Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-03-12
2002-10-08
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S017000
Reexamination Certificate
active
06463324
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to cardiac therapeutic devices, and specifically to cardiac pacemakers.
BACKGROUND OF THE INVENTION
The heart is a muscular pump whose mechanical activation is controlled by electrical stimulation generated at the right atrium and passed to the entire heart. In a normal heart the electrical stimulation originates as action potentials in a group of pacemaker cells lying in a sino-atrial (SA) node in the right atrium. In certain heart diseases, either congenital or acquired, natural pacing is replaced or assisted by artificial pacing induced by an implanted pacemaker. Pacemakers known in the art provide artificial excitatory pulses to the heart tissue, to control the heart rhythm.
Cardiac output, i.e., the output of the heart per unit time, is the product of stroke volume and heart rate. Hence, variations in cardiac output can be produced by changes in cardiac rate or stroke volume. The stroke volume can be influenced, for example, by changing the efficacy of cardiac contraction, by changing the length of the cardiac muscle fibers, and by changing contractility of cardiac muscle independent of fiber length. The heart rate and rhythm influence the cardiac output both directly and indirectly, since changes in the rate and rhythm also affect myocardial contractility.
The human body normally regulates the cardiac output in response to physiological needs, mainly by changing the heart rate, as during physical exercise, and/or by adapting the stroke volume. Under pathological conditions, however, some of the regulatory mechanisms may be damaged.
Artificially paced hearts typically lose more than 30% of their normal cardiac output, presumably due to loss of efficient contraction under artificial, as opposed to natural, electrical stimulation. In the context of the present patent application, this reduction is referred to as pacing-induced cardiac output (PICO) loss.
Moreover, when pacing is indicated, it is frequently in the wake of heart disease, particularly ischemic heart disease (IHD), including cases of myocardial infarction (MI), which in itself reduces the cardiac output. Such reduction is referred to in the context of the present patent application as global cardiac output (GCO) loss.
While electronic pacemakers can increases cardiac output temporarily by increasing the heart rate, this increase is at the expense of greater energy expenditure by the heart muscle, which the heart disease patient cannot generally sustain. Although modern pacemakers may include stimulation at two or more points and allow optimization of the excitatory pulse amplitudes, rate and timing, they do not address directly the loss of cardiac output caused by the pacing, nor do they address the loss due to cardiac pathology. These losses are mainly related to reduction in the stroke volume, which cardiac pacing tends to exacerbate. Defibrillators are useful in treating arrhythmia when it occurs (although they are painful to the patient and traumatic to the heart), but they provide no long-term amelioration of cardiac insufficiency. Thus, none of the treatments known in the art allow effective, long-term regulation of cardiac output, because they are aimed at controlling the heart rate and do not address the need to increase the stroke volume and the efficiency of contraction of the heart.
The electromechanical properties of the heart, as well as methods known in the art for influencing these properties, are more fully described in the “Background of the Invention” section of PCT patent application PCT/IL97/00012, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference.
SUMMARY OF THE INVENTION
The inventors have found that by applying non-excitatory electrical stimulation pulses to cardiac muscle segments, appropriately timed with respects the heart's electrical activation, it is possible to regulate the cardiac output.
It is therefore an object of the present invention to provide devices that allow both artificial heart pacing and effective regulation of cardiac output, and particularly devices that increase the cardiac output by enhancing the heart's stroke volume.
The present invention thus provides thus provides apparatus for heart pacing with cardiac output regulation, including one or more implantable electrodes, which apply electrical signals to cardiac muscle segments, and signal generation circuitry, which applies an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart and a non-excitatory stimulation pulse to at least one of the one or more electrodes to regulate the cardiac output.
Another aspect of the present invention relates to a method for heart pacing with cardiac output enhancement, including implanting one or more electrodes in a subject's heart; applying an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart; and applying a non-excitatory stimulation pulse to at least one of the one or more electrodes to regulate an efficacy of cardiac contraction.
The term “non-excitatory electrical stimulation”, in the context of the present patent application and in the claims, refers to electrical pulses that do not induce new activation potentials to propagate in cardiac muscle cells. Rather, such pulses affect the response of the heart muscle to the action potentials, by modulating cell contractility within selected segments of the cardiac muscle. Specifically, as described in the above-mentioned PCT patent application PCT/IL97/00012 and incorporated herein by reference, the inventors have found that by applying non-excitatory electrical stimulation pulses of suitable strength, appropriately timed with respect to the heart's electrical activation, the contraction of the selected segments can be increased or decreased, thus increasing or decreasing the stroke volume of the heart. This finding forms the basis for the present invention.
According to preferred embodiments of the present invention, the non-excitatory stimulation pulse is coupled to the activity of a pacemaker, and in various embodiments, the non-excitatory stimulation pulse is synchronized by pacing pulses generated by the pacemaker. In other embodiments of the present invention, one or more sensors are provided in the apparatus to sense local activity in the heart tissue, to enable the non-excitatory stimulation pulse to be triggered independently of the pacemaker, particularly when the pacemaker is inactive for a period of time, as is known in the art, for example, with regard to VVI and DDD pacemakers.
In preferred embodiments of the present invention, a cardiac output enhanced pacemaker (COEP) comprises a pacing unit and a non-excitatory stimulation unit. The pacing unit provides pacing pulses to the heart muscle for controlling the heart rate, as is known in the art. The non-excitatory stimulation unit provides stimulation pulses to at least a segment of the heart muscle, synchronized with the pacing pulses, so as to enhance the response of the muscle to the pacing pulses, preferably to increase the heart's stroke volume. Each of the two units comprises one or more electrodes to be implanted in a subject's heart and signal generation circuitry coupled thereto. The circuitry is preferably encased in an implantable case, similar to those used in pacemakers known in the art, and preferably uses a similar type of battery as a power source.
Thus, in preferred embodiments of the present invention, the COEP device applies both excitatory electrical stimulation, to pace the heart by generating activation potentials in the cardiac muscle tissue, a non-excitatory stimulation, to control response of the muscle to the activation potentials. In this respect, the device differs fundamentally from pacemakers and other implantable cardiac electronic devices known in the art, which provide only excitatory stimulation. When the COEP is used to pace the heart, the activation of the heart with respect to the pac
Ben-Haim Shlomo
Darvish Nissim
Fenster Maier
Mika Yuval
Impulse Dynamics N. V.
Jastrzab Jeffrey R.
Reed Smith LLP
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