Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M25/00—Catheters; Hollow probes
  • A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
  • A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
  • A61M25/0133—Tip steering devices
  • A61M25/0147—Tip steering devices with movable mechanical means, e.g. pull wires
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
  • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
  • A61B18/14—Probes or electrodes therefor
  • A61B18/1492—Probes or electrodes therefor having a flexible, catheter-like structure, e.g. for heart ablation
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
  • A61B17/00234—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery
  • A61B2017/00238—Type of minimally invasive operation
  • A61B2017/00243—Type of minimally invasive operation cardiac
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
  • A61B17/00234—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery
  • A61B2017/00292—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery mounted on or guided by flexible, e.g. catheter-like, means
  • A61B2017/003—Steerable
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B2018/0091—Handpieces of the surgical instrument or device
  • A61B2018/00916—Handpieces of the surgical instrument or device with means for switching or controlling the main function of the instrument or device
  • A61B2018/0094—Types of switches or controllers
  • A61B2018/00952—Types of switches or controllers rotatable
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
  • A61B90/36—Image-producing devices or illumination devices not otherwise provided for
  • A61B90/37—Surgical systems with images on a monitor during operation
  • A61B2090/374—NMR or MRI
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M25/00—Catheters; Hollow probes
  • A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
  • A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
  • A61M25/0133—Tip steering devices
  • A61M2025/0161—Tip steering devices wherein the distal tips have two or more deflection regions

Definitions

• the distal assembly 34 comprises a core 40 which has a proximal portion 41 adapted to be received in the distal tip 34 of the tipstock 32, and a compressible head 42 at its distal end.
• the compressible head 42 includes anchor tabs 47a, 47b.
• the core 40 has a longitudinal slot 44 extending proximally from its distal face which permits the anchor tabs 47a, 47b to resiliently flex toward each other as the core 40 is received within an aperture 45 in a hollow non-magnetic (e.g. gold) ablation electrode 46 ( Figure 15a).
• the core 40 is preferably made of a nonmagnetic material having a low temperature coefficient, such as the ULTEM ® polyetheraide 1000 resin produced by the GE Plastics division of the General Electric Company, Pittsfield, MA.
• the low temperature coefficient material provides thermal insulation between the ablation electrode 46 and the tipstock 32, and, preferably, the core 40 has a lower thermal mass than the ablation electrode.
• the provision of the core 40 between the tipstock 32 and the ablation electrode 46 reduces the likelihood of catheter damage during an ablation procedure which better ensures that a single catheter can be used for a given procedure, or perhaps reused (once sterilized) in subsequent procedures.
• the cap electrode 46 and the distal tip 34 of the tipstock 32 may be spaced from each other once the core 40 has been mounted in the distal tip 34 by a thin bead of epoxy, or by an annular ring on the core 40, disposed between its proximal end 41 and the compressible head 42. Further, a wider range of materials can be selected for the tipstock 32, including materials with melt-temperatures that are significantly less than the expected ablation temperature, such as polyurethane. With further reference to Figures 14 and 15 A, the distal assembly 34 preferably serves as an anchor for the steering wire 38 and also preferably houses a temperature sensor 54.
• the tipstock 32 is connected to the distal end of the shaft 30 in conventional manner, preferably along complementary tapered and overlapping regions at their distal and proximal ends, respectively, by ultrasonic welding (Figure 15B).
• the assembly of the distal tip assembly 24 is as follows.
• the plastic core 40 is preferably injection molded.
• the ablation electrode 46 is machined to have the desired overall dimension for the size of catheter with which it is to be used.
• the machining is preferably performed under computer control using a machine that can select a first drill bit to generally hollow out the ablation electrode 46, then a second, smaller bit to define the cavity 96, and finally to form the groove 48 using a key cutter, for example, by circular interpolation as understood by those of ordinary skill in the art of machining.
• Conductive wire 52 is preferably wrapped like a lasso and resistance welded to the ablation electrode 46.
• a teflon coated steering wire 38 is selected, the portions of the steering wire 38 that are anchored to the core 40 and the control handle 24 preferably being stripped clear of the teflon. Teflon is difficult to bond and is removed to anchor the exposed steering cable.
• a lubricous sleeve such as teflon may be bonded to the steering wire 38 to reduce the frictional forces that are imparted by the walls of lumens 70, 78 when the steering wire is moved and electrically insulate the steering wire.
