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    • In contrast to the above similarities the prevalence of posi

    2019-06-06

    In tryptophan hydroxylase to the above similarities, the prevalence of positive late potentials [12,45–47] and the response to sodium channel blockade [48,49] differ between patients with BS and those with ERS. Roten et al. observed that the ER pattern in patients with ERS was attenuated by the administration of intravenous ajmaline. This novel finding, together with the low prevalence of late potentials, was proposed as evidence supporting the repolarization hypothesis of ERS. This is in contrast with the electrophysiologic findings (accentuation of J/ST wave changes, prevalent late potentials, and the presence of delayed potentials in the epicardium) in patients with BS, which supports the depolarization hypothesis. However, the pathogenetic mechanism in BS and ERS is not a simple dichotomy of depolarization and repolarization abnormalities. The early phase of ventricular repolarization is an overlap of late depolarization and early repolarization processes. In addition, these two processes affect each other. A change in the depolarization process causes a change in the repolarization process. This explains why a mutation or pharmacologic suppression of the sodium channel (and decrease in inward sodium current) is linked to an increased or accentuated phase 1 notch of repolarization process. Therefore, the response of BS patients to sodium channel antagonists may also be viewed as evidence supporting the repolarization hypothesis. Likewise, the response to ajmaline or attenuation of inferolateral ER pattern in patients with ERS may have been due to the conduction delay (and increased S wave amplitude) that masked or attenuated the J waves of ER pattern. The results and interpretation of the effects of sodium channel blocker in patients with BS or ERS need to be redefined.
    Phenotype overlap in patients with BS and ERS The typical type I BS ECG pattern shows spontaneous fluctuation and often manifests remote from VF events or in the absence of class IC antiarrhythmic drugs. By contrast, J waves and ER pattern in patients with ERS are stable over a long term and transiently manifest only during the peri-event period. Except for minor changes in amplitudes, the distribution of J wave or ST segment elevation in each ERS patient seldom changes significantly during follow-up. Although uncommon, a considerable overlap or shift in shape or distribution of the J waves (phenotype transition) may occur in patients with BS and ERS. For example, some patients with BS have been reported to demonstrate a background ER pattern [14]. In contrast, some patients with inferolateral ERS showed prominent J wave augmentation in the right precordial leads during peri-event periods (Fig. 7). This is an important clue that suggests ERS shares a key electrophysiologic mechanism with BS, providing further evidence to support the concept of “J wave syndrome”.
    Risk stratification The risk stratification of subjects who display a BS-type ECG pattern remains controversial. A history of syncope is the most important prognostic marker, but the predictive value of electrophysiologic study remains controversial. The prognostic importance of electrophysiologic study proposed in the early reports by Brugada et al. [50,51] has been challenged by subsequent investigations that failed to prove the efficacy of electrophysiology studies [52–55]. The annual cardiac event rate was reported as 7.7% in patients with aborted SCD, 1.9% in patients with syncope, and 0.5% in asymptomatic patients [54]. Because of this low risk and the uncertain predictive role of electrophysiologic study, a simpler approach is used, wherein the decision regarding ICD implantation is based largely on fatal ventricular arrhythmia or symptoms (syncope) [56]. An electrophysiologic study in asymptomatic subjects was designated a Class IIb indication. Other factors such as family history and SCN5A mutations were concluded to have little prognostic importance [54]. The risk stratification of patients with ERS is even more confusing and further studies are required. As mentioned in the demographics, the traditional definition of ER emphasizes the presence of ST segment elevation, and the subjects with ER with this traditional concept do not have adverse outcomes [17,18]. In contrast, patients with ER according to the new definition (the presence of the terminal QRS notch or slur, irrespective of the ST segment changes) [19–22], have prognostic implications. More specifically, individuals with J waves that were followed by ascending ST segment changes do not show an increased risk of arrhythmic death; however, those with J waves that were accompanied by horizontal/descending ST segment changes had an increased risk of arrhythmic death compared with those without the ER pattern [22]. Nevertheless, the hazard ratio of the arrhythmic death risk in the latter subgroup rises only slightly (hazard ratio, 1.43). Considering the low risk of arrhythmic death observed in the population study, even the high-risk marker of ER pattern (J wave and horizontal/descending ST) seems to reflect a modifying factor for specific arrhythmic risk in patients with acquired structural heart diseases, rather than an indicator of a primary arrhythmic syndrome, as discussed by the authors [22].