Assessment of mechanisms of ventricular arrhythmias from the surface ECG in 118 patients.

Mechanisms of ventricular arrhythmias were assessed by the application of ECG criteria derived from experimental electrophysiology. These interval criteria describe for ideal and modulated parasystole, resetable spontaneous automaticity, early and delayed afterdepolarizations and reentry, how QRS complexes of ectopic ventricular origin relate to those of supraventricular origin. Ventricular arrhythmias were studied in: (a) long-term, 1-lead ECG recordings of 85 patients with uncomplicated and untreated acute myocardial infarction (AMI) (group 1); (b) one-hour, 4-lead ECG recordings of 23 comparable patients with AMI (group 2), and (c) one-hour, 4-lead ECG recordings of 10 patients with chronic ventricular arrhythmias (group 3). All QRS complexes of ectopic ventricular origin having identical morphology (V type) were assumed to be the manifestation of a single site in the ventricle. The supraventricular rhythm in groups 2 and 3 was varied by programmed atrial stimulation to increase the range of intervals and patterns of the V types in the ECG. Positive evidence for a particular mechanism was obtained by applying tested criteria in 38% of 263 V types in group 1 (mainly reentry, but also early and delayed afterdepolarizations). In group 2, there was positive evidence in 67% of 84 V types (mainly reentry, but also early and delayed afterdepolarizations) and also in 67% of 18 V types in group 3, (mainly reentry). The application of these ECG criteria to ventricular arrhythmias identifies mechanisms in a satisfactory proportion. The yield can be increased by artificial variation of the heart rate.