Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-01-14
2001-09-25
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S005000
Reexamination Certificate
active
06295470
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable cardioverter/defibrillator with antitachycardial pacing capabilities and/or a method of such pacing.
BACKGROUND OF THE INVENTION
The typical implantable cardioverter/defibrillator (ICD) delivers an initial electrical countershock within ten to twenty seconds of arrhythmia onset, thereby saving countless lives. Improved devices have antitachycardia pacing capabilities in addition to cardioverting/defibrillating functions. These ICDs are capable of different initial responses to one or more tachycardia as well as a programmable sequence of responses to a particular arrhythmia.
The output energy level is generally set by a physician in accordance with a patient's capture threshold, determined at the time of heart implantation. This threshold represents the minimum pacing energy required to reliably stimulate a patient's heart. However, due to trauma associated with the stimulation, scar tissue grows at the interface between the implanted cardiac pacer leads and the myocardium. This scar tissue boosts the patient's capture threshold. To insure reliable cardiac capture, the output energy level is thus generally set at a level which is a minimum of two times greater than the initially measured capture threshold. A drawback to such an approach is that the higher stimulation level causes more trauma to the cardiac tissue than would a lower level of stimulation, and hence promotes the formation of scar tissue, thereby boosting the capture threshold.
The higher stimulation level also shortens battery life. This is not desirable, as a shorter battery life necessitates more frequent surgery to implant fresh batteries.
Another drawback is the potential for patient discomfort associated with this higher stimulation level. This is because the higher stimulation level can stimulate the phrenic or diaphragmatic plexus or cause intercostal muscle pacing.
Lastly, the higher stimulation is less effective, due to entry block.
A need therefore exists for an ICD that can achieve reliable cardiac capture with a lower stimulation level, thereby causing less damage to the heart, extending battery life, causing less pain to the patient and having greater therapeutic effectiveness than current ICDs. A need also exists for an ICD that can better entrain the heart and can entrain portions of the heart from a greater distance.
SUMMARY OF THE INVENTION
It therefore is an object of the present invention to provide an ICD with antitachycardial pacing capabilities, wherein the stimulation is administered with a voltage either at, just above, or just below the diastolic depolarization threshold potential.
It is another object of the present invention to sense whether cardiac capture has occurred, and if not, to administer additional stimulation.
It is another object of the present invention to provide the additional stimulation at a slightly higher voltage level than that level of stimulation which resulted in no capture.
It is another object of the present invention to repeat the stimulation—sensing cycle until cardiac capture has occurred.
It is another object of the present invention to provide stimulation using a biphasic waveform.
The present invention accomplishes the above objectives by providing an implantable cardioverter-defibrillator with a unique constellation of features and capabilities. Protocols disclosed include:
1/biphasic stimulation administered at, or just above, the diastolic depolarization threshold potential;
2/biphasic or conventional stimulation initiated at, or just above, the diastolic depolarization threshold potential, reduced, upon capture, to below threshold; and
3/biphasic or conventional stimulation administered at a level set just below the diastolic depolarization threshold potential.
As mentioned, the antitachycardial pacing protocols of the present invention can be used in conjunction with biphasic pacing. The method and apparatus relating to biphasic pacing comprises a first and second stimulation phase, with each stimulation phase having a polarity, amplitude, shape, and duration. In a preferred embodiment, the first and second phases have differing polarities. In one alternative embodiment, the two phases are of differing amplitude. In a second alternative embodiment, the two phases are of differing duration. In a third alternative embodiment, the first phase is in a chopped wave form. In a fourth alternative embodiment, the amplitude of the first phase is ramped. In a fifth alternative embodiment the first phase is administered over 200 milliseconds after completion of a cardiac beating/pumping cycle. In a preferred alternative embodiment, the first phase of stimulation is an anodal pulse at maximum subthreshold amplitude for a long duration, and the second phase of stimulation is a cathodal pulse of short duration and high amplitude. It is noted that the aforementioned alternative embodiments can be combined in differing fashions. It is also noted that these alternative embodiments are intended to be presented by way of example only, and are not limiting.
Enhanced myocardial function is obtained through the biphasic pacing of the present invention. The combination of cathodal with anodal pulses of either a stimulating or conditioning nature, preserves the improved conduction and contractility of anodal pacing while eliminating the drawback of increased stimulation threshold. The result is a depolarization wave of increased propagation speed. This increased propagation speed results in superior cardiac contraction leading to an improvement in blood flow and in increased access to reentrant circuits. Improved stimulation at a lower voltage level also results in reduction in scar tissue buildup thereby reducing the tendency of the capture threshold to rise; reduction in power consumption leading to increased life for pacemaker batteries; and decreased pain to the patient.
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Getzow Scott M.
Roberts Abokhair & Mardula LLC
The Mower Family CHF Treatment Irrevocable Trust
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