Significance of R-on-T phenomenon in early ventricular tachyarrhythmia susceptibility after acute myocardial infarction in the thrombolytic era

We investigated the clinical significance and mechanism of the R-on-T pheno menon in the current thrombolytic era as potential precipitant of R-on-T-in duced early ventricular tachyarrhythmias in patients with a thrombolysed ac ute myocardial infarction, We also examined the role of QT dispersion on ve ntricular vulnerability and its association with R-on-T-initiated ventricul ar tachyarrhythmias. A total of 93 patients underwent 24-hour Holter monito ring starting at hospital admission before thrombolysis. Patients were clas sified into 2 groups: those with (n = 76) and those without (n = 17) reperf usion according to electrocardiographic criteria. All R-on-T ventricular pr emature complexes (VPCs) and R-on-T-initiated arrhythmic events (ventricula r tachycardia [VT], ventricular fibrillation) were counted to estimate arrh ythmia density and severity in 2 time periods during and after completion o f thrombolysis. Measurements of QT and QTc intervals and dispersion paramet ers were obtained on the 12-lead electrocardiogram before thrombolysis and at 24 hours in patients with and with-out R-on-T VTs. Overall, R-on-T VPCs were rarely observed (1.8% of total VPCs over 24 hours), occurring more fre quently during than after thrombolysis (at a rate of 8 vs 0.6 VPCs/hour, p = NS) and at a higher rate during thrombolysis in nonreperfused than in per fused patients (15 vs 8/hour, p = NS). Three VF episodes were observed in 1 reperfused patient, and all were R-on-T initiated. Episodes of nonsustaine d R-on-T VTs (3.3% of total VTs over 24 hours) appeared more frequent durin g than after thrombolysis (at a rate of 0.8 vs 0.05 VPCs/hour, p = NS), and compared with non-R-on-T VTs they were significantly faster (374 +/- 56 ms vs 411 +/- 69 ms; p < 0.05), with a trend toward longer duration. Our find ings indicate that R-on-T VPCs and R-on-T VTs are early rare features in ac ute myocardial infarction, and do not serve as triggers of severe ventricul ar tachyarrhythmia. The study of ventricular repolarization did not elicit an identifiable risk factor of R-on-T VT susceptibility. (C)2000 by Excerpt a Medica, Inc.