall. Although the "labyrinth" procedure and its variations as reported by Dr. Cox and others has had some success in treating patients with atrial arrhythmia, it is considered that its highly invasive methodology does not allow it to be applied in the majority of cases. However, these procedures have provided a guiding principle that electrically isolating defective heart tissue can successfully prevent atrial arrhythmia and, in particular, atrial fibrillation caused by arrhythmogenic conduction arising from the region of the pulmonary veins. . Less invasive catheter-based approaches have been described to treat atrial fibrillation, which implement ablation of cardiac tissue to terminate arrhythmogenic conduction in the atria. Examples of such devices and methods of catheter-based treatment have generally addressed atrial segmentation with catheter-based ablation devices and methods adapted to form linear and curvilinear lesions in the tissue wall defining atrial chambers. Some specifically described approaches provide specific ablation elements that are linear along a defined length that is intended to take the tissue to create the linear lesion. Other described approaches provide molded or molded guiding covers or covers within covers, with the intended purpose of directing the ablation tip catheters towards the left posterior atrial wall, so that the ablations in sequence along the predetermined path of tissue can create the desired injury. In addition, different modalities of energy administration have been described to form atrial wall lesions, including the use of microwave energy, laser, ultrasound, thermal conduction and, more frequently, radiofrequency to create driving blocks throughout of the cardiac tissue wall. Detailed examples of ablation device assemblies and methods for creating lesions along the atrial wall are described in the following U.S. Patent references: U.S. Patent No. 4,898,591 to Jang et al.; U.S. Patent No. 5,104,393 to Isner et al .; U.S. Patent No. 5,427,119; 5,487,385 for Avitall; U.S. Patent No. 5,497,119 to Swartz et al .; U.S. Patent No. 5,545,193 to Fleischman et al .; U.S. Patent No. 5,549,661 to Kordis et al .; U.S. Patent No. 5,575,810 to Swanson et al .; U.S. Patent No. 5,564,440 to Swartz et al .; U.S. Patent No. 5,592,609 to Swanson et al .; U.S. Patent No. 5,575,766 to Swartz et al .; U.S. Patent No. 5,582,609 to Swanson; U.S. Patent No. 5,617,854 to Munsif; U.S. Patent No. 5,687,723 to Avitall; U.S. Patent No. 5,702,438 to Avitall. Other examples of such devices and methods of ablation are described in the following PCT Patent Application Publication No. WO 93/20767 for Stern et al .; WO 94/21165 for Kordis et al .; WO 96/10961 for Fleischman et al .; WO 96/26675 for Klein et al .; and WO 97/37607 for Schaer. Additional examples of such devices and methods of ablation are described in the following published articles: "Physics and Engineering of Transcatheter Tissue Ablation". Avitali et al., Journal of American College of Cardiology, Volume 22, No. 3: 921-932 (1993); and "Right and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation", Haissaguerre et al., Journal of Cardiovascular Electrophysiology 7 (12), p. 1132-1144 (1996). In addition to those known assemblies outlined above, additional assemblies of tissue ablation devices have recently been developed for the specific purpose of ensuring firm contact and conscientious positioning of a linear ablation element along a length of tissue upon anchoring the element. in at least one predetermined location along that length, as well as to form a "labyrinth" type lesion pattern in the left atrium. An example of such assemblies is that described in U.S. Patent No. 5,971, 983, issued October 26, 1999, which is incorporated herein by reference. The assembly includes an anchor in each of two ends of a linear ablation element, in order to fix those ends in each of two predetermined locations along the left atrial wall, such as the two adjacent pulmonary veins, so as to that tissue ablation can be performed along the length of tissue extending in between. In addition to attempting the segmentation of the atrial wall with larger linear lesions to treat atrial arrhythmia, other devices and methods of ablation have been described that are intended to use expandable members such as balloons to perform ablation of cardiac tissue. Some of said devices have been described primarily for use in the ablation of tissue wall regions along the cardiac chambers. Other devices and methods have been described for treating abnormal conduction of the left accessory pathways and, in particular, associated with the "Wolff-Parkinson-White" syndrome; many of these descriptions use a balloon to ablate from within a region of an associated coronary sinus adjacent to the heart tissue in which ablation is desired. Further detailed examples of devices and methods such as the types just described are described in different ways in the following published references: Fram et al., In "Feasibility of RF Powered Thermal Balloon Ablation of Atrioventricular Bypass Tracts to the Coronary Sinus : In vivo Canine Studies ", PACE, Vol. 18, p. 1518-1530 (1995); "Long-term effects of percutaneous laser balloon ablation from the canine coronary sinus", Schuger CD et al., Circulation (1992) 86: 947-954; and "Percutaneous laser balloon coagulation of accessory pathways," McMath L. P. et al., Diagn Ther Cardiovasc Interven 1991; 1425: 165-171.

Arrhythmias derived from foci in the pulmonary veins It has also been observed that different modes of atrial fibrillation are focal in nature, caused by the rapid and repetitive functioning of an isolated center within the cardiac muscle tissue associated with the atrium. These foci may act as either a paroxysmal atrial fibrillation trigger or may even maintain fibrillation. Distinct descriptions have suggested that focal atrial arrhythmia is often derived from at least one region of tissue along one or more pulmonary veins of the left atrium and, even more particularly, in the superior pulmonary veins. Less invasive techniques of catheter-based percutaneous ablation have been described using final electrode catheter designs with the intention of performing ablation and thereby treating focal arrhythmias in the pulmonary veins. These ablation procedures are typically characterized by the increasing application of electrical energy to the tissue to form focal lesions designed to terminate inappropriate arrhythmogenic conduction.

An example of a focal ablation method for treating focal arrhythmia derived from a pulmonary vein is described by Haissaguerre et al., In "Right and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation", in Journal of Cardiovascular Electrophysiology 7 (12), pp. 1132-1144 (1996). Haissaguerre et al. They describe radiofrequency catheter ablation of paroxysmal atrial fibrillation refractory to drugs using linear atrial lesions supplemented with focal ablation directed at arrhythmogenic foci in a population of monitored patients. The site of the arrhythmogenic foci was usually located just inside the superior pulmonary vein and focal ablations were usually performed using a standard 4 mm single tip ablation electrode. Another method of focal ablation to treat atrial arrhythmias is described in Jais et al., "A focal source of atrial fibrillation treated by discrete radiofrequency ablation", Circulation 95: 572-576 (1997). Jais et al. describe the treatment of patients with paroxysmal arrhythmias derived from a focal source by ablating that source. At the site of the arrhythmogenic tissue, in the left and right atria, several pulses were applied from a discrete source of radiofrequency energy in order to eliminate the fibrillation process. Other assemblies and methods that address focal sources of arrhythmia in the pulmonary veins have been described by ablating circumferential regions of tissue, either along the pulmonary vein, in the ostium of the vein along the wall atrial or around the ostium and along the atrial wall. More detailed examples of assemblies and methods of devices for treating focal arrhythmia just like those described, are described in PCT Patent Application Publication No. WO 99/02096 for Diederich et al. and also in the following pending US patent and patent applications: U.S. Patent No. 6,024,740, issued February 15, 2000 to Michael D. Lesh et al., for "Circumferential Ablation Device Assembly"; U.S. Patent No. 6,012,457, issued January 11, 2000 to Michael D. Lesh, for "Device and Method of Forming a Circumferential Conduction Block to Pulmonary Vein"; U.S. Patent No. 6,117,101, issued September 12, 2000 to Chris J. Diederich et al., For "Circumferential Ablation Device Assembly"; and US Serial No. 09 / 260,316 for "Device and Method for Forming a Circumferential Conduction Block in a Pulmonary Vein" for Michael D. Lesh. Another specific device assembly and method that is intended to treat focal atrial fibrillation by ablating a circumferential region of tissue between two seals to form a conduction block to isolate an arrhythmogenic focus within a pulmonary vein is described in the US Pat. US No. 5,938,660 and a related PCT Patent Application Publication No. WO 99/00064.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a tissue ablation device and transducer assembly having a plurality of helical elements that can be operated out of phase to orient the acoustic energy beam forward or backward in the longitudinal direction. In one embodiment of the invention, a cylindrical ultrasound transducer having an internal cylindrical electrode is provided. A cylindrical piezoelectric material is disposed along the internal electrode. A cylindrical external electrode is disposed along the cylindrical piezoelectric material, the cylindrical outer electrode having spiral notches that separate the external electrode into a plurality of discrete helical elements. In another embodiment of the invention, a cylindrical ultrasound transducer having a cylindrical internal electrode, a cylindrical piezoelectric material arranged along the internal electrode and a cylindrical external electrode arranged along the cylindrical piezoelectric material is provided. The spiral grooves are cut through the external electrode and at least a portion of the cylindrical piezoelectric material. The spiral grooves separate the transducer into a plurality of functionally discrete helical transducer segments. In another modality more, the present invention has an ablation element having a plurality of intertwined helical transducers arranged in a linear fashion along a longitudinal axis.

