Electrocardiographic predictors of bradycardia-induced torsades de pointes in patients with acquired atrioventricular block

Background Predictors of torsades de pointes (TdP) in bradyarrhythmia-induced acquired long QT syndrome are not well defined. Objective The purpose of this study was to search for electrocardiographic (ECG) TdP predictors in patients with acquired atrioventricular block (AVB) and QT prolongation. Methods We analyzed 12-lead ECGs from 20 patients (15 females, age 65.9 ± 15.6 years) with TdP episodes from among 898 AVB patients (2.2%) in 3 tertiary hospitals. The ECG repolarization parameters in TdP patients were compared with those of 80 age- and sex-matched control AVB patients with no TdP episodes. Results TdP was initiated by premature ventricular complexes with a long-short sequence of activation. The average cycle length of the long sequence was 1289.9 ± 228.9 ms and was 2.3 ± 0.6 times longer than the cycle length of the short sequence. TdP patients had a significantly longer mean QT interval (716.4 ± 98.9 ms vs 523.2 ± 91.3 ms, P =.001), mean T peak to end interval (334.2 ± 59.1 ms vs 144.0 ± 73.7 ms, P =.001) and a higher T peak to end interval/QT ratio (0.49 ± 0.09 vs 0.27 ± 0.11, P =.001) compared with non-TdP controls. TdP patients showed a higher prevalence of notched T waves in which T₂ was at least 3 mm taller than T₁ (45.0% vs 1.3%, P =.001), triphasic T waves (30.0% vs 1.3%, P =.001), reversed asymmetry (20.0% vs 0%, P =.001), and T-wave alternans (35.0% vs 0%, P =.001). An algorithm combining these morphologic parameters was able to differentiate TdP patients from non-TdP patients with high sensitivity (85.0%) and specificity (97.5%). Conclusion An algorithm combining specific T-wave morphologies was useful for identifying patients with AVB who are at risk for developing TdP.