Mode of onset of polymorphic ventricular tachycardia in acute myocardial infarction

BACKGROUND: Polymorphic ventricular tachycardia (PVT) can occur during acute myocardial infarction (MI). In the past, studies investigated the initiation pattern of ventricular tachycardias in different patient populations; however, the mode of onset of PVT in acute MI patients has not been investigated previously. OBJECTIVE: To retrospectively investigate the electrophysiological features of PVT with different initiation patterns in acute MI patients to assess whether there is a relationship of the initiation patterns of PVT with clinical and electrophysiological characteristics. METHODS: Sixty-two rhythm strips defined as PVT from 53 patients (mean [+/- SD] age 63+/-8 years) with acute ST elevation MI were analyzed. All patients were monitored while they were hospitalized in the coronary care unit, and the electrocardiogram strips were obtained from continuous monitoring. PVT was defined as sudden-onset tachycardia if it was not preceded by ventricular ectopic beats. PVT that was preceded by single or multiple ectopic beats was defined as nonsudden-onset tachycardia. RESULTS: Nonsudden-onset episodes were more common than sudden-onset episodes (40 episodes [64.5%] versus 22 episodes [35.5%]). In the nonsudden-onset group, 25 episodes (62.5%) were initiated after a single ectopic beat, while 15 episodes (37.5%) were initiated after multiple complexes. The mean (+/- SD) left ventricular ejection fraction of patients with nonsudden-onset PVT was decreased (53+/-6% versus 65+/-7%, P<0.01). Nonsudden-onset tachycardias had lower coupling intervals than sudden-onset tachycardias. Similarly, the PVT cycle length was shorter in the presence of nonsudden-onset initiation. When nonsudden-onset PVT episodes were further subclassified based on the morphology of the first beat of tachycardia, 26 PVTs (65%) had a first beat of tachycardia similar to the subsequent PVT beats and 14 (35%) did not. CONCLUSIONS: These results demonstrate that PVT is often preceded by ventricular ectopy in acute MI patients. Nonsudden-onset PVT is usually characterized by a lower coupling interval, shorter PVT cycle length and an associated lower ejection fraction.