Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-03-12
2001-10-02
Jastrzab, Jeffrey R. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06298268
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to cardiac therapeutic devices, and specifically to invasive devices for enhancing performance of the heart.
BACKGROUND OF THE INVENTION
Cardiac insufficiency, characterized inter alia by a reduction in the cardiac output, is a common, well-known and well-documented heart malfunction. It develops as a result of congenital defects or as an end-effect of many diseases. 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 chances in cardiac rate or stroke volume. The stroke volume can be influenced, for example, by changing the strength 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 body needs by changing the heart rate, as during physical exercise, and/or by adapting the stroke volume. Under pathological conditions, however, some of the normal regulatory mechanisms may be damaged. For example, heart tissue damaged due to myocardial infarct typically cannot sustain normal pumping function, leading to a reduction in stroke volume, and hence of cardiac output. The body may react to such a reduction by increasing the heart rate, thus imposing long term strain on the heart muscles, leading in more severe cases to heart failure. There is thus a need for devices and treatments that can regulate the cardiac output, so as to compensate for the deficiencies in the normal regulation mechanisms.
In response to this need, modern cardiology has developed means to control various parameters associated with the heart's operation. Pharmaceuticals, for example, may be used to influence the conduction velocity, excitability, contractility and duration of the refractory period of the heart tissue. These pharmaceuticals are used to treat arrhythmia, enhance cardiac output and prevent fibrillation. Pharmaceuticals are generally limited in effectiveness in that they affect both healthy and diseased segments of the heart, usually, with a relatively low precision. They frequently also have unwanted side-effects.
A special kind of control can be achieved using implantable electronic devices, which provide excitatory electrical stimulation to the heart to control directly the heart rate and/or rhythm. For example, a pacemaker, an electronic devices which is typically implanted in the heart to support the heart's electrical excitation system or to bypass a blocked portion of the conduction system. Another type of cardiac electronic device is a defibrillator, which senses fibrillation in the heart and applies a high voltage impulse to “reset” the heart. While electronic pacemakers can control the heart rate, however, they are limited in their capacity to enhance cardiac output, and they are known to reduce stroke volume in at least some instances. 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. 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 is incorporated herein by reference.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a device and method for regulation of hemodynamic parameters, and particularly for increasing the cardiac output by enhancing the heart's stroke volume.
In preferred embodiments of the present invention, a cardiac output controller comprises a non-excitatory stimulation probe, including one or more non-excitatory stimulation electrodes; at least one sensor, preferably a sensing electrode; and electronic control circuitry, coupled to the stimulation probe and sensor. The stimulation electrodes and, preferably, the sensor are implanted in the heart of a subject. Alternatively, a sensing electrode may be placed on a body surface. The circuitry receives signals from the sensor, indicative of the heart's activity, and responsive thereto, drives the stimulation electrodes to provide non-excitatory electrical stimulation to the heart.
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 generally affect the response of the heart muscle to the action potentials, possibly 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.
In preferred embodiments of the present invention, characteristics of the non-excitatory stimulation are adjusted so as to modify the heart's muscular activity, thus affecting the cardiac output, preferably by increasing the stroke volume, without directly affecting the heart rate. Preferably, the device is used to increase cardiac output substantially continuously for extended periods of time, most preferably to boost cardiac output during those portions of a day for which a patient needs increased blood supply. Accordingly, the device is preferably not used at night, to allow the heart muscle to rest.
Alternatively, the device may be used to modify the heart's muscular activity in other ways. For example, in some conditions, such as HOCM (hypertrophic obstructive cardiomyopathy), the device may be operated to reduce cardiac output, so as to reduce the workload on the heart, or particularly to reduce cardiac muscle contraction in a hypertrophic region of the heart. As another example, the device may be used to increase the heart's contraction efficiency, so that a given level of cardiac output is maintained at a reduced expenditure of energy. Such uses of the device are described further in a PCT patent application entitled, “Apparatus and Method for Controlling the Contractility of Muscles,” filed on even date (Ser. No. 09/254994, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference.
In any case, the effect of the device on cardiac output is preferably regulated by changing the timing of the non-excitatory stimulation pulse relative to the heart's activity, preferably relative to the heart's local electrical activity or ECG signals received by the sensing electrode, and/or by changing other pulse characteristics, such as the voltage, current, duration, polarity, waveform and frequency of the waveform. Preferably, the device senses the heart's sinus rhythm and applies and synchronizes the stimulation pulse relative thereto, preferably with a delay before the onset of the stimulation pulse. Additionally, the circuitry may analyze the signals, for example, to determine the QT interval, so as to adjust the stimulation pulses responsive thereto. Alternatively, when the heart's rhythm is irregular, due to ventricular premature beats (VPB's) or other cardiac arrhythmias, the device preferably identifies and a
Ben-Haim Shlomo
Darvish Nissim
Fenster Maier
Mika Yuval
Cowan Liebowitz & Latman P.C.
Deppert William H.
Impulse Dynamics N.V.
Jastrzab Jeffrey R.
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