JP3300954B2 - High impedance, low polarization, low threshold small steroid-eluting pacing lead electrode - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to long-term subcutaneously implanted medical electrode leads, and more particularly, the present invention relates to reducing long-term pacing thresholds and pacing pulse generator power sources. A cardiac pacing lead having a minimized electrode configuration.

2. Description of the Prior Art The safety, efficacy and longevity of a subcutaneously implanted pacemaker device depend to some extent on the performance of the pacing lead, the electronics of the pacemaker pulse generator, the integrity of the pulse generator and the capacity and reliability of the pulse generator power source. Depends on the degree. These interconnected components of the pacemaker device are optimally adapted to the ever-increasing demands on the mode of operation and system operation associated with an overall reduction in size, an increase in service life and the possibility of increasing the reliability of the overall system. Is matched to During the past three decades, the technology of cardiac pacing has made significant progress with subcutaneously implantable pacemakers that exert ever-increasing changes in pacing physiotherapy,
In effect, the range of use of pacemakers has been expanded. With this advance, extensive research and development efforts have been made to optimize the performance of pacing leads and their reliability.

Over the past decade, a reliable and stable long-term pacemaker stimulating effect and a considerable improvement in the sensing threshold have been achieved,
This has led to further miniaturization and longer life of pacemakers, which allows the use of leads with excellent safety margins and reliability. However, as new circuits are created with lower total current consumption, and pacemaker capabilities are constantly increasing in programming capabilities, modes and memory, and as circuits become more complex, the life of the device will become increasingly more characteristic of leads. Became dependent. In addition, those who are implanted subcutaneously will find the pacing lead body thinner so that it occupies less space in the venous system without reducing or reducing the mechanical strength and integrity of the lead body. I got stuck.

In the early days of cardiac pacing, very high geometric surface area electrodes were employed with large, short-lived pacemaker pulse generators. Victor Pars
Early researchers, such as Dr. onnet, were shown in U.S. Pat.No. 3,476,116 to achieve a low polarization and low threshold pacing electrode while exhibiting a relatively small effective surface area for the delivery of stimulating impulses. An advanced type of design known as Differential Flow Density (DCD).

Subsequent researchers, such as Dr. Werner Irnich, have electrodes in considerable detail? The tissue interface was examined and sought to reach the optimal exposed electrode surface area for stimulation threshold and sensing. Dr. Irnich has published a bulletin “Heart pacing” at the 4th International Symposium on Cardiac Pacing, entitled “Considerations for Designing Electrodes for Permanent Pacing,” edited by HJTh
alen: 1973, pages 268-274)
The field intensity (E) required for stimulation is E = v / r (1 / r + d)
Claimed to be variable like 2. v is the applied voltage (threshold:
Volts), r is the electrode radius, and d is the thickness of the fibrous capsule. He further asserts that the average value of d is approximately 0.7 mm, regardless of the electrode radius. for that reason,
Assuming that E is a constant, reducing the electrode radius until r equals d lowers the threshold. When r <d, the threshold starts to increase again. In order to create an exposed surface area of 3 to 6 mm ^2, the exposed hemispherical electrode at the lead end should have a radius of 0.7 to 1.0 mm.
Dr. concludes. However, Dr. Irnich details that he proposes a somewhat different design that employs wire hooks to penetrate the myocardium to hold the electrodes in place. These active fixed wire hook electrodes never became common. And in endocardial pacing leads, passively fixed tines and active screws were replaced.

A paper by FWLindemans and ANEZimmerman entitled "Acute voltage, charge and energy thresholds as a function of electrode size for electrical stimulation of the canine heart" (Cardio
vascular Research Volume XIII, Volume 7
No. 383-391, July 1979), the authors demonstrate that an electrode radius of approximately 0.5 mm is optimal for acute situations. However, as Irnich states, fibrous capsules
It was recognized that when thicker than 0.5 mm, the effect of the small electrode surface area was lost. And for that reason and as stated in various other articles, such small surface area electrodes are unlikely to be used in the long term.

