Approximate entropy as a measure of morphologic variability for ventricular tachycardia and fibrillation

Ventricular fibrillation and ventricular tachycardia have very distinct characteristics including heart rate and morphologic differences. In addition, with ventricular fibrillation there are varying levels of organization of the signal. Despite obvious visual distinctions, no measure has been able to accurately quantify these differences or the level of variability. Approximate entropy is a nonlinear measure of complexity used in other physiologic applications. The purpose of this work was to evaluate this measure as a descriptor and/or classifier of ventricular tacharrhythmias for potential use in medical devices and for basic mechanistic research. From these results, approximate entropy was able to quantify the regularity of VT and VF, where VF had much higher entropy values due to its variability. However, no single threshold was able to completely separate VT and VF due to the patient variability