Detection of cardiac tachyarrhythmias in implantable devices.

Implantable devices such as pacemakers and implantable cardioverter/defibrillators (ICDs) use algorithms to sense cardiac depolarizations and to detect tachyarrhythmias by analysis of timing and morphology of sensed events. The purpose of tachyarrhythmia detection in these devices is to guide electrical therapies delivered by the pacemaker or ICD and/or to provide clinical diagnostics for medical management of patients. Unlike electrocardiographic analysis methods that rely on postanalysis of recorded signals using desktop computers, implantable devices must make detection decisions on a beat-by-beat basis with algorithms that can be implemented in battery-powered devices with longevities of up to several years. Cardiac sensing in implantable devices is achieved using amplifiers, bandpass filters, and adaptive thresholds to avoid oversensing of cardiac and noncardiac activity, while avoiding undersensing of low-amplitude cardiac activations during fibrillation. The tachyarrhythmia detection algorithms are formed by combining different building blocks of rhythm information extracted from timing of cardiac activations and from electrogram morphology information. Tachyarrhythmia detection algorithms in ICDs were originally designed to achieve high sensitivity for detection of life-threatening tachyarrhythmias such as ventricular tachycardia and ventricular fibrillation. Much of the progress in ICD detection algorithms in the past 15 years has been in the development of supraventricular tachycardia discrimination algorithms to reduce the number of inappropriate therapies delivered by ICDs. This article provides an overview of current tachyarrhythmia detection approaches, describe challenges facing tachyarrhythmia detection algorithm performance in ICD patients with primary prevention indications, and presents future directions in cardiac tachyarrhythmia detection for implantable devices.