Dr. Seymour Furman also studied the relationship between electrode size and efficiency of cardiac stimulus, and published the Journal of Surgical
In the article entitled "Increasing Electrode Size and Efficiency Decreasing Cardiac Stimulation" in Research, Journal of Surgical Emphysema, Vol. The tip exposed and spaced coil electrode and the small ball electrode are described. The fact that the impedance is increased as an inverse function of the surface area, Furman Dr. the practical lower limit of electrode surface area present per 8 mm ² is concluded.

Cylindrical, ball tip, spiral, circular tip opening the cage, the many forms of electrodes have an exposed electrode surface area of about 8 mm ² including birdcage was pursued in the mid-1970s.

Recently, researchers have emphasized consideration of materials and their relevance for optimizing electrode design.
For example, Medtronic U.S. Pat.
Disclosed early designs of mid-'90s low polarization, low threshold electrodes that included Target Tip ™ Pacing Lead Model 401
It was commercialized as 1, 4012, 4511, 4512, etc. The tip electrode of the lead has a hemispherical and annular groove. The electrodes were made of platinum and the outer surface was plated with platinum black. . The combination of a relatively small electrode surface area and platinum black has become the latest threshold at that time. Other manufacturers have also included porous platinum mesh electrodes (Cardiac Pacemakers), sintered porous electrodes (Cordis), vitreous and vitreous carbon electrodes (Siem) at the same time.
ens) and laser drilled metal electrodes (Telectronics Pp.)
ty) on the market.

A considerable breakthrough in the development of low threshold electrode technology has been described by Stokes in U.S. Pat.
No. 506,680 and related Medtronic U.S. Pat.
This was demonstrated by the steroid-eluting porous pacing electrodes shown in 7,642 and 4,606,118 and 4,711,281. The electrodes disclosed in the '680 patent, although also described for carbon and ceramic compounds, are made from porous sintered platinum or titanium. The electrode has a silicone rubber plug in the ventricle impregnated with an aqueous solution of dexamethasone phosphate or other glucocorticosteroid. Silicone rubber plugs allow steroid release through interatomic gaps in porous sintered metal electrodes,
The electrode tissue interface is reached to prevent or reduce inflammation, irritability and subsequent excessive fibrosis of the tissue adjacent to the electrode. Porous steroid-eluting electrodes
It exhibited substantially lower source impedance as compared to similarly sized solid electrodes. It exhibited significantly smaller peaks and longer pacing thresholds compared to solid or porous electrodes of the same size. The two advantages of steroid eluting electrodes are that they allow the use of relatively small surface area electrodes of about 5.5 mm ² to increase pacing impedance without sacrificing the ability to sense cardiac activity. Yes (CAPSVRESP model 502
3, 5523 Lead (trademark): manufactured by Medtronic). If more efficient stimulation of heart tissue due to lower current consumption can be achieved from a subcutaneously implanted pacemaker power source, higher currents during stimulation pulses with smaller electrode sizes according to the '680 patent invention. Generate density. In addition, the localized nature of drug treatment minimizes systemic anabolic effects of the drug and avoids side effects that are undesirable for the patient.

Medtronic, Inc. CAPSVRE model of the surface area 8mm ² of 4003,450
Elution leads for 3,4004, 4504 steroids are currently very popular. However, many physicians have not fully exploited the properties of the electrodes in terms of battery current savings and the life achievable with programming pacemaker pulse voltages for safety margin levels above the threshold provided by these leads. .
Studies provided lower stimulation thresholds and improved sensing performance. And the performance and reliability of the continuous pacing lead were increased. One object of the present invention is to achieve a significantly lower stimulation threshold and to convince the physician of treatment with a lower voltage stimulation pacing pulse program.

