Abstract 283: Repolarization Heterogeneity and Torsades De Pointes: A Case Control Study

Abstract

Introduction: Torsades de Pointes (TdP) is a potentially lethal ventricular tachydysrhythmia associated by definition with prolonged myocardial repolarization. However, prolonged myocardial repolarization is not specific for TdP. Our primary objective was to determine if heterogeneous myocardial repolarization manifested by corrected QT (QTc) and T wave variation is necessary and predictive of TdP. Methods: We performed an IRB approved case control study of TdP at a large urban hospital. We identified cases based on a MUSE ECG database search for tracings from 1/05 to 6/19 with QTc>500, QRS<120, and HR<60, and a subsequent natural language search of electronic health records for the terms: TdP, polymorphic ventricular tachycardia, sudden cardiac death, etc. Controls were drawn in a 2:1 ratio to cases from a similar pool of ECGs, and matching for sex, age, QTc, and heartrate. We abstracted historical, laboratory, ECG, and telemetry data using detailed written instructions and an electronic database. Groups were compared using unpaired and paired nonparametric and parametric statistics as appropriate. Results: We included 75 cases and 150 controls. We found no significant difference in measures of QTc or T wave repolarization heterogeneity, QTc prolonging medications, or serum electrolytes between the two groups. However, 35 cases had brief telemetry strips demonstrating TdP and a median of four beats prior to TdP onset. Ectopy was present in 25 (71%) strips prior to TdP. Heartrate in these cases was also 17 beats per minute (BPM) (95% CI 7 to 27) higher at an average 87 BPM just prior to TdP as compared to their index ECG. Conclusions: Repolarization heterogeneity is not greater in patients with QTc prolongation who suffer TdP. It doesn’t appear mechanistically necessary or predictive of TdP. Ventricular ectopy, possibly triggered from early after depolarizations, but not bradycardia, is common before TdP and may be usefully predictive.