Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Utility Patent
1999-04-23
2001-01-02
Evanisko, George R. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C600S515000
Utility Patent
active
06169923
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to an implantable cardioverter-defibrillator which applies arrhythmia-terminating electrical energy to a heart when an arrhythmic episode is detected. The present invention is more particularly directed to such a device, wherein arrhythmic episode detection criteria are adjusted in response to arrhythmic episode detection confirmation results.
BACKGROUND OF THE INVENTION
Implantable cardioverters-defibrillators, such as implantable ventricular defibrillators, are well known in the art. Such devices include an arrhythmia detector which detects an arrhythmic episode of the heart and an output circuit or generator which applies electrical energy to a heart when an arrhythmic episode is detected to terminate the detected arrhythmia.
The performance of an arrhythmia detector is generally measured by its sensitivity and specificity. Sensitivity is the measure of how well a detector detects all of the arrhythmic episodes. For example, a detector that has a sensitivity of 100% detects all arrhythmic episodes of the type intended to be detected which occur. Specificity, on the other hand, is the measure of how well the detector is able to distinguish or discriminate the arrhythmia intended to be detected from other arrhythmias. For example, an arrhythmia detector which has a specificity of 100% detects only the arrhythmia intended to be detected, and no others.
There are many different types of cardiac arrhythmias. Among these are, for example, ventricular fibrillation, ventricular tachycardia, atrial fibrillation, and atrial tachycardia or flutter. Hence, a ventricular fibrillation detector which is has a sensitivity of 100% and a specificity of 100% is able to detect all ventricular fibrillations episodes that occur(100% sensitive) while at the same time not mistaking any other form of arrhythmic episode for ventricular fibrillation (100% specific).
Although modern implantable cardiovertersdefibrillators employ arrhythmia detectors which have very high sensitivities and specificities, no arrhythmia detector has both a sensitivity and specificity of 100%. Ventricular fibrillation is an immediately life threatening arrhythmia. Hence, all ventricular fibrillation episodes must be detected and, when detected, terminated quickly. As a result, a ventricular fibrillation detector must be very sensitive. In fact, to assure such sensitivity, it is desirable to tolerate some arrhythmic episodes, other than ventricular fibrillation episodes, to be detected as ventricular fibrillation. These are known as false positives.
In order to reduce unneeded, attempted arrhythmic episode terminations, it is well known to provide confirmation of detections. When a ventricular fibrillation episode is initially detected, a storage capacitor which applies the arrhythmia terminating electrical energy to the heart begins charging. Either during or immediately after charging the initial ventricular fibrillation episode detection is confirmed. If confirmation is successful, the arrhythmia terminating electrical energy is immediately applied to the heart. However, if confirmation of the initial ventricular fibrillation episode detection is unsuccessful, the energy delivery is aborted. Such unsuccessful confirmation can, for example, be the result of a false positive in the initial detection or the heart spontaneously returning to a normal rhythm in the short time period between initial detection and unsuccessful confirmation.
The detection parameters or criteria used in the initial detection of ventricular fibrillation episodes represent a difficult tradeoff for the physician. If the number of heartbeats to be analyzed is set too high, there could be a significant delay in the detection of the ventricular fibrillation episodes. If the number of heartbeats to be analyzed is set too low, the confidence that a rhythm detected as ventricular fibrillation truly being ventricular fibrillation is reduced. If the criteria applied to the analyzed beats are set too high, the detection will be overly specific and relatively insensitive resulting in the potential that a ventricular fibrillation episode will go undetected. Lastly, if the criteria applied to the analyzed beats are too low, the opposite problem can occur and the detection will be overly sensitive and relatively unspecific resulting in inappropriate shocks being delivered to the heart.
The present invention addresses these issues. More particularly, as will be seen hereinafter, the confirmation results of the confirmation detection are utilized for the automatic adjustment or regulation of the initial arrhythmia detection criteria to assure maximum sensitivity with appropriate specificity in the initial arrhythmic episode detection parameters or criteria.
SUMMARY OF THE INVENTION
The invention provides an arrhythmia detection system that provides automatic detection criteria adjustment for use in an implantable cardioverter-defibrillator that applies arrhythmia terminating electrical energy to a heart responsive to detection of an arrhythmic episode of the heart. A first detector detects arrhythmic episodes of the heart in accordance with detection criteria. A second detector confirms the detection of each arrhythmic episode by the first detector and a detection criteria regulator adjusts the detection criteria of the first detector responsive to the second detector.
In accordance with one aspect of the present invention, the detection criteria regulator adjusts sensitivity and specificity detection criteria of the first detector. The second, or confirmation detector provides one of successful and unsuccessful confirmation results for each arrhythmic episode detected by the first detector. In accordance with a further aspect of the present invention, the detection system further includes a counter that counts consecutive confirmation results provided by the second detector. The detection criteria regulator adjusts the detection criteria of the first detector in response to the counter counting either at least two consecutive successful confirmation results or two consecutive unsuccessful confirmation results.
In accordance with a further aspect of the present invention the arrhythmia detection system includes a processor, coupled to a ventricular activation detector, that times successive time spans between successive detected ventricular activations and executes an X out of Y routine wherein Y is the total number of successive time spans to be timed for a ventricular arrhythmic episode to be detected and X is the number of time spans shorter than a predetermined time span of the successive number of total time spans required for a ventricular arrhythmic episode to be detected. The detection criteria regulator adjusts the values of X and y.
In accordance with a further aspect of the present invention, the detection system includes a ventricular activation rate variability factor calculator that determines the ventricular activation rate variability. When the ventricular activation rate variability exceeds a given factor, the detection criteria regulator causes the number of heartbeats to be analyzed to be increased or to remain constant.
In accordance with a still further aspect of the present invention, an abort stage causes the application of arrhythmia terminating electrical energy to be inhibited if an arrhythmic episode detection confirmation is unsuccessful. Moreover, the storage capacitor that stores the arrhythmia terminating electrical energy may be reformed when such reforming is required and if a confirmation of an arrhythmic episode detection is unsuccessful.
The invention further provides in an implantable cardioverter-defibrillator that applies arrhythmia detecting electrical energy to a heart responsive to detection of an arrhythmic episode of the heart, an arrhythmia detection system that provides automatic detection criteria adjustment. The system includes first detecting means for detecting arrhythmic episodes of the heart in accordance with detection criteria, second detecting
Evanisko George R.
Pacesetter Inc.
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