Giant T–U Waves Precede Torsades de Pointes in Long QT Syndrome

Abstract

This study sought to identify electrocardiographic (ECG) criteria that are associated with initiation of torsades de pointes (TdP) in patients with acquired (a-) and congenital (c-) long QT syndrome (LQTS). Electrocardiographic criteria used as risk predictors for TdP commonly rely on a prolonged QT interval but rarely consider abnormal T-U waves. We analyzed ECG recordings with TdP from 35 LQTS patients (15 c-LQTS and 20 a-LQTS) and compared them with premature ventricular complexes (PVCs) from 40 patients with normal QT intervals and with PVCs in 24 of the 35 LQTS patients not related to TdP. Abnormal T-U waves (6.2 +/- 0.9 mm) directly preceded TdP in 34 of 35 LQTS patients and were larger than T-wave amplitude (2.8 +/- 0.2 mm) in control patients and larger than the largest T-U-wave in LQTS without TdP (4.7 +/- 0.8 mm). The TdP-initiating beat emerged from a T-U-wave in 27 of 35 LQTS patients and in none of 40 control patients. The QRS duration of the first TdP beat (175 +/- 12 ms) was longer than in control PVCs (145 +/- 4 ms) and in PVCs in LQTS patients not related to TdP (138 +/- 22 ms). The QRS angle was less steep before TdP than in other PVCs (all p < 0.05). Abnormal, giant T-U waves separate TdP initiation in LQTS patients from PVCs in other heart disease and from other PVCs in LQTS patients. These ECG analyses suggest that early afterdepolarizations initiate TdP and, if present, may help to identify an imminent risk for TdP.