Cardiac rhythm management devices known as implantable cardioverter/defibrillators (ICDs) are designed to treat ventricular tachyarrhythmias by delivering an electrical shock pulse to the heart. Cardioversion and/or defibrillation can be used to terminate most tachyarrhythmias, including VT and VF. The electric shock terminates the tachyarrhythmia by depolarizing all of the myocardium simultaneously and rendering it refractory.
The present invention relates to an algorithm that can be implemented in a cardiac rhythm management device for tachycardia detection and for discriminating between a ventricular tachycardia and a supraventricular tachycardia when both the atrial and ventricular rates are elevated and within defined tachycardia ranges. The device detects tachycardias by detecting atrial and ventricular senses corresponding to atrial and ventricular depolarizations, respectively, and measuring the cycle length between consecutive senses in each chamber. An AA interval corresponding to a cycle length between consecutive atrial senses, and a VV interval corresponding to a cycle length between consecutive ventricular senses, are both computed, preferably as a median or other statistic of a number of individual cycle lengths measured during a data collection time window. Ventricular fibrillation (VF) is then detected when the VV interval is below a VF threshold. If the VV interval is within a tachycardia range defined as above the VF threshold but below a VT threshold, and the AA interval is within normal limits, a ventricular tachycardia (VT) is detected. If the AA interval is within a tachycardia range defined as below an SVT threshold, and the VV interval is within normal limits, a supraventricular tachycardia (SVT) is detected. A dual tachycardia is detected if the VV and AA intervals are both within their respective tachycardia ranges and differ by more than a specified dual tachycardia limit value. A dual tachycardia refers to condition in which both VT and SVT are present simultaneously. A dual tachycardia is presumed when the atrial and ventricular rates are so different from one another that the atria and ventricles can be assumed to be independently driven. Since VT is the more serious condition, a dual tachycardia can be regarded as a VT for treatment purposes.