The present invention also contemplates an ablation element comprising an ultrasonic transducer segmented into a plurality of functionally discrete interleaved helical transducer segments disposed in a linear fashion along a longitudinal axis. In another embodiment of the present invention, an ablation catheter assembly is provided to ablate a region of tissue in a body space. The ablation catheter has an elongate delivery member that has a proximal end portion and a distal end portion. An anchor mechanism adapted to take a substantial portion of tissue in the body space engages the distal end portion of the elongated delivery member. An ablation element is attached to the distal end portion of the elongated delivery member. The ablation element has an ultrasonic transducer segmented into a plurality of functionally discrete interleaved helical transducer segments disposed in a linear fashion along a longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a perspective representation showing an example of a circular ablation pathway. Figure 1B is a perspective representation showing an example of an elliptical ablation pathway. Figure 1C is a perspective representation showing an example of an irregular ablation path. Figure 1 D is a perspective representation showing an example of a stepped ablation pathway. Figure 2A is a perspective view showing an ablation catheter operatively connected with an ablation control system and a position detection system in accordance with an embodiment of the present invention. An expandable member of the catheter is illustrated in an expanded state. Figure 2B is a perspective view showing the details of an ablation member in the expanded state at a distal end of the ablation catheter of Figure 2A in accordance with an embodiment of the present invention. Figure 3A is a cross-sectional view showing the construction of a typical cylindrical ultrasonic transducer of the prior art having internal and external electrodes. Figure 3B is a perspective view of a typical ultrasound transducer of the prior art in isolation, showing electrical conductors coupled with the transducer. Figure 3C is a perspective view of a prior art ultrasound transducer with individually controlled sectors.

Figure 3D is a side view of a prior art ablation catheter showing the collimated radial acoustic energy beam pathways when the ablation device is placed in a lumen of the body, such as a pulmonary vein. Figure 3E is a side view of a prior art ablation catheter showing the collimated radial acoustic energy beam pathways when the ablation device is placed at the junction between a body lumen and a body cavity, such as an ostium of pulmonary vein. Figure 4A is a perspective view showing the construction of a transducer sectioned into a spiral arrangement of ultrasonic transducer segments in accordance with one embodiment of the present invention. Figure 4B is a side view showing the construction of a transducer sectioned in a spiral arrangement of ultrasonic transducer segments in accordance with one embodiment of the present invention. Figure 4C is an end view showing the construction of a transducer sectioned in a spiral arrangement of ultrasonic transducer segments in accordance with one embodiment of the present invention. Figure 5A is a sectional view showing the construction of a transducer segmented by individual helical elements interleaved basically in an arrangement of segments of transducer functionally discrete in accordance with one embodiment of the present invention. Figure 5B is a close sectional view showing the construction of a transducer segmented by individual helical elements essentially interleaved in an array of functionally discrete transducer segments in accordance with one embodiment of the present invention. Figure 6A is a sectional view showing the construction of a transducer having notches extending through the external electrode and into the cylindrical piezoelectric material in accordance with one embodiment of the present invention. Figure 6B is a sectional close view showing the construction of a transducer having notches extending through the external electrode and into the cylindrical piezoelectric material in accordance with one embodiment of the present invention. Figure 7A is a schematic representation illustrating a fixed phase delay for sinusoidal input signals that control a set of transducer segments in accordance with one embodiment of the present invention. Figure 7B is a schematic representation illustrating the resulting cumulative acoustic energy beams emanating from each of the plurality of transducer elements when operated at different frequencies in accordance with one embodiment of the present invention. Figure 7C is a side view of an ablation catheter showing the acoustic energy beam paths projected at an angle relative to the longitudinal axis of the transducer when the ablation device is placed at the junction between a body lumen and a body cavity, like a pulmonary vein ostium.

DETAILED DESCRIPTION OF THE INVENTION Definition of terms The following terms have the following meanings throughout this specification. It is intended that herein the terms "body space", including derivatives thereof, mean any cavity or lumen within the body that is defined at least in part by a tissue wall. For example, the cardiac chambers, the uterus, the regions of the gastrointestinal tract and the arterial or venous vessels are considered all illustrative examples of body spaces within the intended meaning. The terms "circumference" or "circumferential", including those derived therefrom, as used herein, include a continuous path or line forming an outer perimeter or boundary that surrounds and thereby defines a region of closed space. Said continuous path begins at a location along the perimeter or external boundary and is moved along the perimeter or external boundary until it is completed at the original starting location to enclose the region of defined space. The related term "circumscribe", including derivatives thereof, as used herein, includes a surface for enclosing, enclosing or encompassing a region of defined space. Therefore, a continuous line that is drawn around a region of space and that begins and ends basically in the same location, "circumscribes" the region of space and has a "circumference" that includes the distance the line travels to. as it moves along the path that circumscribes the space. Still further, a circumferential element or path may include one or more of several shapes and may be, for example, a circular, oblong, ovular, elliptical or otherwise planar cavity. A circumferential path can also be three-dimensional, such as two semicircular paths that look in opposite directions in two different parallel or off-axis planes that are connected at their ends by line segments that create bridges between the planes. For the purpose of providing an additional illustration and example, Figures 1A-1D show the circumferential tracks 160, 162, 164 and 166, respectively. Each path 160, 162, 164, 166 is moved along a portion of a body space, for example a pulmonary vein wall, and circumscribes a region of defined space, shown at 161, 163, 165 and 167, respectively, each region of circumscribed space being a portion of the body space. However, the circumferential path does not necessarily have to be moved along a tubular structure as shown, but other geometric structures are also contemplated, such as along the atrial wall in an atrium of the heart. The term "crosscut", including derivatives thereof, as used herein, includes a way to divide or separate a region of space in isolated regions. Therefore, each of the regions circumscribed by the circumferential pathways shown in Figures 1A-1 D transversally cuts the respective body space, for example the pulmonary vein, including its lumen and its wall, to the extent that the body space respective is divided into a first longitudinal region located on one side of the cross-sectional region, which is shown, for example, in the region "X" of figure 1A, as well as a second longitudinal region on the other side of the plane of cross section, which is shown, for example, in the "Y" region, also in Figure 1A. Similarly, a circumferential pathway along other structures, such as the atrial wall around the pulmonary vein ostium, will cut transversely the pulmonary vein from the atrium. Therefore, a "circumferential driving block" according to the present invention is formed along a region of tissue that follows a circumferential path, circumscribing the tissue region and transversally cutting the tissue region with respect to electrical conduction along the circumferential path. By way of example, therefore, the transverse circumferential conduction block isolates the electrical conduction between the left atrium and a pulmonary vein. It is intended that hereinafter the terms "perform ablation" or "ablation", including derivatives thereof, include substantial alteration of the mechanical, electrical, chemical or other structural nature of the tissue. In the context of the ablation applications shown and described with respect to the variations of the illustrative device presented below, it is intended that "ablation" include a sufficient alteration of the properties of the tissue to substantially block the conduction of electrical signals from or through the heart tissue where the ablation is performed. It is intended that herein the term "element" within the context of "ablation element" includes a discrete element, such as an ultrasonic transducer, or a plurality of discrete elements, such as a plurality of separate ultrasonic transducers, which are positioned in such an so that they jointly perform the ablation of a tissue region. Therefore, an "ablation element" in accordance with the defined terms may include a whole series of specific structures adapted to ablate a defined tissue region. For example, a suitable ablation element may be formed for use in the present invention, in accordance with the teachings of the embodiments presented below, from a type of "energy emitting" structure that is adapted to emit sufficient energy as to perform tissue ablation when coupled with and energized by means of an energy source. Therefore, another particular "energy-emitting" ablation element suitable for use in the present invention may include, for example, an ultrasonic element such as an ultrasound crystal element that is adapted to emit sufficient ultrasonic sound waves to perform the tissue ablation when coupled with a suitable excitation source.

