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

Background: 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).

Objective: The purpose of this study was to characterize the full ECG phenotype of LQTS patients and evaluate differences by age and LQTS genotype.

Methods: 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.

Results: 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).

Conclusion: 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.