The overall lead impedance consists of the electrode tips as well as the resistance of the lead wires, the effective impedance of the electrode-tissue interface. An inefficient way or means of increasing the impedance is to increase the resistance of the conductor. This wastes current as heat. It is desirable to reduce lead current consumption with more efficient control of electrode tissue interface impedance. This can be achieved by reducing the surface area of the cathode. However, it is generally believed that small electrodes are inefficient at sensing self-tuning depolarization of heart tissue. However, this is not always true. As measured on a high megohm range input impedance oscilloscope, the amplitude of the native cardiac depolarization signal (generally the ventricular QRS and / or atrial P-wave complex) is essentially independent of electrode size. I have. The problem is that the sensitivity amplifiers of modern pulse generators have a relatively low input impedance, typically 35 kΩ. The impedance (or electrode impedance) of the QRS or P-wave signal increases with decreasing electrode surface area. Therefore,
A 5 mm ² polished electrode will produce a QRS or P-wave with approximately 5 kΩ source impedance. According to Kirchhoff's law, the attenuation of the signal in the generator amplifier is 1 / (1 + Zin /
Zs). Zin is the input impedance of the amplifier. And Zn is the source impedance of the sensed signal. Therefore, the 5kΩ signal to the 35kΩ amplifier is 1 / (1 + 35 /
5) Reduce the amplitude to 12.5%. At a minimum,
This creates a difference between proper sensing and non-sensing. Therefore, it is important to keep the power source impedance low, and it is desirable not to attenuate the cardiac signal to less than 5%. That is, Zs for 35 kΩ amplifier
<1800Ω is desirable.

The need for low current consumption and sufficient sensing,
There is a correlation between the surface area of the cathode electrode.
In addition, a relatively low polarization effect can be achieved, evoking or distorting the electrogram of evoked or endogenous cardiac depolarization or incorrectly leaving the post-pulse potential large enough for the QRS by the amplifier. It is desirable not to be detected as a P wave.

DISCLOSURE OF THE INVENTION Accordingly, in order to increase the pacing impedance without increasing the threshold to a point well below currently recognized properties and without the force adversely affecting perception,
It is an object of the present invention to reduce the effective surface area of the pacing electrode.

The present invention provides a subcutaneously implantable lead for delivering an electrical stimulant to a desired body site, particularly the atrium or ventricle of a patient's heart. This lead was exposed about 1.
It has a geometric or microscopic surface area of 5 mm ^2, very high pacing impedance (800 ohms or more), showing a low peak and chronic thresholds, low source impedance and excellent sensitivity. In particular lead of the present invention, the exposed geometric surface area 0.1 to the 4.0 mm ^2, preferably in the range of from
Between 0.6 and 3.0 mm ² , about 1.0 mm ² has electrodes that give optimal performance. This lead has a pacing impedance of 1400 ± 260 ohms and a source impedance of about 1650 ± 410 ohms in both ventricles of the heart. The lead of the present invention constitutes a pacing lead, wherein a disk having a spherical, hemispherical or disk-like shape and a diameter of about 1 mm has an exposed distal tip electrode. The electrode is made of platinated porous platinum (or other porous electrode material)
And carries glucocorticosteroids.
In at least one embodiment, three or four electrodes are attached to the distal end of a pacing lead approximately 1.0 mm in diameter.

Endocardial and epicardial leads can also be made in accordance with the present invention.

In another embodiment of the present invention, DCD electrode technology may be employed by having a steroid-eluting release element and a hole of 0.1 to 4.0 mm ² .

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, as well as many advantages of the present invention will be better understood with the accompanying drawings and the following detailed description of the preferred embodiments. In the following, similar parts will be described with the same reference numerals.

FIG. 1 is a side view of an endocardial monopolar sphere-tip electrode pacing lead according to the present invention.

FIG. 2 is a cross-sectional view of the ball-tip electrode of the lead shown in FIG.

FIG. 3 is a plan view of the distal tip of the electrode of the lead shown in FIG.

FIG. 4 is a cross-sectional view of the distal portion of an endocardial monopolar DCD electrode pacing lead according to the present invention.

FIG. 5 is a plan view of the distal tip of the DCD electrode of the lead shown in FIG.

FIG. 6 is a cross-sectional view of the distal tip portion of another endocardial bipolar columnar tip electrode pacing lead according to the present invention.

FIG. 7 is a plan view of the distal tip electrode of the lead shown in FIG.

FIG. 8 is a cross-sectional view of a distal tip portion of another embodiment of the ball-tip electrode according to the present invention.

