Recent progress in analysis of arrhythmias using electrocardiography

: Recently, various novel techniques have been used in clinic to analyze arrhythmias. These include vectorcardiography, body surface ECG mapping, signal-averaged ECG, intracardiac electrogram and monophasic action potentials, and 24-hour ECG recordings. We examined 24-hour ECG recordings in patients with frequent ventricular premature contractions (VPCs), to identify VPCs possibly due to delayed afterdepolarizations (DADs). We evaluated :1) the relationship between VPC frequency and heart rate (HR); 2) the time course of changes in VPC frequency following an abrupt and sustained increase in HR; and 3) the effects of oral diltiazem on VPCs. Patients could be divided into 2 groups according to whether VPCs increased with an increase in HRs (positive correlation or P group) or not (non-positive correlation or NP group). In the P group, changes in VPCs after an abrupt and sustained increase showed 2 types: 1) delayed-ascent type, in which VPCs increased as the duration of HR increase was prolonged; and 2) non-delayed-ascent type. Diltiazem suppressed almost only the VPCs of delayed-ascent type. The VPCs of delayed-ascent type had several important feature characteristic of DADs, suggesting these VPCs may be due to DADs.