Modes of the invention The following describes ablation devices of a medical device system. The described devices may include a position monitoring system that allows a clinician to accurately locate a distal end of the medical device within a body space, using feedback information provided by the system. Said feedback information is indicative of the position of the distal end of the medical device within the body space. The following devices of the position monitoring system are particularly well suited to applications involving positioning an ablation member in an area where a pulmonary vein extends from a left atrium and with respect to a circumferential region of target tissue within the area and , therefore, these devices are described in this context. However, various aspects of the present invention can be easily adapted by the person skilled in the art for applications involving the positioning of medical articles within other body spaces. In the context of illustrative application, therapies for catheter-based cardiac arrhythmia generally involve the introduction of an ablation catheter into a cardiac chamber, such as in a percutaneous transluminal procedure, wherein an ablation element at the end portion The distal catheter is positioned at or adjacent to the aberrant conductive tissue. The ablation element is used to ablate the target tissue, thus creating an injury. Figure 2A shows an exemplary ablation catheter assembly 100 operatively connected through an electrical connector 112 with an ablation control system 118. The catheter assembly 100 includes an elongate delivery member 102 with a proximal end portion 104. and a distal end portion 106. The distal end portion 106 supports an ablation member 128 that includes an ablation element 120 and an anchor mechanism 108. In a preferred embodiment (illustrated in Figure 2A), the anchor mechanism 108 is an expandable member. The expandable member may also include a sensor 109 which is explained below. The administration member 102 desirably includes a plurality of lumens (some of which are illustrated in Figure 2B). Different wires and electrical conductors are directed to the distal end portion 106 through at least part of these lumens. In a preferred device, these lumens generally run the length of the administration member 102. However, for some applications, the lumens may be shorter. In one exam a guidewire 110 runs along a lumen in the administration member 102 from the proximal end portion 104 to the distal end portion 106. The proximal end portion 104 is also connected, through a tube 113, with a screw connector 114. By introducing fluid into the tube 113 through the screw connector 114, a physician can inflate the expandable member 108, as is known in the art. In some modes of the catheter assembly, as seen in Figure 2B, the administration member 102 includes a distal port 121, which is distal with respect to an ablation member 128. In addition, there is a proximal port 122, which is provided next to the ablation member 128. The proximal port 122 is connected to a proximal port lumen 123, while the distal port 121 is connected to a distal port lumen 124. The distal port 121 allows the clinician to introduce fluids in the patient, take fluid sam from the patient and take the fluid pressure reading on the distal side of the ablation member 128. Similarly, the proximal port 122 allows the clinician to introduce fluids into the patient, take sam of fluid from the patient and take the reading of the fluid pressure on the proximal side of the ablation member 128. These ports 121, 122 and lumens 123 and 124 are particularly useful when employing X-ray or pressure positioning techniques, as explained below. However, the catheter assembly 100 does not require including said ports and lumens when only a Doppler or A mode position monitoring system is used with the catheter assembly. In the illustrated device, the administration member 102 also includes a guide wire lumen 125 whose size allows the guidewire 110 to be followed. The lumen 125 terminates in the distal port 127 located at the distal end 106 of the administration member 102. When the constructed for use in transeptal left atrial ablation procedures, the administration member 102 desirably has an outer diameter within the range of about 1.65 millimeters and about 3.3 millimeters, and, more preferably, about 2.31 millimeters and about 2.97 millimeters. Preferably, the lumen of the guidewire 125 is adapted to slidably receive guidewires within the range of about 0.0254 centimeters to about 0.09652 centimeters in diameter and, more preferably, is adapted to be used with guide wires within the scale of approximately 0.04572 centimeters to approximately 0.0889 centimeters in diameter. When a 0.0889 centimeter guidewire should be employed, the lumen of the guide wire 125 preferably has an internal diameter of 0.1016 centimeters to approximately 0.10668 centimeters. Further, when the administration member 102 includes an inflation lumen 130 for use with an inflatable balloon (a preferred form of the expandable member 108), the inflation lumen 130 preferably has an internal diameter of approximately 0.0508 centimeters, with the so as to allow rapid deflation times, although this may vary based on the viscosity of the inflation medium used, the length of lumen 130 and other dynamic factors related to fluid pressure and flow. In addition to providing the required lumens and support for the ablation member 128, the administration member 102 for the illustrative application is also adapted to be inserted into the left atrium, so that the distal end portion 106 can be placed within the ostium of the pulmonary vein in a percutaneous transluminal procedure and, even more preferably, in a transseptal procedure, as has been indicated otherwise in the present. Therefore, the distal end portion 106 is preferably flexible and adapted to follow and continue along a guidewire seated within the objective pulmonary vein. In a further construction, the proximal end portion 104 is adapted to be at least 30% stiffer than the distal end portion 106. In accordance with this relationship, the proximal end portion 104 may be suitably adapted to provide transmission of push to the distal end portion 106, while the distal end portion 106 is suitably adapted to continue through the flexure anatomy during in vivo administration of the distal end portion 106 of the device in the region of desired ablation. In addition to the specific device constructions that have just been described, other administration mechanisms for administering the ablation member 128 to the desired ablation region are also contemplated. For example, although the variation of Figure 2A is shown as a "wire-over" catheter construction, other guide wire continuation designs are suitable substitutes, such as, for example, catheter devices that are known as "exchange" variations. fast "or" monorail ", wherein the guidewire is only coaxially housed within a lumen of the catheter in the distal region of the catheter. In another example, a deflectable tip design can also be a suitable substitute for independently selecting a desired pulmonary vein and directing the transducer assembly to the desired location for ablation. In addition to this last variation, the lumen of the guidewire and the guidewire of the variation described in Figure 2A can be replaced with a lumen of "pull wire" and associated fixed pull wire that is adapted to deflect the tip of the catheter by applying tension along the varied transitions of stiffness along the length of the catheter. Still further to this variation of pull wire, the acceptable pull wires may have a diameter within the range of about 0.02032 centimeters to about 0.0508 centimeters and may further include a constriction such as, for example, a narrowed outer diameter of approximately 0.0508 centimeters at approximately 0.02032 centimeters. As indicated above, the distal end portion 106 of the delivery member supports an ablation member 128. The ablation member 128 includes an expandable member 108 and an ablation element 120. The expandable member 108 cooperates with the ablation element 120 to position and anchor the ablation element 120 with respect to a circumferential region of tissue. For example, target tissue regions for performing ablation may include a location where a pulmonary vein extends from the left atrium, including the posterior atrial wall of the left atrium, the pulmonary vein ostium, or the pulmonary vein. . In the illustrated device, the expandable member 108 is an inflatable balloon. The balloon has a diameter in a collapsed state that is approximately equal to the external diameter of the distal end portion 106 of the administration member. The balloon 108 may expand to a diameter that generally coincides with the diameter of the circumferential region of tissue and may be expandable to a plurality of expanded positions, in order to work with the pulmonary vein ostium and / or pulmonary veins of different sizes. However, it is understood that the ablation catheter assembly can also include other types of expandable members such as, for example, baskets, cages and similar expandable structures. The expandable balloon 108 can be constructed from a whole series of known materials, although the balloon is preferably adapted to conform to the contour of a pulmonary vein ostium and / or pulmonary vein luminal wall. For this purpose, the material of the balloon can be of a variety with a high compliance, so that the material lengthens when applying pressure and takes the shape of the lumen or body space when it is completely inflated. Suitable balloon materials include elastomers such as, but not limited to, silicone, latex or low durometer polyurethane (eg, a durometer of about 80 A). In addition or alternatively to the construction of the balloon of a material with high compliance, the balloon can be formed to have a completely predefined inflated shape (i.e., having a preform) to generally coincide with the anatomical shape of the body lumen where it is inflated The balloon. For example, the balloon may have a shape that tapers distally to generally coincide with the shape of a pulmonary vein ostium and / or may include a bulbous proximal end to generally coincide with a transition region of the posterior wall of the atrium adjacent to the ostium of the pulmonary vein. In this way, the desired seating within the irregular geometry of a pulmonary vein or vein ostium can be achieved with both balloon variations of compliance and noncompliance. Despite the alternatives that may be acceptable as just described, the balloon is preferably built to have an expansion of at least 300% at 3 atmospheres of pressure and, more preferably, to have an expansion of at least minus 400% at that pressure. It is intended that the term "expansion" here means the outer diameter of the balloon after pressurization divided by the internal diameter of the balloon before pressurization., wherein the inner diameter of the balloon before pressurization is taken after the balloon has been substantially filled with fluid in a taut configuration. In other words, it is intended that in the present "expansion" is related to the change in diameter that is attributable to the compliance of the material in a tension / strain relationship. In a more detailed construction, which is considered to be suitable for use in most conduction block procedures in the region of the pulmonary veins, the balloon is adapted to expand under a normal pressure scale, so that its outer diameter it can be adjusted from a radially collapsed position of approximately 5 millimeters to a radially expanded position of approximately 2.5 centimeters (or approximately an expansion of 500%). The ablation element 120 cooperates with the expandable member 108, so that the ablation element 120 is held in a generally fixed position with respect to the circumferential region of target tissue. The ablation element may be located outside or within the expandable member or may be located at least partially outside the expandable member. The ablation element, in some forms, also includes a portion of the expandable member. For example, the ablation catheter assembly of Figures 2A and 2B includes an ultrasonic transducer located within the expandable member 108. In a device, the ultrasonic transducer excites a portion of the expandable member 108 during ablation. The specific construction of the ultrasonic transducer and the associated construction of the axis of the administration member holding the transducer are described below. Figure 2B shows details of the distal end portion 106 of the catheter assembly 100 and, in particular, shows the ablation element 120 located circumferentially around an axial center line of administration member 102. A plurality of wires 129 connects the ablation element 120 with a connector 112 at a proximal end of the catheter (shown in Figure 2A). The connector 112 is coupled with a corresponding cable of the ablation control system 118. If the ablation element 120 includes more than one electrode, the lead wire can be connected to all of the electrodes or power sources or separate conductors can be used for allow independent control of each one of the electrodes or energy sources under some operating modes. In Figure 3A a cross-sectional view showing the construction of a typical single cylindrical ultrasonic transducer 300 having a cylindrical internal electrode 302, a cylindrical external electrode 304 and a cylindrical piezoelectric material 303 between the electrodes is shown. The piezoelectric material 303 is a suitable material such as, for example, quartz, PZT and a similar material, which presents a change in the physical dimension in response to a imposed voltage. The piezoelectric material 303 is oriented in such a way that, when a voltage is printed between the electrodes 302 and 304, the thickness of the piezoelectric material 303 changes slightly. When the polarity of the imposed voltage is switched to an ultrasonic frequency F, the piezoelectric material 303 will vibrate at the ultrasonic frequency F. The vibrations of the piezoelectric material 303 produce ultrasonic sound waves. Since the electrodes are cylindrically symmetrical, the piezoelectric material 303 will vibrate radially, with cylindrical symmetry. Conversely, when an ultrasonic wave hits the piezoelectric material 303, the ultrasonic wave will cause vibrations in the piezoelectric material. These vibrations will generate a voltage between the electrodes 302 and 304. Therefore, the transducer is a reciprocal device that can both transmit and receive ultrasonic waves. A detailed construction for a cylindrical ultrasound transducer is shown in Figures 3B and 3C. The length of the transducer 300 or transducer assembly (e.g., disposition of multiple transducer elements) is selected for a specific clinical application. In relation to the formation of circumferential condition blocks in the pulmonary or cardiac vein wall tissue, the length of the transducer may be within the range of about 2032 micrometers to more than 10033 micrometers and, preferably, is equal to about 5080 micrometers to 7493 micrometers. A transducer of this size is considered to form a lesion of sufficient width to ensure the integrity of the conductive block formed without undue tissue ablation.