• a second steering wire 38A may be threaded through lumens 98 disposed on the opposite side of the central lumen 94.
• the ablation electrode 46 may be filled with a potting compound 102 such as FDA-2 epoxy and the core and ablation electrode snapped together in the manner previously described.
• a potting compound 102 such as FDA-2 epoxy and the core and ablation electrode snapped together in the manner previously described.
• the snap action of the core 40 and ablation electrode 46 is both audible and tactile.
• the steering wire, thermistor wires, and ablation electrode wire are received without any twisting action unlike other known methods of making an ablation catheter.
• the potting compound 102 electrically and thermally isolates the steering wire 38 from the ablation electrode 46.
• Radiofrequency ablation was performed using a standard clinical RF generator (Atakr®, Medtronic, Minneapolis, MN) with open loop control.
• the generator was located outside the scan room and was electrically interfaced to the animal via the above described ablation catheters.
• the dispersive ground electrode consists of a large conductive adhesive pad that is attached to the skin of the animal to complete the circuit.
• Intracardiac electrogram tracings were acquired using the same catheters via a similar 12-channel shielded filter box and were recorded using automated data acquisition software. The effect of the RF ablation signal on image quality is shown in Figure 1.
• the left panel represents an image acquired during RF delivery without filtering while the image on the right shows the same slice during RF delivery with filtering. Note that there is no evidence of noise or artifact and the tip of the catheter is clearly visible in the right ventricular apex (arrow).
• a 7F non-magnetic single electrode ablation catheter was positioned at the inferior lateral wall of the right atrium in three animals to determine the accuracy of catheter localization under MR guidance (no ablation).
• FGRE fast gradient recall echo
• the catheter was imaged to isolate the optimal tomographic slice containing the catheter electrode. After baseline images were acquired for this slice prescription, RF ablation was performed in the right ventricle between the distal electrodes and a large surface area skin patch at a power of 20 W for 60 seconds. To avoid electrode coagulum formation, impedance was monitored by an automatic open-loop feedback system that terminates RF delivery if the impedance exceeds 220 ohms.
• FSE fast spin echo
• the animal was sacrificed by anesthesia overdose and the heart was excised and sectioned through the right ventricular lesion into slices corresponding to the tomographic MR imaging slices. Lesion location, morphology, width, length and transmural extent were determined and recorded at gross examination and right ventricular lesions were photographed and matched with the corresponding T2 and contrast enhanced Tl -weighted lesion images. Sections from thermally damaged tissues were bisected longitudinally and submitted for histologic staining (Masson's trichrome and hematoxylin-eosin).
• Specimens were then analyzed under light microscopy at 40X to characterize global morphologic changes (9) (e.g., delineated cellular junctions and nuclei, and interstitial edema) for determination of the degree of heat induced cellular damage and necrosis.
• global morphologic changes 9 (e.g., delineated cellular junctions and nuclei, and interstitial edema) for determination of the degree of heat induced cellular damage and necrosis.
• lesion signal intensity, length, width and area were measured directly from MR images using an off-line quantitative analysis package (Image Tool, Scion Image, Bethesda, MD). Each parameter was measured 10 times for each time frame from baseline to 20 minutes post-ablation. Mean signal intensity from region of interest (ROI) measurements was then normalized (mean ROI signal intensity at time t divided by the baseline signal intensity) and plotted as a function of time. A similar method was used following gadolinium injection on Tl -weighted imaging. Additionally, IEGMs were analyzed pre and post-ablation for changes in signal amplitude and waveform shape.
• ROI region of interest
• a MR fluoroscopy sequence was used to successfully position the non- steerable catheter at atrial and ventricular target sites in all animals.
• MR catheter placement was attempted to target the inferior lateral wall of the right atrium from a jugular access ( Figure 2). Images were acquired without breath-hold once every heart beat with one-second updates. Details of the right atrial anatomy could be appreciated in all animals as several major endocardia! anatomic landmarks were successfully identified, including the superior and inferior vena cava, atrial septum, right atrial appendage, coronary sinus, eustachian ridge, fossa ovalis and tricuspid valve. The catheter remained in the imaging plane throughout the entire navigation sequence in 2 of 3 animals.
• T I - FGRE images of the same tomographic slice were acquired before and following 7 ml peripheral gadolinium injection ( Figure 5a,b).
• the lesion border was clearly demarcated 60 seconds following contrast injection.
