Distinguishing the genotype of pediatric long QT syndrome based on visual T-wave morphology

Background and Aim: In Japan, long QT syndrome (LQTS) is frequently diagnosed in junior high school students through school-based electrocardiographic screening, and its management varies with genotype. Although notched T-waves are characteristic of LQT2, they can also appear physiologically in children, making their diagnostic value in pediatric patients uncertain. Thus, this study evaluated their clinical significance. Materials and Methods and Results: We retrospectively reviewed 24 years of medical records from a single institution and analyzed clinical data and electrocardiograms obtained from junior high school-aged patients with genetically confirmed LQT1 or LQT2. T-wave morphology in the precordial leads was visually evaluated for notched, biphasic, or negative features, collectively defined as “broadly defined notched T-waves.” No significant differences were observed in age, sex, heart rate, or QT interval between the 20 patients with LQT1 and 10 patients with LQT2. Broadly defined notched T-waves were significantly more frequent in LQT2 than LQT1, especially in leads V3 (30% vs. 100%, P < 0.001) and V4 (5% vs. 50%, P = 0.009). In lead V3, broadly defined notched T-waves showed 100% sensitivity, 70% specificity, 63% positive predictive value, and 100% negative predictive value for distinguishing LQT2 from LQT1. In lead V4, these waves showed 50% sensitivity, 95% specificity, 83% positive predictive value, and 79% negative predictive value. Conclusions: In junior high school students with LQTS, notched T-waves in lead V4 are strongly associated with LQT2, whereas their absence in lead V3 suggests LQT1. These findings may aid in differentiating between LQT1 and LQT2 based on electrocardiographic morphology.