However, for other applications, the length can be significantly longer. Similarly, the external diameter of the transducer is desirably selected for delivery through a particular access path (eg, percutaneously and transeptally) for proper placement and placement within a particular body space, as well as to achieve a desired ablation effect. In the given application within or proximal to the pulmonary vein ostium, the transducer 300 preferably has an outer diameter within the range of about 1778 microns to more than 2540 microns. It has been observed that a transducer with an external diameter of approximately 2032 microns generates acoustic energy levels approaching 20 watts per centimeter of radiator or more within the myocardial or vascular tissue, which is considered sufficient for ablation of tissue taken by the outer balloon to approximately an outer diameter of the balloon of 3.5 centimeters. For applications in other body spaces, the transducer 300 may have an outer diameter within the range of about 1016 microns to more than 3048 to 4064 microns (e.g., as large as 10160 to 20320 microns for applications in some body spaces). The central glass layer 303 of the transducer 300 has a thickness selected to produce a desired operating frequency. Of course, the frequency of operation will vary depending on the clinical needs, such as in relation to the tolerable external diameter of the ablation and the depth of the heating, as well as depending on the size of the transducer limited by the administration route and the size of the target site . As described in more detail below, transducer 300 in the illustrated application operates, preferably, within the range of about 5 MHz to about 20 MHz and, most preferably, within the range of about 7 MHz to about 10 MHz. MHz. Therefore, for example, the transducer may have a thickness of approximately 304.8 micrometers for an operating frequency of approximately 7 MHz (eg, a thickness generally equal to 1/2 of the wavelength associated with the frequency of desired operation). The transducer 300 is vibrated along the wall thickness and to radiate acoustic energy collimated in the radial direction. For this purpose, the distal ends of the electrical conductors 336, 337 are electrically coupled with the inner and outer tubular members or electrodes 304, 302, respectively, of the transducer 300 as, for example, by welding the conductors to the covers metallic or by means of resistance welding. In the illustrated device, the electrical conductors are made of silver wire from 101.6 to 203.2 micrometers (0.01016 to 0.02032 centimeters) or the like. The proximal ends of these conductors are adapted to be coupled with an ultrasonic driver or driver 340, which is schematically illustrated in Figure 3B.

