Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reissue Patent
1997-04-15
2001-12-25
Schaetzle, Kennedy (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S009000
Reissue Patent
active
RE037480
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable medical devices which deliver energy to cardiac tissue in an attempt to restore a normal sinus rhythm to a patient.
Tachycardia refers to any fast, abnormal rhythm of the heart which may be amenable to treatment by electrical discharges. One form of tachycardia is referred to as ventricular tachyarrhythmia (VTA). A common therapy for treating VTA is to implant a cardiac pacer/defibrillator in the patient, Cardiac pacers traditionally have been used to detect a slow heart rate and in response discharge electrical energy into the heart tissue at a faster pace which increases the heart rate. Pacing technology also can respond to the detection of arapid heart rate by producing rapid pacing which terminates the tachycardia and thereby causing the heart rate to return to normal. This present cardiac pacing technology is not specifically designed to reduce the occurrence of ventricular tachyarrhythmia, but rather to terminate the condition after it occurs.
However, rapid pacing techniques can accelerate and worsen the arrhythmias in some instances. As a consequence, cardiac pacers that treat rapid heart rates do so in conjunction with an implantable cardioverter defibrillator (ICD). The cardioverter defibrillator detects rapid ventricular tachyarrhythmias that do not respond to rapid pacing and employs cardioversion/defibrillation to terminate the arrhythmia.
Clinical studies have demonstrated that abrupt short to long changes in the ventricular cycle length often preceded and possibly precipitated ventricular tachyarrhythmia. The ventricular cycle length, i.e. the period between ventricular contractions, normally remains relatively constant and varies only gradually, even upon the commencement of strenuous exercise. However, occasionally a premature ventricular contraction occurs in the form of a spurious pulse from a muscle cell which disrupts the normal electrical pulse pattern in the heart. Because the heart tissue often does not recover from an early beat in time to conduct the next regular electrical pulse, the subsequent normal heartbeat does not occur. Thus, the heart undergoes very rapid beat followed by a significantly longer compensatory pause before a subsequent beat occurs. As a result, the heart is subjected to a very fast heart rate which quickly changes to a very slow rate. Such rapid rate change significantly intensifies dispersion of refractoriness in patients who already have other causes of increased dispersion of refractoriness, such as damaged ventricular myocardium from a myocardial infarction or cardiomyopathy. A premature ventricular contraction may facilitate tachyarrhythmia in these patients.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide an antitachycardia therapy device which detects a premature heartbeat followed by a resulting long pause and responds with corrective action to restore a normal heart rate by preventing the pause. This decreases dispersion and thereby lowers the incidence of VTA.
Another object is to electrically stimulate the heart to shorten the compensatory pause and thus reduce the severity of the short-to-long change in cardiac cycle length.
A further object of the present invention is to provide such functionality in an implantable cardiac pacer/defibrillator.
Yet another object is to enable the treatment initiation criteria to be programmable so that the operation of the antitachycardia therapy device may be configured for each particular patient.
These objects are satisfied by an apparatus that detects the occurrence of a very short cardiac cycle length followed by a long compensatory pause and responds by pacing the heart for one or several beats until a relatively constant rate is restored. The apparatus measures the cardiac cycle lengths and detects significantly premature heart beats by sensing abrupt changes heart cycles. When a heart beat fails to occur within a predefined time period after a significantly premature heart beat, cardiac pacing is initiated. For example, a series of electrical pulses are applied to produce contractions of the heart, until a normal heart beat occurs between the pulses.
In the preferred embodiment of this apparatus, a mechanism is provided for a physician to select a threshold value for the cardiac cycle length change, and the predefined time period before initiating the cardiac pacing technique.
This technique responds, to a ratio of two consecutive cycle lengths exceeding a defined magnitude as a precursor of ventricular tachyarrhythmia, by initiating pacing treatment. This is in contrast to conventional cardiac pacing which merely is responsive the heart rate slowing to below a set threshold level. Furthermore, conventional cardiac pacing responds by applying stimulating electrical pulses at a constant rate to produce heart beats at a constant cycle length and does not address preventing the onset of tachyarrhythmia.
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Duthler Reed A.
Medtronic Inc.
Patton Harold R.
Schaetzle Kennedy
Wolde-Michael Girma
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