FIG. 9 is a sectional view of a modified example of the distal electrode of the DCD electrode according to the present invention.

FIG. 10 is a plan view of the distal portion of a bipolar epicardial pacing lead according to the present invention.

FIG. 11 is a cross-sectional view of the distal tip portion of the electrode preferably employed in the epicardial electrode of FIG.

FIG. 12 is a graph showing the performance of an exposed electrode of the present invention with steroid elution versus an electrode of the same size without steroid elution.

FIG. 13 shows DCDs of the invention with steroid elution versus reagent DCD electrodes of the same size without steroid elution.
4 is a graph showing the performance of an electrode.

DETAILED DESCRIPTION OF EMBODIMENTS Before describing specific features of the preferred embodiment of the present invention, certain items are defined. First, the practice of the present invention involves a structure that allows drug elution from the surroundings and / or through itself, and allows the body to contact the cellular foreign body or lead chip with electrodes to reach the endocardium or cardiomyocytes. Plan to use steroids or other drugs near the pacing lead tip to reduce acute and chronic inflammation caused by the inflammatory response of the electrodes, as described in the Stokes patent mentioned above. With or without a specific steroid elution pathway
It has a generally porous structure on either the electrode body or its surface. The exposed electrode used for the stimulating action has a relatively small surface area in overall dimensions and shape, but the surface area for sensing becomes large because the electrode surface and the electrode body are porous. That is, porous tissue exhibits a large surface area for stimulating and sensing in a microscopic sense, and a very small surface area in a macroscopic or geometric sense. Not only the porosity of the tissue, but also the prior art described above and U.S. Pat.Nos. 4,773,433, 4,819,661, 4,149,54
No. 2, No. 4,677,989, No. 4,819,662, No. 4,603,704,
No. 4,784,161, 4,784,160 and all the prior art disclosed preferred electrode materials and associated assembly techniques are employed to achieve a microporous structure.

Further, the present invention can be implemented in a conventional exposed electrode of the type shown in the aforementioned Parsonnet patent and an electrode structure referred to as a DCD electrode structure. It will be seen in the following description of the preferred embodiment that the electrodes of the present invention can be made to have the properties of both conventional and DCD electrode structures. Dr. Parsonnet worked to reduce the polarization overpotential (shown in the '116 patent Figure 2) and the resulting extrapulse extrapolation voltage, but found that the pulse extrapolation between 5 and 100 milliseconds after stimulant delivery. It was difficult to characterize the P or R wave of the heart from the voltage. In practicing the present invention, the electrodes are internalized in a DCD fashion or externalized in a conventional fashion. The macroscopic surface area through which the current released during the stimulus passes is defined by the pore area that appears in the tissue near the pacing lead tip. Figure 4 of the '116 patent
A large microscopic surface area is provided by the lead coil in the distal portion of the lead body, as shown at. In the present invention, the wire coil is woven or made porous by the techniques described above, and the steroid is eluted as described below.

FIG. 1 is a plan view of an exposed electrode according to the present invention. The lead includes a long lead body 10 covered by an insulating sleeve 12. The insulating sleeve 12 may be made of a flexible biocompatible and biostable insulator, especially silicone rubber or polyurethane. At the proximal end of the lead, a terminal assembly 14 connects the lead to a subcutaneously implantable pacemaker pulse generator. The terminal assembly 14 includes a known seal ring 16 and terminal pins 18. An anchoring sleeve 20 shown in partial cross section has a lead body 10
Slide in. The anchoring sleeve 20 serves in a known manner as a point for suturing the lead body to human tissue at the point of insertion of the lead into a blood vessel or tissue. The anchoring sleeve 20 and the terminal assembly 14 are preferably made of silicone rubber.

Further, the lead shown in FIG. 1 is a stylet guide.
11 and a stylet assembly 13. The stylet assembly 13 connects to terminal pins 18 for guarding the lead during transvenous insertion of the lead into the right ventricle or right atrium of the heart. Discard the stylet guide and stylet assembly after use. Then, before connecting the terminals, the terminal pins 18 are connected to the pacemaker pulse generator.