The transducer 300 may also be divided by engraving or cutting notches in the external transducer electrode 304 and part of the central piezoelectric crystal layer 303 along lines parallel to the longitudinal axis L of the transducer 300, as illustrated in FIG. 3C. The division basically electrically isolates the external transducer electrode 304 creating, in effect, separate transducers. A separate electrical conductor is connected to each of the sectors to couple the sector of a directed energy control that individually excites the corresponding transducer sector. By controlling the drive power and the operating frequency for each individual sector, the ultrasonic controller 340 can improve the uniformity of the acoustic energy beam around the transducer 300, as well as it can vary the degree of heating (i.e., injury control) in the angular dimension. However, in this configuration, the acoustic energy remains highly collimated in the radial direction and does not allow the acoustic beam to project forward or backward. Figures 3D and 3E illustrate the pathways of the collimated radial acoustic energy beam 320 when the ablation device is placed in a pulmonary vein 325 and pulmonary vein ostium 330, respectively. The present invention utilizes a tissue ablation element and device assembly that are capable of creating a circular energy beam that can be phased in the longitudinal direction, orienting the beam forward or backward. In one embodiment of the invention, the ablation element is a thin-wall ultrasonic transducer sectioned into a small number of helical transducer segments interleaved with many turns that form a spiral arrangement. Figures 4A to 4C are perspective, side and end views, respectively, showing the construction of a spiral arrangement of segments of ultrasonic transducers in accordance with one embodiment of the present invention. The arrangement is made from a piezoelectric transducer in the form of a single tube 400 having a longitudinal axis 410. The transducer 400 comprises a piezoelectric crystal 403 between an internal electrode 402 and an external electrode 404. The transducer 400 is approximately 8255 micrometers in diameter. length, with an outer diameter of approximately 2540 micrometers and a wall thickness of approximately 457.2 micrometers. The external electrode 404 is segmented by notches engraved in a small number of interlocking individual helical elements 405 having a plurality of turns. Each individual element 405 is basically electrically isolated from the other elements, allowing the segmented elements to operate independently with minimal interference. In effect, this configuration basically forms an array of functionally discrete transducers with a helical shape arranged linearly along the longitudinal axis 410. Hereinafter, these functionally discrete apparent transducers will be referred to as transducer segments. When operated out of phase, the helical phase disposition configuration allows the transducer 400 to achieve phase coherence equal to many more serially phased individual transducers located axially along the longitudinal axis 410. For the purposes of For example, the illustrated embodiment shows a transducer 400 having an external electrode 404 divided into five (5) elements 405 (405a to 405e) corresponding to five (5) discrete transducer segments 400a to 400e. Each transducer segment 400a to 400e comprises twenty (20) turns, providing phasing coherence of approximately one hundred (100) separate phased transducers arranged serially along the longitudinal axis 410. The number of elements 405, Transducer segments (400th a 400e) and illustrated turns is illustrative. The person skilled in the art would understand that other configurations are contemplated by the present invention, which have less or more helical elements 405. Several factors, including the desired application, can contribute to these other configurations. Each individual helical element 405 has an elongate element pad 406 (406a to 406e) that serves as a connection point for the lead wires (not shown) used to energize the individual transducer segments 400a to 400e respectively. Each of these element pads 406 is basically electrically isolated from one another to limit interference between the individual elements 405. In addition, a ground pad 407 joins the internal electrode 402 and provides a connection point for a wire to Earth.

The illustrated embodiment has six (6) pads (five element pads 406a to 406e and a ground pad 407). Each pad is equally spaced around the circumference of transducer 400, approximately sixty (60) degrees from each other. However, this configuration should not be considered as limiting the scope of the invention. Instead, it is only necessary that each element pad 406 is substantially electrically insulated from one another to minimize interference and crossing between the elements 405, regardless of the configuration. In a preferred embodiment, the junction of the conductor and ground wires is made by welding the wires directly to the element and ground pads 406, 407 respectively. When an electric potential is applied along a particular end pad 406 associated with a given element 405 and the ground pad 407, the segment (400a to 400e) associated with the particular end pad 406 is energized. As previously described, the transducer 400 is divided into a small number of interleaved individual helical transducer segments (400a to 400e) which are basically electrically isolated from one another by means of notches etched through at least the electrode external 404. This transducer design is sensitive to material defects, since any cracking or imperfection could disconnect an entire segment. In addition, any discontinuous notch would shorten two segments. To minimize these potential problems, a suitable raw material for the transducer would include a high density fine grain PZT ceramic material with a porosity of less than 25.4 micrometers. When the transducer is manufactured, the raw PZT ceramic material space is originally in the form of a block or hub and can be transformed into a tubular configuration using known milling methods. In a preferred embodiment, the ceramic material space PZT is drilled in the center and milled using a computer numerically controlled machine (CNC machine) to form a tubular configuration with an inner diameter of approximately 2540 micrometers and an outer diameter of approximately 3048 micrometers, providing a wall thickness of approximately 254 micrometers. The overall length of the PZT ceramic cylinder is also milled at approximately 8255 micrometers. The concentricity should be less than 25.4 micrometers at each end of the tube. This tubular PZT ceramic material forms what will ultimately become the piezoelectric material 303. In a preferred embodiment, a quadruple YAG laser at a wavelength of approximately 700 nanometers, coupled to a rotating CAD / CAM mandrel, is used for milling the space of ceramic material PZT to form the tubular configuration. The outer surface of the PZT 403 cylinder is then polished using methods known in the art. An acceptable method of polishing the PZT 403 cylinder involves mounting the cylinder 403 on a mandrel that rotates and rotates the mandrel at high speed, at which time the cylinder 403 comes into contact with a very fine abrasive material, such as sandpaper or cloth. It has been found that rotational speeds of about 30,000 RPM or more are acceptable. The polished finish creates a smooth and very thin surface that facilitates the subsequent metallic deposition that makes up the electrodes. In addition, the polished surface reduces the possibility of cracking or defects in the metal electrode surface, producing a very uniform and even metallic layer. The uniform metallic layer allows the engraving or subsequent cutting of very fine patterns or notches. In a preferred embodiment, a polished mirror finish of 10 microns or less will allow the laser engraving process to produce notches of 30 to 50 microns. The tubular ceramic material PZT 403 is then covered with one or more metallic layers to form the inner and outer electrodes 402, 404, respectively, as shown in step 815. In a preferred embodiment, the ceramic material PZT 403 is first sprayed with gold to be later nickel plated. The spraying procedure involves placing the ceramic PZT 403 tube in a vacuum chamber and bombarding the tube with gold ions produced using high temperatures and intense static electric fields between a cathode and an anode.

