Abstract 3328: The Morphology of the T waves During Atrio-Ventricular Block Predicts the Occurrence of Bradyarrhythmia-Induced Torsade De Pointes
Background. Torsade de pointes is a life-threatening complication of bradyarrhythmias, particularly atrioventricular block (AV-block). Limited clinical data suggest that QT prolongation heralds torsade de pointes during AV-block.
Hypothesis. Since impaired potassium outward currents in patients with congenital long QT syndrome (LQTS) lead to specific T-wave abnormalities, and since animal studies show that the QT prolongation during AV-block is due to down-regulation of potassium channels (also leading to impaired potassium currents), we speculated that T-wave abnormalities, similar to those seen in the congenital LQTS, would predict the occurrence of torsade de pointes during acquired AV-block.
Methods. We conducted a case-controlled study of 30 cases with AV-block complicated by torsade de pointes and 114 cases with uncomplicated AV-block. We compared the duration of the QT and QTc intervals as well as the T wave morphology during AV-block between patients with and without torsade de pointes. T-wave changes during AV-block were defined as “LQT1-like” when they resembled the broad T waves typically seen in the LQT1-type of the congenital LQTS. Similarly, “LQT2-like” changes included double or “notched T waves” and LQT3-like changes included small T waves of very late onset (as typically seen in the LQT2 and LQT3 types of congenital LQTS, respectively). T2>T1 denotes that the second component of a double T wave was taller than the first one.
Results: By multivariate logistic regression analysis, the QT interval, QTc interval, and the presence of “LQT2-like morphology” were independent and additive predictors of torsade de pointes. Having a QT of more than 590 msec and a LQT2-like morphology almost surely predicted the occurrence of torsade de pointes (positive predictive value = 93%).
Conclusions: We conclude that T wave changes, reminiscent of those seen in the LQT2-type of congenital LQTS, are predictive of torsade de pointes during acquired AV-block.