A tine protector 15 is shown at the distal end of the lead 10 to protect the tine until the lead is used. Tyne
26 is employed in a manner known in the pacing art to passively hold the tip electrode 22 to the endocardial location.

The lead assembly 10 of FIG. 1 includes a multi-stranded stranded conductor coil extending from the terminal pin 18 to the tip electrode 22. While FIG. 1 shows a monopolar lead, the present invention provides a distal tip electrode 22.
Also implemented as a bipolar lead using a second conductor exiting from a second exposed cylindrical terminal surface area near the proximal end of the lead to a known exposed annular electrode spaced at least 8 mm from it can. Current sensitive amplifier band center frequency is 25
Or 30 Hz, so an interval of 8 mm or more is required.
If the sensitivity amplifier band center frequency is shifted to higher values and gains higher, a smaller space is also possible.

FIG. 2 shows, in cross section, the distal lead portion of a preferred embodiment of the electrode of the present invention and the connection of that portion to the lead wire 28. In FIG. 2, the distal electrode 22 is shown as a porous platinum sphere covered by platinum black, and the lead electrode coil 22
Extends to the distal end of 28. The lead coil 28 is attached at the point 34 at the proximal end of the pin at the time of manufacture by swaging with a swaging member 36. Silicone adhesive may be used at site 32 to seal blood leaks into the lead coil.
The insulating sheath 12 is shown to be located on the swaging member as well as the tine assembly 38 and fits between the insulating sheath 12 and the distal end of the swaging member 54. An electrode ball is fitted on the tip of the steroid silicone rubber compound ring 40.

FIG. 3 shows the end faces of the ball-tip electrode 22, the tines 26, and the tines assembly 38. The ball-tip distal electrode 22
Made as shown in FIGS. 2 and 3, it has an annular, hemispherical or spherical exposed macroscopic surface area in the range of 0.1 to 4.0 mm ² . The ball-tip electrode 22 is 0.5 to 1 during the sintering process.
Made of porous sintered platinum using 00 micron porous "splat" powder.

A porous platinum electrode is electroplated with platinum black and a porous material to reduce power supply impedance and polarization with the platinum black coating. As loaded with an anti-inflammatory agent, the silicone backing sleeve 40 forms a monolithic controlled release element (MCRD) such as the steroid dexamethasone sodium phosphate. The steroid is finely divided into a porous platinum electrode 22 by supplying a solution of 200 mg U.SP dexamethasone sodium phosphate dissolved in 5.0 cc of isopropanol and 5.0 cc of distilled or deionized water as described in the Stokes patent described above. It is also deposited in the pores. The MCRD weight and composition as well as the electrode surface area determine the performance of the electrode. Electrodes of small geometric size in a macroscopic sense result in very high pacing impedance. The porous surface structure made of platinum black electroplating and steroids contributes to low polarization, low power source impedance and low threshold of a large surface area microscopically. The porous surface also facilitates steroid retention and platinum black adhesion to the electrode surface. 4 and 5 show a DCD electrode made in accordance with the teachings of the present invention. Platinated coil 50 made of platinum wire is caulked to wire coil 28 using caulking sleeve 52 and caulking core 58. Silicone rubber adhesive
54 can be used to provide a seal that prevents blood from leaking into the lead coil. The polymeric insulation tube 12 extends to or beyond the end of the platinized coil 50. Three or four symmetrically installed tines 26 are installed in close proximity to distal openings or holes 56. As shown, hole 56 in tube 12 has an annular hole of 0.1 to 4.0 mm ² , approximately 0.62 mm ² . The lumen of the platinated coil is filled with a solution of 200 mg dexamethasone sodium phosphate dissolved in 5 cc of water and 5 cc of isopropanol. The solvent evaporates leaving the steroid coating on the coil. . Steroid-loaded MCRD40 is located at the proximal end of the platinated coil. To produce a low polarization, the exposed surface of the platinated coil 50 is preferably
Must be at least 50 mm ² wide.