In one embodiment of the invention, the spraying process involves placing the ceramic PZT tube 403 in a vacuum chamber equipped with a cathode and an anode. The cathode typically consists of a metal lens made of the same metal to be deposited (sprayed) into the ceramic PZT 403 tube. All the remaining air in the vacuum chamber is evacuated and the chamber is filled with a low pressure gas, such as argon. A high voltage is applied between the cathode and the anode, ionizing the gas and creating what is known as the dark space of Crookes near the cathode. In the illustrated embodiment, it is desired to spray gold on the PZT 403 tube. Accordingly, the objective is a gold cathode. Almost all the potential high-voltage supply appears throughout the dark space. The electric field accelerates the argon atoms, which bombard the target gold. There is an exchange of speed and an atom is expelled from the target material (in this embodiment, a gold atom) and is deposited in the ceramic PZT tube 403, where it adheres and forms a metallic gold film. The PZT 403 tube is rotated and moved during the procedure to ensure adequate gold coverage in all directions. Once the gold spraying has been completed, the covered PZT 403 pipe is veneered using a plating procedure. In a preferred embodiment, the covered PZT tube 403 is nickel-plated by dipping the tube 403 into a nickel-acid solution. Using a small electric current, the nickel is removed from the solution and deposited on the exposed surfaces of the tube.

When patterns are engraved or cut, such as the spiral notches that make up the helical elements 405, on the surface of the transducer, the transducer becomes extremely brittle. To minimize fatigue and transducer failures during the milling procedure, the transducer assembly 400 is mounted on a mandrel prior to milling the notches, as shown in step 820. The mandrel provides additional structural support until a layer The coincident, described below, is placed on the transducer assembly 400. The metallic covered tube is then milled to form the internal and external electrodes 402, 404, respectively, as shown in step 825. In a preferred embodiment, the process of milling to form the electrodes 402, 404 comprises laser engraving the metal cover. The combination of these materials (402, 403, 404) forms the transducer 400. Both metallic coating processes are well known in the art and can use other metals, other than gold and nickel, in the process. In addition, the spraying process can be eliminated when manufacturing ultrasound transducers. However, the spraying process produces a stronger adhesion of the metal to the ceramic PZT material and, therefore, is the preferred method. The segmentation of the transducer 400 can be achieved by engraving or cutting spiral notches in at least the external electrode 404 of the transducer 400, separating the transducer 400 into discrete operating transducer segments (400a to 400e). The notches can be fabricated using several different methods known in the art such as, for example, etching by means of a laser or diamond grindstone. A particular laser milling method that can be adapted to cut helical grooves is described by Corbett, Scott et al. in "Laser Machining of High Density Two-Dimensional Ultrasound Arrays" (2002), which is incorporated by reference in its entirety herein. This method uses a YAG laser that emits a wavelength of 355 nm to basically record or evaporate the material and create the 405 elements. Other milling methods capable of achieving the desired configuration, such as those used for laser engraving I stents and other medical devices can be used and are known in the art. In a preferred embodiment, an Nd-YAG laser is coupled with an exact CNC system to cut the pattern within a few microns. The helical notches engraved or cut by the laser are approximately 76.2 micrometers deep and 50.8 micrometers wide. The end pads of elements 406 and ground pad 407, as well as the end notches that disconnect the inner electrode 402 from the external electrode 404, are formed in a similar manner using the laser and the CNC machine. When patterns are engraved or cut, such as the spiral notches that make up the helical elements 405, on the surface of the transducer, the transducer becomes extremely brittle. To minimize fatigue and transducer failures during the milling procedure, the transducer assembly 400 is mounted on a mandrel before milling the notches. The mandrel provides additional structural support until a matching layer, described below, is placed over the transducer assembly 400. The helical elements 405 are shortened and the transducer 400 is coiled in the thickness mode. Berlingado is known in the art and refers to the process of orienting the molecules of the ceramic material PZT, basically transforming the ceramic material PZT into a piezoelectric crystal. The berlingado is achieved by heating the PZT ceramic material beyond its Kerrie point and applying a strong electric field. In one embodiment of the present invention, the ceramic material PZT is heated to approximately 500 degrees C, while an electric field of approximately 500 volts direct current (DC) is applied. There is no need to beriing each transducer segment (400a to 400e) separately. Instead, it would be sufficient to shorten all of the five segments and apply a voltage between all of the five transducer elements 405a to 405e and the ground electrode 402 together. A multicoaxial wire is then attached to the transducer 400. In the illustrated embodiment, the multicoaxial wire includes six (6) wires, one from each of the transducer segments (400a to 400e), ie each of the element pads 406 and a ground conductor. In a preferred embodiment, the wires are attached to the element pads 406 and ground pad 407 by welding. A matching layer is then placed on the transducer 400, contributing to the strength and operability of the transducer assembly 400. As described above, the matching layer provides the transducer 400 with the mechanical strength lost during the etching operation. A ceramic PZT tube with fine notches etched into the surface, as provided in a preferred embodiment of the present invention, would fracture and / or fail without an outer cover holding the material in place. The matching layer also increases the bandwidth of each transducer segment (400a to 400e) and, therefore, the overall bandwidth of the transducer 400. As described in more detail below, this feature allows an operation scale of higher frequency for each transducer segment 400a to 400e. Projecting the acoustic energy beam forward or backward with respect to the longitudinal axis of the transducer 400 requires that the transducer segments 400a to 400e be operated out of phase one relative to the other. Any change that you wish to make to the angle of the acoustic energy beam is proportionally related to the frequency. Accordingly, the larger the bandwidth of the transducer segments 400a to 400e, the greater the spectrum (wider angle) in which the transducer 400 can project the acoustic energy beam.

The matching layer also provides electrical insulation between the transducer elements 405. In a layout design, the matching layer is formed from a polymer laminated on the transducer elements 405, leaving the notches separating the transducer elements 405 filled with air. This configuration allows the acoustic separation between the transducer segments 400a to 400e and ensures a uniform thickness of the matched layer. However, when the transducer 400 is used for high intensity ultrasound applications, the applied voltage between the adjacent transducer segments 400a to 400e may be relatively high. This high voltage coupled with the relatively large distance that adjacent transducer elements 405 travel in parallel increases the risk of current leakage between adjacent transducer segments 400a through 400e. However, the air-filled notches provide little or no resistance to this leakage. Accordingly, in another more preferred embodiment, the transducer 400 is coated with a matching layer, preferably a low viscosity polymer, which is introduced and filled with the notches separating the transducer elements 405. The matching layer must also cover the transducer 400 with a thin polymer layer, with a thickness of approximately 50.8 micrometers. The polymers used in the matching layer must have a low viscosity, good adhesion to the metal and ceramic material, low coefficient of expansion, as well as a reasonably high dielectric strength. An example of a polymer having such characteristics is an epoxy adhesive.

