Electrocardiographic Parameters Indicating Worse Evolution in Patients with Acquired Long QT Syndrome and Torsades de Pointes.

Abstract

Acquired long QT syndrome (a-LQTS) is associated with life-threatening ventricular arrhythmias, mainly torsades de pointes (TdP). ECG parameters predicting evolving into ventricular fibrillation (VF) are ill defined. To determine ECG parameters preceding and during TdP associated with higher risk of developing VF. We analyzed 151 episodes of TdP, recorded in 28 patients with a-LQTS (mean QTc 638 ms ± 57). All 28 patients had prolonged QT interval, (mean QTc 638 ms ± 57) ranging from 502 ms to 858 ms correcting by Bazett's formula. The mean TdP heart rate was 218 bpm ± 38 (mean cycle length of TdP 274 ± 47 ms). We classified TdPs episodes into "slower"-TdP (s-TdP) < 220 bpm (range from 145-220 bpm) observed in 81 (53.6%) episodes and "faster"-TdP (f-TdP) ≥ 220 bpm (ranged from 221-281 bpm) observed in 70 (46.4%) episodes. Among 151 episodes of TdP, 21 (13.9%) were unstable (converted into VF). Out of 81 episodes of "slower"-TdP only 2 (2.5%) episodes converted into VF. The mean coupling interval (CI) of the PVC initiating TdP was 510 ms ± 118, the pause-RR interval was 1147 ms ± 335, the prematurity index (PI) of PVC that initiated TdP was 0.45 ± 0.13. The mean cycle length variability of TdP (VRV-TdP) was 30.79 ms ± 19.7. U wave was observed in 86 episodes (56.9%), among that in 69 episodes, the U/T wave ratio was > 1. Macro T wave alternans was observed in 4 patients. The QT interval was not different in patients with VF(+) and VF(-) episodes, 633 ± 60 and 639 ± 57, respectively. Some electrocardiographic parameters can be helpful in determining the risk of TdP evolving into VF. The slower ventricular rate (< 220 bpm), the higher rate instability (VRV > 30 ms) and the short episodes < 20 beats could predict benign evolution.