Past DCD electrodes have required that the distal lumen be filled with conductive saline prior to insertion into the vessel. . This is not required for steroid loaded leads. Allowing blood to fill the lumen as the lead pushes down the vessel,
This is because steroids work as infiltrants.

In operation, charge transfer from electrons to ions occurs between the platinated coil. Blood and fibrous tissue eventually fill the lumen. Since the surface on which this charge transfer takes place is large, the polarization loss is low. The current is directed through the blood and fibrous tissue to the myocardium to provide a stimulating effect. Since the hole 56 is small, the acute threshold is low and the pacing impedance is high. . Steroids control inflammation of surrounding tissues and prevent or reduce long-term threshold rise. 5 shows a variation of the bipolar endocardial pacing lead of the present invention. And especially, a modification of the electrode assembly of the present invention is shown. . The lead of FIG. 6 is made in a manner equivalent to the leads of FIGS. In these two lead embodiments, identical or similar parts are designated by the same reference numerals as much as possible. The main difference between FIGS. 1-3 and FIGS. 6 and 7 is that the leads of FIGS. 6 and 7 are bipolar with the annular electrode 60 spaced from the tip electrode 22 and the tine 26
Is somewhat different, and the four-turn coil 28 constitutes two pairs of commonly wound separately insulated conductors of two turns, each connected to two electrodes. is there.
Thus, at site 62, two wires are attached to ring electrode 60, and at site 64, the other two wires are pinned.
23 and swage sleeve 36 contact. Swaging sleeve 36
Is swaged against coil 64 at site 34. Pin 23
Extends through the steroid permeation ring 40. . The tip electrode 22 'is the tip electrode 2 of the embodiment of FIGS.
Made of the same material as 2 and used in the same manner. 6 and 7 illustrate a bipolar embodiment of a pacing lead of the present invention.

FIG. 8 shows another ball tip electrode 22 "attached to pin 23, with pin 23 extending in the opposite direction (not shown) to connect to a coiled wire conductor in the same manner as described above. The tip electrode 22 "is almost completely exposed, as is the distal end portion of the tip electrode. Thus, the electrodes shown in FIG. 8 may be employed in endocardial, epicardial or myocardial tip electrode leads that penetrate myocardial tissue, and are examples of the exposed microtip electrode limit of the present invention. Thus, the exposed surface of the MCRD 40 can elute steroids on both sides of the spherical electrode 22 ".

FIG. 9 shows yet another embodiment of the distal portion of the electrode of the present invention. The electrode of FIG. 9 is different from the electrodes shown in FIGS. 1 to 7 and is a modification of the electrode of FIG. The tip electrode 22 '''has been completely retracted into the distal portion of the tine carrying member 38. The internal diameter of the tine element 38, ie, the internal diameter of the lead tip, is preferably 1.016 mm (0.016 mm).
40 inches), the opening area is equal to 0.8 mm ^2. Ball electrode 2
Only the hemispherical portion of the 2 '''surface is exposed in this embodiment.

All of the above-described embodiments of the present invention are endocardial pacing leads, and the electrodes or lead tips are designed to reach or not reach the myocardium through the endocardium. Instead of the illustrated tine-based fixation structure, any of the endocardial lead embodiments also include an active screw-in fixation structure.

10 and 11 show yet another embodiment, in which the idea of the present invention is embodied as a bipolar epicardial pacing lead, in which the tip electrode 22 '''' penetrates the myocardium. For this purpose, it is mounted on a shaft 70 extending from a platform 72 of the epicardial lead body 74. Although not specifically shown, the epicardial lead of FIG. 10 is affixed in place by a securing hook or screw (partially indicated at 78) or by suturing.
The specific configuration of electrode 22 'is the same as any of the electrodes 22-22 described above, with the difference that the outer surface or tubular extension member 70 must be sufficiently rigid to allow the tip electrode to penetrate the epicardium. Further, for example, the above-mentioned Parsonne
It is understood that DCD designs of the type shown in the '116 patent can be used with the epicardial mold of the leads of the present invention.

