br Discussion Early repolarization is a common ECG character
Discussion Early repolarization is a common ECG characteristic. Its reported prevalence is 6–25% of the general population, and is particularly common in athletes [2,3,11,12]. It is now recognized that a small fraction of people with early repolarization on their ECGs develop lethal tachyarrhythmias. Thus, idiopathic VF patients with early repolarization are rarely encountered in clinical practice. Actually, in the J-PREVENT registry, only 29 patients with early repolarization syndrome (8 patients were not included in the present study, because they did not undergo electrophysiological study) were enrolled from 10 centers over several years. Currently, primary ICD therapy is therefore not indicated for subjects with early repolarization pattern. However, if a risk THZ2 scheme could be developed to identify those at risk with high specificity, those patients would be candidates for ICD implantation. To date, amplitude of the J-point and specific ST-segment morphology have been reported to be associated with higher risk in subjects with early repolarization pattern [13,14]. Less is known about the utility of conducting electrophysiological study in early repolarization syndrome, as compared to Brugada syndrome. In the present study, 20 of the 21 patients with early repolarization syndrome had as their first cardiac event, aborted sudden cardiac death or VT/VF. These patients are obviously at high risk compared to subjects without prior cardiac events. Yet, we found that ventricular arrhythmias were inducible in only 43% (9 of 21) of the patients. Furthermore, inducibility was not predictive of recurrence of arrhythmia. Our data suggest limited predictive value of electrophysiological study for early repolarization syndrome patients. Further study is required to evaluate to what extent the current results can be extrapolated to subjects without prior cardiac events. The following are some of the clinical similarities between early repolarization syndrome and Brugada syndrome: the dynamic nature of the J wave, such as its pause or bradycardia dependent augmentation [15–18], suppression of J wave or VF storm by isoproterenol [19,20], and predominant occurrence of VF at nighttime . On the other hand, there are also differences between these two syndromes. Firstly, early repolarization syndrome and Brugada syndrome are different in terms of location of ECG leads of the J-point elevation. This is considered to represent differences in the anatomical location of the repolarization abnormality. Roten et al. reported stroma the effects of ajmaline on the J wave differed . The presence of late potentials also differs. In early repolarization syndrome, late potentials are absent in most patients, while late potentials are present in 60–92% of Brugada syndrome patients [23–25]. From these facts, depolarization abnormality is less likely to contribute to arrhythmogenicity in early repolarization syndrome, compared to Brugada syndrome. This is consistent with our finding of a lower inducibility rate in early repolarization syndrome. Previous studies have suggested that not only a repolarization abnormality but also a depolarization abnormality underlies the pathophysiology of Brugada syndrome [26,27]. Ventricular arrhythmias were not inducible in the present study in more than half of the patients with early repolarization syndrome. A more aggressive ventricular stimulation protocol may have increased rate of inducibility. It is also possible that the arrhythmia substrate varies temporally in early repolarization syndrome. In both early repolarization syndrome and Brugada syndrome, arrhythmic events occur more frequently in the nighttime . However, weekly distribution of arrhythmic events is different between these two. We reported that early repolarization syndrome patients and Brugada syndrome patients had arrhythmic events more frequently on weekends and weekdays, respectively . Thus, electrophysiological study performed at nighttime on weekend may have increased inducibility in early repolarization syndrome. Factors associated with the circadian rhythm such as autonomic tone and humoral factors potentially play a role in the arrhythmia substrate of the early repolarization syndrome and Brugada syndrome .