Bradycardia-induced abnormal QT prolongation in patients with complete atrioventricular block with torsades de pointes

Abstract

Fourteen patients with complete atrioventricular block with or without torsades de pointes (TdP) were included in this study. They were divided into 2 groups, 6 patients with TdP (TdP[+] group) and 8 patients without TdP (TdP[−] group). The patients were evaluated at 2 different periods, before (acute period) and after (chronic period) pace-maker implantation. In the acute period, the QRS and heart rate during the escape rhythm were not significantly different between the 2 groups; however, the QT and QTc intervals were significantly longer in the TdP(+) group than in the TdP(−) group: 753 ± 57.5 vs 635 ± 78.4 ms (p < 0.01) and 585 ± 44.8 vs 476 ± 58.3 ms (p < 0.01). In the chronic period (>2 months after pacemaker implantation), we changed the pacemaker rate from 90 or 100 beats/min to 50 beats/min and examined the QT interval changes in relation to the heart rate. The QT interval in the TdP(+) group was significantly prolonged compared with the TdP(−) group when the pacing rate was decreased ≤ 60 beats/min: 551 ± 40 vs 503 ± 36 ms at 60 beats/min (p < 0.05), and 700 ± 46 vs 529 ± 43 ms at 50 beats/min (p < 0.001). Patients with complete atrioventricular block with TdP had a brady-cardia-sensitive repolarization abnormality and this characteristic remained after pacemaker implantation. The critical heart rate that induced abnormal QT prolongation in the TdP(+) group was ≤ 60 beats/min.