Area-of-difference methods for detection of ventricular tachycardia using morphology

To improve the detection of pathological tachycardias by implantable antitachycardia devices, techniques based on changes in intraventricular electrograms during sinus rhythm or atrial fibrillation and ventricular tachycardia (VT) are proposed. The area of difference (AD), among the simplest of these proposed methods, sums the absolute difference between the stored template and each electrogram under analysis. To determine whether amplitude and/or baseline fluctuations might affect the results, four area methods were compared. The normalized area of difference (NAD) is independent of amplitude changes, the mean area of difference (MAD) is independent of baseline changes, the normalized mean area of difference (NMAD) is independent of both amplitude and baseline changes, and AD is dependent on both amplitude and baseline changes. The results indicate that the results of the four algorithms are very similar, but algorithms independent of baseline changes are more sensitive to template misalignment