• a lesion profile is simply a plot of signal intensity over a fixed spatial domain passing though the lesion, as illustrated by Figure 7a for a single time frame.
• the three- dimensional surface plot represents a series of these profiles in time, where the z-axis represents the color-coded signal intensity and the x and y-axes represent position and time following RF delivery, respectively.
• the lesion grew dramatically in signal intensity and size from the baseline level shown by the arrow. Maximum signal intensity and lesion area were achieved 12.2 ⁇ 2.1 and 5.3 ⁇ 1.4 minutes following RF delivery, respectively.
• This study concerns a novel MRI-compatible interventional electrophysiology hardware system in conjunction with a newly developed real-time interactive cardiac MRI system to characterize the temporal and spatial development of cardiac lesions following radiofrequency ablation.
• This finding indicate that: 1) MR images and IEGMs can be acquired during radiofrequency ablation therapy using specialized radiofrequency filters; 2) nonmagnetic MR compatible catheters can be successfully placed at right atrial and right ventricular targets using fast MR imaging sequences with interactive scan plane modification; 3) regional changes in ablated cardiac tissue are detectable and can be visualized using FSE and FGRE images; 4) the spatial extent of heat induced necrosis can be accurately quantified by MRI immediately following thermal damage; and 5) lesion transmurality can be assessed. These results may have significant implications for the guidance, delivery, and monitoring of cardiac ablation therapy by interventional MRI.
• MR guided catheter placement Another very important feature of MR guided catheter placement is the ability to visualize the electrode-endocardial tissue interface, which has been shown to increase lesion size by improving the efficiency of RF tissue delivery. While traditional indicators of electrode contact such as fluoroscopic catheter stability and intracardiac electrogram amplitude are useful, these parameters are relatively insensitive indicators of electrode-tissue contact.
• An important limitation of passive MR catheter tracking is the need to manipulate the catheter within the imaging slice (typically 5- 10 mm wide), which may be especially difficult during catheter placement in geometrically complex vessels and cardiac chambers where catheter curvature and loops are common.
• FGRE imaging is preferable to FSE for cardiac ablation therapy since imaging times are decreased significantly and quality images may be acquired without cardiac gating and breath-holds.
• An important parameter for contrast-enhanced lesion imaging is the duration post-ablation for optimal gadolinium uptake, hi this study we injected contrast 30 minutes post-ablation and observed a rapid uptake of gadolinium in the affected area of the myocardium. It is not known, however, how quickly the lesion is capable of contrast uptake. The answer to this question has direct clinical implications and may also lend additional insight into the biophysical mechanisms of in vivo lesion formation.
• MRI guided ablation is not subject to the aforementioned limitations, the technique and system are in the early stages of development and there are number of technical requirements including non-magnetic catheters, monitoring equipment and electromagnetic filtering systems. Additionally, while new advances in scanner hardware have allowed for realtime MR imaging (20 frames/second), passive catheter tracking can be confounded by complex catheter movements that cause the catheter to leave the imaging plane. Lastly, the delayed nature of lesion formation following the initial RTF delivery confounds instantaneous assessment of lesion size.
• the ability to directly visualize the spatial extent of atnial lesions with high spatial resolution may help facilitate the placement of linear transmural atrial lesions and allow for realtime interactive detection and elimination of skip lesions. This potential may have particular importance since it has been shown that ablation lines with skip lesions are not only ineffective but may be arrhythmogenic.
• the ability to characterize the temporal evolution of lesions can be used for therapy titration and avoidance of damage to tissue outside the ablation target volume, although the observed delayed biophysical response of the lesion may confound an instantaneous assessment of lesion size.
• radiofrequency cardiac ablation can be performed under MRI guidance in vivo.
• Catheters are clearly defined and easily positioned in gradient echo images and the spatial and temporal extent of ventricular ablation lesions can be accurately visualized using T2-weighted fast spin echo imaging and Tl - weighted contrast-enhanced fast gradient echo imaging with a standard cardiac phased array thoracic coil.
• lesion size by MRI agrees well with actual postmortem lesion size and high fidelity intracardiac electrophysiologic signals can be acquired and monitored during imaging.
• MRI guided cardiac ablation may be a useful technique that will eliminate ionizing radiation exposure, help provide accurate therapy titration and facilitate the creation of linear, contiguous and transmural lesions, and may lend insight into the physiologic effects of novel ablation techniques and technologies.

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