Day to day variations in morphology and duration of fragmented ventricular potentials during the late post-myocardial infarction phase in conscious dogs

The relationship between the inducibility of ventricular tachyarrhythmias and the presence of fractionated epicardial ventricular electrograms ('late potentials') was studied daily between days 3 and 8 after experimental myocardial infarction in 15 conscious dogs. Before each programmed stimulation, epicardial infarct zone electrograms were recorded from implanted 'composite' electrodes during sinus rhythm. There was considerable daily variation in the morphology and duration of delayed ventricular activation, but no significant difference in duration of infarct zone electrograms was seen between studies resulting in ventricular fibrillation (108 +/- 62 ms, mean +/- SD), sustained ventricular tachycardia (87 +/- 18 ms), nonsustained (94 +/- 41 ms) or no tachycardia (78 +/- 5 ms). Although fractionated ventricular electrograms were commonly recorded early after infarction, their presence and duration could not predict the inducibility of malignant ventricular tachyarrhythmias. Similar limitations may apply in clinical practice to the use of surface signal averaging of ventricular late potentials in the early post-myocardial infarction period.