Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-04-26
2003-01-28
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06512953
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a programmable cardiac stimulating apparatus for the purpose of automatically verifying capture during multi-chamber stimulation. More specifically, the present invention is directed to an implantable stimulation device and associated method for automatically verifying simultaneous capture during bi-ventricular or bi-atrial stimulation, also referred to herein as bi-chamber stimulation or two corresponding chamber stimulation.
BACKGROUND OF THE INVENTION
Congestive heart failure (CHF) is a debilitating, end-stage disease in which abnormal function of the heart leads to inadequate blood flow to fulfill the needs of the body's tissues. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately fill with blood between heartbeats and the valves regulating blood flow may become leaky, allowing regurgitation or back flow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness, and inability to carry out daily tasks may result.
Not all CHF patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive.
As CHF progresses, it tends to become increasingly difficult to manage. Even the compensatory responses it triggers in the body may themselves eventually complicate the clinical prognosis. For example, when the heart attempts to compensate for reduced cardiac output, it adds muscle causing the ventricles to grow in volume in an attempt to pump more blood with each heartbeat. This places a still higher demand on the heart's oxygen supply. If the oxygen supply falls short of the growing demand, as it often does, further injury to the heart may result. The additional muscle mass may also stiffen the heart walls to hamper rather than assist in providing cardiac output.
CHF has been classified by the New York Heart Association (NYHA). Their classification of CHF corresponds to four stages of progressively worsening symptoms and exercise capacity from Class I to Class IV. Class I corresponds to no limitation wherein ordinary physical activity does not cause undue fatigue, shortness of breath, or palpitation. Class II corresponds to slight limitation of physical activity wherein such patients are comfortable at rest, but where ordinary physical activity results in fatigue, shortness of breath, palpitations, or angina. Class III corresponds to a marked limitation of physical activity wherein, although patients are comfortable at rest, less than ordinary activity will lead to symptoms. Class IV corresponds to inability to carry on any physical activity without discomfort, wherein symptoms of CHF are present even at rest and where with any physical activity, increased discomfort is experienced.
Current standard treatment for heart failure is typically centered around medical treatment using ACE inhibitors, diuretics, and digitalis. It has also been demonstrated that aerobic exercise may improve exercise tolerance, improve quality of life, and decrease symptoms. Only an option in approximately 1 out of 200 cases, heart transplantation is also available. Other cardiac surgery is also indicated for only a small percentage of patients with particular etiologies. Although advances in pharmacological therapy have significantly improved the survival rate and quality of life of patients, patients in NYHA Classes III or IV, who are still refractory to drug therapy, have a poor prognosis and limited exercise tolerance. Cardiac pacing has been proposed as a new primary treatment for patients with drug-refractory CHF.
By tracking the progression or regression of CHF more closely, treatments could be administered more effectively. Commonly, patients adapt their lifestyle and activities to their physical condition. The activity level of the patients with NYHA Class III or IV would be much lower than that of the patients with NYHA Class I or II. The change in lifestyle or activity level, due to the patient's heart condition, will be reflected by activity and respiration physiological parameters.
Besides various assessments of the cardiac function itself, assessment of activity and respiration are typically performed. This includes maximal exercise testing in which the heart rate and maximum ventilation are measured during peak exertion. However, peak exercise performance has been found to not always correlate well with improvements in a patient's clinical conditions. Therefore, sub-maximal exercise testing can also be performed, such as a six-minute walk test. While improvements in sub-maximal exercise may suggest an improvement in clinical condition, sub-maximal exercise performance can be variable in that it is dependent on how the patient happens to be feeling on the particular day of the test.
As CHF progresses, the dilation of the heart chambers alters the normal conduction time of the electrical signals through the heart. These electrical signals coordinate the depolarization and subsequent contraction of the heart chambers. Bi-ventricular pacing is expected to improve the coordination of heart chambers by reducing the right ventricle (RV) contraction time and the left ventricle (LV) contraction time, and by increasing the diastolic filling time.
One challenge in bi-ventricular pacing is the ability to detect and verify capture of both ventricles. Since the benefit of bi-ventricular pacing is derived only when capture of both chambers is achieved, proper determination of pacing threshold for each ventricle, or both combined, is imperative to a successful therapy delivery. During device implantation, physicians often rely on ECG recordings to observe when a stimulating pulse is of sufficient energy to cause heart contraction, a condition known as “capture.” The lowest stimulation pulse energy sufficient to capture the heart is referred to as “capture threshold.”
FIGS. 3A
,
3
B and
3
C depict three surface ECG recordings for three exemplary capture situations during bi-ventricular pacing.
FIG. 3A
represents a surface ECG recording during sub-threshold bi-ventricular pacing, and illustrates the failure to capture both the left and right ventricles.
FIG. 3A
shows a stimulation pulse
120
followed by a natural depolarization complex
124
, with a time delay
125
therebetween. In
FIG. 3A
neither ventricle is captured, and the intrinsic responses of both ventricles are represented by the depolarization complex
124
.
FIG. 3B
represents a surface ECG during bi-ventricular pacing in which the capture of only one ventricle (i.e., the right ventricle) but not the other ventricle (i.e., the left ventricle) is achieved. A ventricular stimulation pulse
126
is followed immediately by a depolarization complex
127
which is a complex representing both the evoked response of the captured ventricle and the intrinsic response of the other ventricle that has not been captured. The evoked response to the stimulation pulse
126
in one ventricle is conducted naturally to the other ventricle causing a second depolarization. The conducted response of the other ventricle slightly lags the evoked response in the captured ventricle in accordance with the inter-ventricular conduction delay. This slight delay, however, is not distinguishable on the surface ECG. Since two distinct events are not easily discernible, recognition of only single-chamber capture versus bi-ventricular capture from the ECG recording alone is quite difficult.
FIG. 3C
represents a surface ECG during bi-ventricular pacing when successful capture of both ventricles is achieved. A stimulation pulse
128
is followed immediately by a depolarization complex
129
representing the evoked response of both ventricles. This ECG recording appears generally similar to the ECG recording of
FIG. 3B
in which only one chamber was captured. As a result, differentiation between single-chamber capture (
FIG. 3B
) and bi-ventricular capture (
FIG. 3C
Bornzin Gene A.
Bradley Kerry
Florio Joseph J.
Park Euljoon
Getzow Scott M.
Pacesetter Inc.
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