Beyond the length and look of repolarization: Defining the non-QTc electrocardiographic profiles of patients with congenital long QT syndrome

Abstract

Little is known about the spectrum and prevalence of ECG features beyond the length and morphology of repolarization in patients with congenital long QT syndrome (LQTS). The purpose of this study was to characterize the full ECG phenotype of LQTS patients and evaluate differences by age and LQTS genotype. Retrospective review of 943 patients with LQTS (57% female; median age 25 years; interquartile range 9-34 years) was performed. Comprehensive analysis of their initial evaluation ECG was performed using definitions outlined in professional guidelines. Bradycardia was common (n = 320 [34%]), regardless of beta-blocker use. Left-axis deviation (n = 33 [3.5%]) and bundle branch block (n = 5 [0.5%]) were uncommon. T-wave inversion (TWI) involving leads V1 and V3 was more common in LQTS type 2 compared to LQTS type 1 or type 3 (odds ratio [OR] for V1: 2.67, 95% confidence interval [CI] 1.8-3.9; OR for V3: 1.76, 95% CI 1.2-2.6), whereas TWI in leads III and aVF was most common in LQTS type 3 (OR for III: 2.38, 95% CI 1.4-4.2; OR for aVF: 3.14, 95% CI 1.6-6.4). Notched T waves were most apparent at younger ages (48% in patients age 4-10 compared to 12% in patients age >40: P <.0001). Beyond the QT interval and bradycardia, ECG abnormalities are uncommon in LQTS patients, and patients almost never have concomitant bundle branch block. Notably, 19% of LQTS patients overall and 27% of LQTS type 2 patients exhibit anterior TWI that would satisfy a diagnostic criterion for arrhythmogenic right ventricular cardiomyopathy, thus creating the potential for diagnostic miscues.