However, preferably, tip electrode 22 and axis 70 are
Build as shown. Preferably the shaft 70 is a hollow metal tube
The MCRD 40 is located between the tip electrode 22 'and the portion in which the tube mechanically and electrically connects to a wire coil (not shown) within the housing 74. Tip electrode
22 'adheres to the tip of tube 80. The outer surface of the tube 80 is insulated by the mantle tube 12. Steroids in the MCRD 40 elute through the porous tip electrode 22 '.

The bipolar mesh electrode 76 shown in FIG.
', Soaked with steroids. The epicardial lead may also be made in a monopolar alternative to porous tissue for the metallic mesh electrode 76 to allow it to be anchored to the pericardium by ingrowth of fibrous tissue. The monopolar lead can be secured to the heart by suturing without the need for a tissue mesh. One such lead is Medtroni
c, U.S. Pat. No. 4,010,758, and such a lead is described in a paper by K. Stokes, "Preliminary Study of Novel Steroid-eluting Epicardial Electrodes" (PACE,
Vol. 11, November 1988, pp.1797-1803).

Each of the electrodes of the preceding embodiment may be a platinum splat which is coated with a machined electrode blank or by dipping the ends of the pins 23 of FIGS. 1-3 and 6-10 into a binder and adhering to the pins 23 in a generally spherical shape. Made by dipping a little into a fluidized bed of powder and sintering the powder.
The electrode of FIG. 11 is made by applying a mixture of binder and splat flour to the opening of tube 80 and sintering it in place.

The above-described embodiment of the present invention schematically shows the structure and characteristics of the very small diameter tip electrode and pacing lead of the present invention. In the prior art as described above, even lower limit for effective macroscopic surface areas, 5.5 mm ² and 8m
It is believed to exist between the m ^2. Our steroid-free work on small macroscopic surface area porous electrodes, both exposed and DCD configurations, confirmed the prior art expectations and findings described above.

When comparing the electrode without steroid with the exposed electrode of the present invention with steroid, the difference in the stimulus threshold is significant. Figure
12 shows the results of two studies of microleads with and without steroids attached to a dog's ventricle over 8 weeks.
The stimulatory threshold of the lead without steroid shows a marked increase compared to the lead with steroid.

 The actual data for this study is shown in Tables I and II below.

In our study without steroids, 0.1-0.2 mm ²
It has been found that DCD electrodes with holes of greater than or less than 0.5 mm ² will probably not work. They go to the exit block and stay there. As shown in the graph of FIG. 13, the DCD electrode with 0.6 mm ² holes without steroid shows a threshold rise from 0.5 volts to over 8 volts in 3 weeks. However, in the presence of steroid, as shown by the lower curve in FIG.
The D electrode is approximately 0.5 volts to approximately
Shows a periodic threshold rise to 0.8 volts.

Regarding the performance of the DCD electrodes, data from studies performed on dogs are shown in Tables III and IV below.

Thus, the micro-exposure and DCD electrodes of the present invention meet the desirable properties described above for pacing leads, with low stimulation thresholds, very high pacing impedances (800
It has been found that it has a relatively low polarization, is suitable for excellent sensing, and exhibits a reasonably low source impedance. The high pacing impedance increases the life of the pacing pulse generator and allows for component miniaturization. A low threshold allows a large safety factor at low applied voltages that also contributes to increased battery life.

Although embodiments of the present invention have been described for cardiac pacing applications, the present invention is applicable to other electrode technologies, including neurological and muscle stimulating applications where the above-described properties are desired. Further, the miniaturization of the electrodes provided by the present invention allows the stimulating / sensing leads to integrate two or more electrode structures on the tip of the probe. Although not specifically shown, the invention may be practiced with a tip electrode arrangement for providing actually closely spaced bipolar stimulation and sensing as illustrated in U.S. Pat.No. 4,662,382 to Sleutz et al. .

While the preferred embodiment of the invention has been described in detail with particular reference, it should be understood that various modifications can be made within the scope of the appended claims.

