From Complete Heart Block to Torsades de Pointes

BACKGROUND: Complete atrioventricular block is a recognized cause of acquired QT prolongation and Torsades de Pointes. CASE SUMMARY: An 80-year-old woman with no known prior cardiac history presented to the emergency department with acute confusion and altered mental status. There was no reported history of syncope, palpitations or structural heart disease. Baseline electrocardiography demonstrated complete atrioventricular block with a stable junctional escape rhythm and marked corrected QT prolongation (QTc 545 ms). Continuous electrocardiography monitoring revealed sudden-onset polymorphic ventricular tachycardia consistent with Torsades de Pointes. TAKE-HOME MESSAGES: Cardiac memory-induced repolarization abnormalities can trigger Torsades de Pointes in complete complete atrioventricular block despite stable RR intervals. Sudden changes in QRS morphology and axis due to alteration of the escape rhythm during atrioventricular block with persistent T-wave orientation represent an important electrocardiographic warning sign (cardiac memory) because they may lead to further prolongation of the QTc interval and the onset of Torsades de Pointes.