Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-02-24
2003-03-18
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S122000
Reexamination Certificate
active
06535762
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable cardiac stimulation devices and, more particularly, to a simplified implantable lead for a combination implantable cardioverter/defibrillator (ICD) with bradycardia support pacing system adapted to transmit electrical signals using an improved distal end portion of the lead, the distal end performing shocking, pacing and sensing functions using a single electrode.
BACKGROUND OF THE INVENTION
A depolarization signal (a small electrical impulse) is generated by most muscle tissue as such tissue contracts. Thus, the beating or contracting of a human heart is manifest by appropriate depolarization signals evidencing: the contraction of the atria, referred to as the P-wave, and the contraction of the ventricles, referred to as the R-wave (or the QRS complex). The sequence of P-waves followed by R-waves thus comprises an electrogram or electrocardiogram signal that can be monitored by appropriate electrical circuits to indicate the status of the heart.
An implantable pacemaker includes sensing circuits that monitor the heart by looking for the occurrence of P-waves and/or R-waves, and pacing circuits that stimulate the heart with an appropriate electrical stimulation pulse in the event that a depolarization signal is not sensed within a prescribed time period. In this way, if the heart does not beat naturally within the prescribed time period, then an electrical stimulation pulse is provided to force the heart muscle tissue to contract, thereby assuring that the prescribed minimum heart rate is maintained.
An implantable cardioverter-defibrillator (ICD) typically includes sensing and pacing circuits to provide electrical stimulation pulses aimed at responding to slow intrinsic (natural) cardiac rates or asystole (a non-beating heart). The pacing circuits may also provide appropriate electrical stimulation pulses, typically in a prescribed burst or pattern, aimed at terminating rapid intrinsic rates (tachyarrhythmias or tachycardias).
With any bioelectric stimulation device, it is essential to determine accurately the ability of that device to accomplish the task for which it was designed. If nature were truly constant, and in-finitely small steps were used, theoretically it would be possible to define a limit, or threshold, below which no activation would occur and above which activation would occur 100% of the time (see FIG.
1
A). In biological systems, such constancy is not possible. Instead, a balance point is the norm, at which activation occurs 50% of the time (E50 shown in FIG.
1
B).
In addition, even with all external variables constant, there remains the inherent problem of biovariability, both subject-to-subject and time-dependent, thus yielding a sigmoidal-shaped curve (
FIG. 1B
) for finding the probability of success of a stimulus. For the investigator working with implantable defibrillators, variability is abundant, with some variables determinable, but most not, as they appear to vary either “randomly” or “chaotically.” Despite major design improvements and mathematical expertise in the last two decades, our ability to understand the mechanisms of this variability has changed little since the classical experiments performed in the 1930s. Nevertheless, there have been several attempts to accurately assess defibrillation efficacy within a reasonable window of probability (also called the probability of success curve for defibrillation).
It is important to recognize that there is variation in the probability of any system to defibrillate at a particular instant in time (FIG.
1
B). The spectrum of factors which may contribute to this variability are poorly understood. For example, the same setting on a defibrillator will fail on one attempt but be successful a few seconds later, with no obvious change in any measured variable.
There has been some suggestion that the mechanisms which alter efficacy due to the stochastic processes might be “random” or “chaotic”. Although this has not been resolved, it seems implicitly clear that, as myocytes are not instantaneously depolarized and spontaneously repolarized, once a particular wave pattern of activation is established (at a given interval in time), in the next several milliseconds the pattern cannot be truly random since, to be truly random, all myocytes must have an equal chance of being reactivated. Clearly, those which are totally depolarized or are in the early phases of the activation will be in a refractory state and will not be reactivatable. Thus, for the subsequent several milliseconds, the movement of the wavefront(s) cannot be random. Therefore, although the tenant of randomness remains possible for the pattern in the first instant selected, a second selection within a short period of time thereafter cannot be random. Also, there may be some factors that influence defibrillation which are determinable.
The previous theory applies to atrial and ventricular defibrillation.
An ICD must perform at a minimum sensing, pacing, and defibrillation. Common ICDs use a multitude of electrodes to sense/pace and defibrillate. However the conventional approach, with dedicated electrodes for defibrillation, pacing, and sensing result in a complex, large lead body (greater than ~10 F). The large size of the lead results mainly because of insulation between the different conductors. In addition, due to the presence of a pacing dipole at the tip of a conventional lead, the defibrillation coil may be 2 cm away from the apical area when used in the right ventricle. This results in a low potential gradient near the apex and causes higher defibrillation thresholds.
Typical of the prior art in this regard, the following U.S. patents all disclose endocardial leads used for both sensing and pacing:
Pat. No.
Inventor(s)
Issued
5,571,157
McConnell
Nov. 5, 1996
5,267,564
Barcel et al.
Dec. 7, 1993
4,848,352
Pohndorf et al.
July 18, 1989
4,592,372
Beranek
June 3, 1986
Each of the following U.S. patents discloses an electrode assembly for an implantable lead:
Pat. No.
Inventor(s)
Issued
5,571,158
Bolz et al.
Nov. 5, 1996
5,181,526
Yamasaki
Jan. 26, 1993
5,097,843
Soukop et al.
Mar. 24, 1992
4,325,389
Gold
Apr. 20, 1982
and the patents to Soukop et al., Yamasaki, and Bolz et al. specifically disclose porous electrode constructions for increasing the effective surface area of the electrode. It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.
SUMMARY OF THE INVENTION
The present invention relates to an implantable stimulation system and lead which is adapted to transmit electrical signals between a return electrode and an “integrated” distal electrode capable of providing pacing pulses and shocking pulses, as needed, to stimulate selected body tissue, in addition to receiving cardiac signals. Whereas the prior art required separate electrodes for pacing/sensing, shocking, the present invention advantageously integrates all these functions into a single electrode, significantly simplifying the lead's construction.
Although the previous background material is directed towards ventricular defibrillation, the same principles of the invention can be applied to atrial defibrillation.
The present invention is compatible with an implantable cardioverter defibrillation (ICD) device, which includes circuitry for sensing intrinsic depolarization signals of the patient's heart, first and second stimulating circuitry for generating electrical pacing pulses and defibrillation pulses, respectively, and transmitting such pulses to the patient's heart, and an electrically conductive enclosure (i.e., the housing or “case” electrode) protectively supporting and encompassing the sensing circuitry, and the first and second stimulating circuitry.
The present invention is directed towards an improved implantable lead having a single biocompatible electrode at the distal end of the lead which engages with the body tissue in the right ventricle of the patient's heart. The implantable le
Pacesetter Inc.
Schaetzle Kennedy
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