────────────────────────────────────────────────── (56) References US Patent 4,506,680 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61N 1/365 A61N 1/04

Claims (15)

(57) [Claims] 1. A lead subcutaneously implanted at a desired location in a human body, the implantable location being stimulable and sensible, comprising: (a) an electrical lead having a proximal end and a distal end; and (b) the proximal end. (C) electrical connector means for connecting to a proximal end of the electrical conductor for connection to a pulse generator; and (d) the electrical connector. It is electrically connected to the distal end of the conducting wire to transmit electrical energy to and from the human body tissue cells, stimulates and senses the implanted site, and provides 3.0 m to body fluids and tissues of the human body.
electrode means for exposing a portion having a surface area in a macroscopic sense of less than m ² , wherein (e) said electrode means is microscopic in proportion to the surface area in a macroscopic sense of said exposed portion A body of porous metal or other conductive material having a surface area in a sense, and provided at the distal end of the electrical conductor and having a proximal end at the distal end of the electrical conductor. (F) a drug dispensing means for dispensing a drug to a human body for reducing an undesired interaction with a human body around the pin, wherein the electrode is provided while storing the drug; A lead for stimulating and sensing a human body, wherein the lead is administered to the human body from a porous body of the means. 2. The body of the drug dispensing means is comprised of a water-permeable polymer, is located within the insulating sheath means, and is adjacent to the exposed portion of the electrode means containing the drug in a water-soluble form. 1 lead. 3. The lead of claim 1, wherein said drug is an anti-inflammatory drug. 4. The lead of claim 4, wherein said drug is the sodium salt of dexamethasone phosphate. 5. The lead of claim 1, wherein the surface area of the electrode in the macroscopic sense is in the range of 0.10 to 4.0 mm ² . 6. The lead according to claim 1, wherein the surface of the exposed portion of said electrode means has a substantially hemispherical shape. 7. The lead of claim 1 wherein said drug dispensing means is located corresponding to said porous portion for delivering said drug to human tissue through said porous portion. 8. A cardiac pacing implant for subcutaneous implantation at a desired location in a patient's body for a prolonged period of time to provide a desired cardiac stimulation and sensing lead having (a) a proximal end and a distal end. (B) insulating sheath means for covering the conductor between the proximal end and the distal end; (c) electrical connection to the proximal end of the conductor for connection to a pulse generator. Connector means, (d) electrically connected to the distal end of the electrical lead to transfer electrical energy to and from human body tissue cells, stimulate and sense the implanted site, and 3.0m
electrode means for exposing a portion having a surface area of at macroscopic sense less than m ^2, (e) the insulating sheath means in the electrode connecting means for electrically connecting the distal end of said electrical lead to said electrode means, (F) the electrode, located within the insulating sheath means and at least partially near the electrode means and the electrode connection means, and storing a drug to reduce undesired interactions with the human body; (H) a drug delivery means connected to the drug delivery means and delivering the drug to heart tissue of a human body; An electrode means having a body of porous metal or other conductive material having a microscopic surface area proportional to the macroscopic surface area of the exposed portion, and At the distal end of the conductor A drug dispensing means for dispensing a drug for reducing undesired interaction with the human body, the drug being supplied to a conductive pin having a proximal end connected to a distal end of the electrical wire; A lead for stimulating and sensing a human body, wherein the lead is provided around the pin, and the medicine is stored and dispensed to the human body from a porous main body of the electrode means. 9. The lead of claim 1 wherein the body of the drug dispensing means is comprised of a polymer, located within the insulating sheath means, and adjacent to an electrode containing the drug in a water soluble form. 10. The lead according to claim 1, wherein said drug is a water-soluble anti-inflammatory drug. 11. The lead of claim 10, wherein said drug is the sodium salt of dexamethasone phosphate. 12. The lead of claim 10 wherein said electrode means comprises a length of conductive wire connected at one end to a distal end of said electrical lead. 13. The lead according to claim 12, wherein said conductive wire has platinum black on an exposed surface thereof. 14. The method according to claim 14, wherein the exposed surface of the conductive wire is
14. The lead according to claim 13, formed of porous platinum. 15. The lead of claim 8, wherein said exposed surface of said electrode means within said insulating sheath means is approximately 50 mm ² .