In addition to the rolling process, the matching layer can be coated on the transducer 400 by other methods known in the art, including spray coating with an air or airless spray, dip coating, chemical vapor deposition, coating with plasma, coextrusion coating, spin coating and molding with inserts. Figures 5A and 5B are close sectional views, respectively, showing the construction of a transducer 500 segmented by interlaced individual helical elements 505 (505a to 505e) basically in a disposition of functionally discrete transducer segments 500a to 500e in accordance with a embodiment of the present invention. The transducer 500 has an internal electrode 502 as a common electrode, as well as a cylindrical piezoelectric material 503 as a common element. The outer electrode 504 is segmented by the spiral notches 510 to form 5 individual helical electrodes 505 (505a to 505e) helically disposed about the surface of the external transducer 500. The helical electrodes 505a through 505e are basically electrically isolated from each other and correspond to the arrangement of five segments of helical transducers 500a to 500e. When an alternating current (AC) voltage is applied between the inner electrode 502 and a selected one of the five outer electrode elements 504 (505a to 505e), the piezoelectric material vibrates in the region between the inner electrode 502 and the second external electrode element 505. For example, an applied AC voltage between the inner electrode 502 and the external electrode element 505a will cause the region between the electrode 502 and the electrode element 505a to vibrate. However, the piezoelectric material 503 is a single piece of an unseparated material, as shown in Figures 5A and 5B, so that the applied voltage and the subsequent vibration between the inner electrode 502 and the outer electrode element 505a will cause something of vibration in the regions between the inner electrode 502 and the outer electrode elements 505b and 505e adjacent the electrode element 505a. This signal coupling is sometimes called a crossover. Excessive crossing between electrodes may be undesirable for some particular applications. To reduce this coupling between adjacent electrodes, the elements can be partially isolated from each other. Figures 6A and 6B are sectional and sectional close views, respectively, showing the construction of a transducer 600 having extended notches in the cylindrical piezoelectric material 603 in accordance with one embodiment of the present invention. By extending the notches in the piezoelectric material 603, the piezoelectric material 603 will be zoned, partially isolating the signals and subsequently reducing the crossing. As described above in a similar manner, the transducer 600 is constructed with interlocking individual helical elements 605 that section the transducer 600 into an array of functionally discrete transducer segments with spiral shape 600a 600e. The transducer 600 has an internal electrode 602 as a common electrode and a cylindrical piezoelectric material 603 at least partially as a common element. The external electrode 604 is separated by spiral notches 610 into 5 individual helical electrode elements 605 (605a to 605e) helically disposed about the surface of the external transducer 600. These helical elements 605a through 605e correspond directly to the transducer segments 600a a 600e. However, unlike the transducer 500 illustrated in Figures 5A and 5B, these spiral notches 610 extend radially completely through the external electrode and into at least a portion of the cylindrical piezoelectric material 603. The notches in the piezoelectric material 603 they will tend to physically separate the piezoelectric material 603 into zones (five zones in the illustrated embodiment) that directly correspond to the five helical electrode elements 605a to 605e. The coupling between the electrodes can be further reduced by extending the spiked notches along the entire length of the piezoelectric material (not shown), thereby producing separate pieces of piezoelectric material and, therefore, completely separate transducers. The transducers 500, 600 can be operated in at least two modes. In a first mode, the totality of the five transducer segments (simulating five helical transducers) is controlled with identical signals. This mode will create a unique radial acoustic energy beam with a radial thickness similar to the unique transducer designs. In a second mode, the five individual segments are controlled as a standard arrangement phased by signals having a fixed phase delay between the segments. Since the segments are arranged to simulate five helical transducers, the phased arrangement allows the resulting energy beam to be directed forward or backward. A delay set in phase is a representation of the time delay in seconds experienced by each sinusoidal component of the input signal. The phase of a periodic phenomenon, that is to say the sinusoidal input signal, can also be specified or expressed with an angular measure, with a period generally encompassing 360 ° (2p radians). When each of the transducer elements is controlled at the same frequency, the phase delay will be directly related to the phase change or the change of phase angle between each sinusoidal component of the input signal. A schematic representation illustrating a fixed phase delay (phase change) for a plurality of sinusoidal input signals 720 (720a to 720e) controlling an arrangement of transducer segments 700a to 700e is shown in Figure 7A. This design uses a 700 transducer segmented into 5 interleaved helical transducer segments 700a to 700e by five helical elements 705a through 705e. The transducer segments 700a to 700e are controlled through a five-channel generator with five conductors. An advantage of the illustrated configuration is that it can generate a coherent phase-coherent energy beam that simulates more than fifty individual elements. In the illustrated scheme, the like reference numbers are used to show the association between the particular fixed phase input signals 720a to 720e, the transducer elements 705a to 705e and the transducer signals 700a to 700e. For example, transducer element 705a produces a sinusoidal ultrasonic sound wave 720a. When an alternating sinusoidal input current 720a to 720e is applied between a particular element 705 of the external electrode 704 and the internal electrode 702, the thickness of the piezoelectric material 703 associated with the given transducer segment 700 (700a to 700e) will vibrate at the frequency alternate The repetitive cyclic design illustrated in Figure 7A produces an arrangement that has the same signal every fifth element. Accordingly, the total cumulative phase change along the five transducer segments 700a to 700e is equal to 360 complete degrees. Using a fixed phase delay, the optimum phase change between adjacent transducer segments (700a to 700e) is, therefore, 72 degrees. As can be seen from the illustrated mode, the input signal 720a is 72 degrees out of phase of the input signal 720b. Similarly, the input signal 720b is 72 degrees out of phase of the input signal 720c and so on. This configuration maximizes transducer efficiency and provides a coherent energy beam. Typically, a cylindrical ultrasound transducer will produce a highly collimated acoustic energy beam emanating from the transducer in a basically normal direction with respect to the longitudinal axis of the transducer. Similarly, a transducer having a plurality of helical segments serially arranged along a longitudinal axis would produce a beam of acoustic energy highly collimated normal with respect to the longitudinal axis of the transducer when the individual transducer segments are phased in. one with respect to the other. However, when the helical segments are controlled out of phase one of another, as illustrated in FIG. 7A, the resulting cumulative acoustic energy beam emanates from the transducer 700 at an angle relative to the longitudinal axis. By varying the phase delay of the input signal 720, the angle of the acoustic energy beam will change. The implication is that, for a different acoustic energy beam angle, a different phase delay would be used. One method for varying the phase delay is to vary the frequency at which the transducer segments are controlled, while maintaining the same phase change (angle) between adjacent input signals. Figure 7B is a schematic representation illustrating the resulting cumulative acoustic energy beams (750, 751, 752) emanating from each of the plurality of transducer element 705a when controlled at different frequencies. The relationship between the acoustic energy beam angle and the operating frequency can be defined using the following formulas: A = V / f and A = L * eos (a) Where: • A is the wavelength of the input signal; • See the speed of sound in the water (1550 m / sec); • f is the frequency at which the transducer elements are controlled; • L is the increase in formation or inclination, which is defined as the linear distance traversed by the helical groove that separates the transducer into helical transducer segments when making a complete turn; • a is the angle between the acoustic energy beam and the longitudinal axis of the transducer. In a preferred embodiment, the increase in L formation is 0.000508 m. By way of example, suppose that it is desired to project the acoustic energy beam at an angle of 45 ° (degrees) from the longitudinal axis (described as beam 751 in Figure 7B). Solving the above equations simultaneously, the arrangement of the transducers 705 would have to be controlled at a frequency of 4.3 MHz. In another example, suppose you want to project the acoustic energy beam at an angle of 60 ° from the longitudinal axis (described as beam 750 in Figure 7B). By once again solving the equations simultaneously, the arrangement of the transducers 705 would have to be controlled at a frequency of 6.2 MHz. Similarly, operating the transducer elements 705 could project an acoustic energy beam 752 at an angle of 30 ° of the longitudinal axis. Figure 7C is a side view of an ablation catheter showing the pathways of acoustic energy beam 751 projected at an angle with respect to the longitudinal axis of the transducer when the ablation device is placed at the junction between a body lumen and a cavity body, such as a pulmonary vein ostium 330. As noted above, an acoustic energy beam can be projected at an angle of 90 ° (ie, perpendicular) with respect to the longitudinal axis at any frequency in the transducer bandwidth , by operating all the segments (700a to 700e) comprising the transducer 700 in phase with each other. In addition, the illustrated arrangement of transducer segments (700a to 700e) can also be controlled with phase delays that are not fixed or would not add 360 ° as described above. Several factors must be considered when choosing a generator to produce the acoustic energy beam. The generator must have at least one channel for each electrode element (ie, for each transducer segment). Using the illustrated mode as an example, the generator would be, at a minimum, a five-channel signal generator with an amplifier output stage capable of phase-locked operation. A linear RF amplifier must be provided for each matching channel to operate a load of 50 Ohms up to 20 watts per channel. The amplifiers must have a bandwidth of up to 12 MHz and must have an identical phase and gain change along the channels. Preferably, the generator must have directional couplers, bypass resistors to dissipate the reflected energy and phase detection and magnitude of reflected energy circuits. Preferably, the signal generator would be a computer controlled signal generator capable of generating highly coherent continuous sine wave signals with exact phase delay between the channels. The computer must be able to obtain the desired angle as an input and calculate the frequency and phase for each of the five channels. Other desirable inputs to the computer should include the desirable output energy, the direct and reflected energy of each channel, and the temperature of the target tissue. If the transducer is also to be used for imaging, appropriate considerations should be made regarding the design of the generator, such as the ability to generate short bursts of acoustic energy with exact timing. The preceding invention shows various assembling forms of circumferential ablation devices incorporating ultrasound transducers for ablating a circumferential region of tissue. Such ultrasonic ablation assemblies are considered particularly suitable for use with position monitoring assemblies that incorporate transducer sensing capabilities such as, for example, but without limitation, an "A" mode detection system. However, it is further contemplated that the particular ablation devices may also be combined with other position monitoring assemblies and related sensors. Additionally, such ultrasound ablation assemblies can also be combined with the different ablation monitoring assemblies, such as sensors and temperature monitoring assemblies. As common as each of the following devices, a source of acoustic energy is provided with a delivery device that may also include an anchoring mechanism. In one mode, the anchoring device comprises an expandable member that also positions the source of acoustic energy within the body. However, other anchoring and positioning devices can also be used, such as, for example, a basket mechanism. In a more specific form, the source of acoustic energy is located within the expandable member and the expandable member is adapted to take a circumferential pathway of tissue either around or along a pulmonary vein in the region of the ostium, throughout of a left atrial wall. The acoustic energy sources of the prior art are acoustically coupled, however, with the wall of the expandable member and, therefore, with the circumferential region of tissue taken by the wall of the expandable member by emitting a longitudinally and circumferentially collimated ultrasound signal. when they are operated by means of an acoustic energy controller. The use of acoustic energy, and particularly of ultrasonic energy, offers the advantage of simultaneously applying a dose of sufficient energy to ablate a relatively large surface area within or near the heart at a desired heating depth without exposing the heart to a large amount of current. For example, an ultrasonic transducer can form a lesion, which is approximately 1.5 mm wide, with a lumen approximately 2.5 mm in diameter, such as a pulmonary vein, and with sufficient depth to form an effective conductive block. It is thought that an effective conductive block can be formed by producing a lesion within the tissue that is transmural or basically transmural. Depending on the patient, as well as the location within the ostium of the pulmonary vein, the lesion may have a depth of 1 millimeter to 10 millimeters. It has been observed that the ultrasonic transducer can be energized to provide a lesion having these parameters, so that it forms an effective conductive block between the pulmonary vein and the posterior wall of the left atrium. Although the particular detailed description has been provided herein for specific embodiments and variations in accordance with the present invention, it is further understood that various modifications and improvements may be made by the person skilled in the art in accordance with this description and without deviating from the broad scope of the invention.

