Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-10-08
2002-10-08
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S005000
Reexamination Certificate
active
06463330
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for controlling the electrical activity of the heart. More particularly, the invention relates to a device and a method for the cessation and/or prevention of malignant cardiac arrhythmias.
BACKGROUND OF THE INVENTION
Sudden cardiac death is heralded by the abrupt loss of consciousness within a short period of time (usually not more than one hour) after the onset of acute symptoms. Estimates indicate nearly 400,000 sudden cardiac deaths annually for the USA only. Malignant cardiac arrhythmias such as Ventricular Tachycardia (VT) and Ventricular Fibrillation/Flutter (VF) are included in one category that is a major cause of sudden death usually associated with a diseased human heart. When VT/VF occurs, the patient may die within a few minutes without immediate intensive care. The conventional treatment which is normally given to the patient in the hospital is delivering a high energy electrical shock to the heart, usually from 200-400 Joules (J). The shock is applied between two electrodes (paddles) of an external defibrillator attached to the patient's chest. This shock resets the electrical activity of the heart, so as to enable a new natural initiation of normal electrical activity. However, these relatively high energy levels may cause heart tissue damage, especially in cases of multiple shocks, and in the long run may be dangerous, particularly in patients with a diseased heart. In addition, due to the severe pain caused by high energy impulses plus possible harm by severe contraction of the body musculature, high energy cardiac shocks are usually administered to unconscious or anesthetized patients.
The most effective method for appropriate management of patients who suffer from VT/VF is by employing an implantable cardiovertor defibrillator (ICD) device. This ICD applies electrical shocks directly to the heart when the device itself diagnoses VT/VF. These directly applied shocks are of much lower energy than those of the external defibrillator (normally ranging between 10 and 30 J), but, even this relatively low-energy application is very painful and may be harmful to the heart muscle in the long run.
Normal heart activity is controlled by impulses, which are generated at the sino-atrial node, and propagate from cell to cell through the special conduction system and myocardium, thereby causing an ordered contraction. Excitation in normal heart tissue is followed and terminated by refractoriness. This important feature of the heart provides it with electrical stability, so that abnormal excitation waves cannot propagate during the refractory period.
The exact mechanisms of malignant cardiac arrhythmias are not completely clear. In most cases it is assumed that they result from a “source” in the heart, around which a closed electrical circuit is generated, thereby forming a “reentry” path in the myocardium. There are two main approaches for management of malignant cardiac arrhythmia: pharmacological and non-pharmacological. The former generally can prevent and treat malignant cardiac arrhythmias, however its clinical effect for preventing sudden cardiac death is relatively low. In the non-pharmacological approach, malignant arrhythmias such as VT or VF may be treated by electrical shock (defibrillation/cardioversion) and can be prevented by ablation (annihilation) of part of the re-entry pathway or of the “source” of abnormal electrical activity.
All the methods described above have not yet provided complete satisfactory solutions to the appropriate overall management of malignant cardiac arrhythmias.
It is an object of the present invention to provide a method and a device for the management of malignant cardiac arrhythmia, which overcomes the drawbacks of the prior art.
It is another object of the present invention to provide a method and a device for the management of malignant arrhythmia, using very low energy impulses.
It is still another object of the present invention to provide a method and a device for the management of malignant arrhythmia without immediate or delayed negative effects on the patient's myocardium.
It is still another object of the present invention to provide a method and a device for the management of VT/VF, the use of which is not painful.
Other objects and advantages of the invention will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
While the device of the invention is designated herein as a “device for the cancellation of unwanted excitation waves”, it should be understood that the “unwanted excitation waves” are those causing cardiac tachyarrhythmias, and the use of the device to prevent or terminate these waves or other related pathological phenomena is included in the invention.
The device of this invention comprises the means for canceling unwanted excitation waves that propagate in an excitable tissue, by generating an excitation wave that spreads preferentially in a desirable direction. The excitation wave, also termed Device-Generated Excitation Wave (DGEW) may be directed opposite to that of the unwanted excitation wave and could cancel it or reduce it to such a magnitude that it ceases to propagate and decays. Said means for controlling the spread of the DGEW comprises two bipolar stimulating electrodes, which are adapted to be inserted into the excitable tissue at two different locations. Each stimulation electrode is fed by a power supply. Each stimulation electrode preferably comprises a pair of conducting needles, each of which comprises a relatively sharp tip at its distal end, and the proximal end of each such needle is connected to the contact of said power supply. When in use, each needle of the pair has an opposite polarity and they form a closed conducting current path through the underlying excitable tissue. The proximal end of each opposite-polarity needle is connected to a different contact of the corresponding power supply. When reference is made herein to a first and a second power supply, one for each pair of opposite-polarity stimulation electrodes, this should be understood to signify that the means for independently feeding power to each needle pair is provided, whether through two separate power sources or through a single power source with two separately controllable outputs. The device further comprises a first and second control circuitry, respectively, for generating the required amplitude and duration of the voltage applied between the respective needles. This forces a clamped current impulse to flow between the needles of each stimulation electrode. While reference is made to a first and second control circuitry, they can and generally are included in a single electronic circuit.
The first power supply, which drives the first stimulation electrode, is set to generate a first current stimulus, S
1
, with magnitude that is lower than the threshold level of the excitable tissue. Hereinafter, the term “threshold lever” is used to describe the current stimulus magnitude, at which the tissue becomes excited and the DGEW starts to propagate actively throughout the tissue. Stimuli below the threshold level cannot elicit an actively propagating wave along the tissue and decays over space and time. The second power supply, which drives the second stimulation electrode, is set to generate a second current stimulus, S
2
, with magnitude that is higher than the threshold level of the excitable tissue. The terms “first and second” current stimuli do not indicate timing, but indicate that the stimuli are delivered by the first and the second stimulating electrode, respectively.
The combination of S
1
and S
2
generates a DGEW, which spreads preferentially in one direction, that is controllable and can be made to be opposing to the unwanted wave. The delay between S
1
and S
2
is set by a timing circuitry to compensate for any change in the relative location between the two stimulation electrodes that may be desired.
Preferably, the distance between the two stimulating electrodes is adjusted to be approximately between 0.1
Ovsyshcher Eli
Rabinovitch Avinoam
Ben-Gurion University of the Negev
Layno Carl
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