Figure 1.

Schematic representation of the heart and a recording of cardiac electrical activity or an electrocardiogram (ECG) during an event of sudden cardiac death due to a transition from normal rhythm (sinus rhythm) to an episode of ventricular tachycardia, which was initiated by a premature ventricular complex or premature ventricular complex (PVC) (indicated by *). The heart rate variability (HRV) indices are based on the interval between consecutive normal beats (NN interval). By contrast, the heartprint indices include the coupling interval (CI) and the number of sinus intervening beats (NIB) between two consecutive PVCs.