In addition, a circumferential ablation device assembly constructed with an ultrasound ablation element mounted in accordance with the present invention may be used in conjunction with other linear ablation methods and assemblies, as well as various components or related steps of said assemblies or methods, respectively, in order to form a circumferential conduction block for the formation of long linear lesions, as in a less invasive "labyrinth" type procedure. In addition, the person skilled in the art can make other modifications or improvements obvious or not substantial to the specific embodiments shown and described herein, based on this description, without deviating from the scope of the invention as defined by the following claims.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A cylindrical ultrasound transducer comprising: a cylindrical internal electrode; a cylindrical piezoelectric material disposed on the internal electrode; and a cylindrical external electrode disposed on the cylindrical piezoelectric material, the cylindrical external electrode having spiral notches separating the external electrode into a plurality of discrete helical elements.

2. The cylindrical ultrasound transducer according to claim 1, further characterized in that the internal electrode comprises a metal layer.

3. The cylindrical ultrasound transducer according to claim 2, further characterized in that the metallic layer comprises nickel.

4 - The cylindrical ultrasound transducer according to claim 2, further characterized in that the metallic layer comprises gold.

5. The cylindrical ultrasound transducer according to claim 1, further characterized in that the cylindrical piezoelectric material comprises a high density fine grain ceramic PZT material.

6. - The cylindrical ultrasound transducer according to claim 1, further characterized in that the cylindrical piezoelectric material is polished with a mirror finish of approximately 10 microns.

7. The cylindrical ultrasound transducer according to claim 1, further characterized in that the external electrode comprises a metal layer.

8. The cylindrical ultrasound transducer according to claim 7, further characterized in that the metallic layer comprises nickel.

9. The cylindrical ultrasound transducer according to claim 7, further characterized in that the metallic layer comprises gold.

10. The cylindrical ultrasound transducer according to claim 1, further characterized in that the discrete helical elements are interlinked with each other.

11. The cylindrical ultrasound transducer according to claim 1, further characterized in that the spiral notches further separate the piezoelectric material in a plurality of substantially discrete zones.

12. The cylindrical ultrasound transducer according to claim 11, further characterized in that the zones are helical in shape and interlocked with each other.

13. - The cylindrical ultrasound transducer according to claim 1, further characterized in that it comprises a matching layer disposed on the external electrode.

14. The cylindrical ultrasound transducer according to claim 13, further characterized in that the matching layer fills the notches.

15. The cylindrical ultrasound transducer according to claim 13, further characterized in that the matching layer comprises a polymer of low viscosity.

16. The cylindrical ultrasound transducer according to claim 13, further characterized in that the polymer is an epoxy adhesive.

17. A cylindrical ultrasound transducer comprising: a cylindrical internal electrode; a cylindrical piezoelectric material disposed on the internal electrode; an external cylindrical electrode disposed on the cylindrical piezoelectric material; and spiral notches cut through the outer electrode and at least a portion of the cylindrical piezoelectric material, the spiral notches separating the transducer into a plurality of functionally discrete helical transducer segments.

18. An ablation element comprising a plurality of intertwined helical transducers arranged linearly along a longitudinal axis.

19. - An ablation element comprising an ultrasonic transducer segmented into a plurality of functionally discrete intertwined helical transducer segments arranged linearly along a longitudinal axis.

20. An ablation catheter assembly for ablating a tissue region in a body space, comprising: an elongate delivery member having a proximal end portion and a distal end portion; an anchor mechanism coupled with the distal end portion of the elongated delivery member, the anchor mechanism being adapted to take a substantial portion of tissue in the body space; and an ablation element attached to the distal end portion of the elongate delivery member, the ablation element having an ultrasonic transducer segmented into a plurality of functionally discrete interleaved helical transducer segments disposed linearly along a longitudinal axis.