Prevalence of early repolarization in congenital long QT syndrome. A combination of early and delayed repolarization

Abstract

Introduction: Early Repolarization (ER) in Brugada or short QT syndrome is common and has been associated to a less favourable outcome. Even if apparently paradoxical, ER can also be seen in Long QT (LQT) but prevalence and correlations to other variables are unknown. Methods: 12 leads ECG of 41 LQT patients (21 men, 37±22 yo) were reviewed and compared to 97 matched controls (54 men, 39±24 yo) LQT patients were selected by a positive genetic testing (n=33) or by showing abnormal T wave and long QT interval spontaneously or during epinephrin infusion in patients without discovered genetic mutation (n=8). ER was defined by ≥ 1 mm J point elevation in the inferior or lateral leads with a notch or slurring pattern. Presence of ER was correlated to the clinical and ECG characteristics and to the results of genetic analysis. Results: QT was 406±52 msec in LQT patients and 354±42 in controls (p≤0.0001) (QTc 433±34 versus 386±26 msec, p≤0.0001). Two LQT patients presented with ressuscitated sudden death and 4 with syncope at the time of diagnosis. 14/41 LQT patients (34%) had ER compared to 14/97 (14%) controls (p=0.008). Heart rate was not different between patients and controls (64±10bpm versus 73±20bpm, p=0.14). ER was more frequent in men (12/21, 57%) compared to women (2/20, 10%) (p=0.004) but was not correlated to age (41±22 yo with ER versus 35±22bpm, p=0.4). ER was not correlated to symptoms or cardiac events (no ER in the 2 patients with SD and in 2/4 patients with syncope versus 12/35 in asymptomatic LQT patients, p=ns). There was a trend toward longer QT in patients with ER (427±40 versus 396±54 msec in V2, p=0.09) but there was no correlations between ER and corrected QT intervals. This can be explained by the lower heart rate in patients with ER (63±10 versus 75±18bpm, p=0.03). ER was not more often seen in patients with or without mutations (11/33 versus 3/8, p=0.8), but there was more frequent ER in case of HeRG mutations (9/17) than in case of KCNQ1 or KCNJ2 mutations (2/13 and 0/3) (p=0.04) Conclusion: ER is very common in LQT patients and is related to a male gender, to a longer QT duration and to a slower heart rate but not to age or to the corrected QT duration. ER does not seem to be correlated to cardiac events in this series but may be linked to HeRG mutations. Further studies are needed for demonstrating additional mutations/variants or the existence of an early transient voltage gradient due to altered kinetics in muted potassium channels with loss of function especially for HeRG mutations.