Functional changes of ventricular late potentials by provocation with increase of heart rate. Evaluation during atrial pacing

BACKGROUND: Standard methods fail to reveal late potentials in 20 to 30% of patients with ventricular arrhythmias after myocardial infarction. However, these patients may develop transient delayed ventricular activation during increases in heart rate. METHODS AND RESULTS: Atrial pacing was performed, at the rates of 100 min-1 and 120 min-1, in 50 patients after myocardial infarction. Twenty-six patients had a history of documented, sustained ventricular tachycardia, 12 had a history of ventricular fibrillation and 12 no history of ventricular arrhythmias. The low-noise surface electrocardiogram was analysed before and during atrial pacing in the time and frequency domains. Fifteen of 26 patients with ventricular tachycardia, four of 12 with ventricular fibrillation and three of 12 without ventricular arrhythmias experienced late potentials during sinus rhythm. Atrial pacing led to a shift of 26 +/- 15 ms of preexistent late potentials into the ST segment, this being greater in patients with anterior infarctions and to an increase in magnitude in patients with inferior infarctions. In patients without late potentials during sinus rhythm, atrial pacing provoked late potentials in eight of 11 patients with ventricular tachycardia, in four of eight patients with ventricular fibrillation and in one of nine patients without ventricular arrhythmias. Low amplitude signals (LAS) were increased in patients after inferior and filtered QRS in patients after anterior infarction. In 10 patients without cardiac disease no late potentials were detectable in the time and frequency domain either at rest or during increased heart rate. CONCLUSIONS: Increase in heart rate may unmask late potentials in patients prone to malignant ventricular arrhythmias. Therefore, functional late potential analysis with non-invasive clinical stress tests, i.e. exercise tests, should be performed only with an adequate rate response. This might identify patients at risk of malignant ventricular arrhythmias otherwise not identified with conventional late potential analysis.