Abstract 2193: Genetically-mediated Torsades De Pointes During Complete Heart Block
Background: Torsades de pointes (TdP) is a well known arrhythmic sequela in congenital and acquired long QT syndromes (LQTS). Less frequently, bradyarrhythmias are associated with QT prolongation and TdP. Although some observations have been made on the predictors of TdP in bradyarrhythmias, there is limited data on cellular mechanisms or genetic predisposition to bradycardia-induced TdP.
Methods: In a retrospective case-control study, we identified 11 patients who were referred with CHB and TdP. Comprehensive assessment was performed in these patients, including, history, examination, ECG parameters (baseline, in CHB and pre-TdP) and genetic testing of repolarization related ion channel genes. 33 control patients with CHB and no TdP were selected for comparison of ECG parameters. All patients received either a pacemaker or implantable cardioverter defibrillator, with outpatient follow-up.
Results: Four out of 11 patients with CHB and TdP had a genetic mutation identified involving ion channels responsible for cardiac repolarization (36%), involving hERG (n=3) and SCN5A (n=1). The key observations were that Tpeak to Tend interval was significantly longer in patients with a genetic abnormality at baseline, in CHB and pre-TdP (see Table 1⇓). Compared to controls, patients who had TdP complicating CHB had significantly longer QTc and Tpeak to Tend intervals in CHB.
Conclusion: TdP in the setting of CHB appears to identify patients who have an underlying genetic predisposition to reduced repolarization reserve. In particular, the terminal phase of repolarization (Tpeak to Tend) appears to be a marker for patients who have a cardiac ion channel abnormality. Given these findings, genetic testing should be considered in patients with TdP in the setting of CHB.