Dynamics of J-point amplitude in early repolarization syndrome patients resuscitated from out-of-hospital ventricular fibrillation: Beware of "concealed" early repolarization syndrome

Background We previously reported a case of early repolarization syndrome (ERS) who exhibited ER pattern appeared only at the day of ventricular fibrillation (VF) storm. Purpose The aim of this study was to investigate the dynamics of J-point amplitude in ERS patients resuscitated from out-of-hospital VF. Methods This study included 10 consecutive ERS patients (median age, 47 years; 9 men) and 3 consecutive idiopathic VF patients (median age, 56 years; 3 men) resuscitated from out-of-hospital VF. The J-point amplitude was measured in 12-lead ECGs recorded at emergency room (initial ECG) (at a median of 55 minutes after VF onset), during 24-hour therapeutic hypothermia (TH) (TH-ECG), and at hospital discharge (discharge ECG). Results Among the 13 patients studied, 11 (84.6%) were categorized as non-diagnostic on the initial ECG, and a final diagnosis of ERS was established in 10 (76.9%) patients after the admission. All (10/10) ERS patients exhibited ER pattern and their peak J-point amplitude on the TH-ECG. Whereas, only 2 of the 10 (20%) ERS patients had ER pattern; 2 (20%), non-significant (<1 mm) ER pattern; and 6 (60%), no ER pattern on the initial ECG. Moreover, only 1 (10%) ERS patient showed ER pattern; 3 (30%), non-significant ER pattern; and 6 (60%), no ER pattern on the discharge ECG. Conclusions An absence of ER pattern on the initial/discharge ECG does not guarantee an exclusion of ERS in patients resuscitated from out-of-hospital VF. Indeed, 80/90％ of the ERS patients were non-diagnostic on admission/discharge ECG ("concealed" ERS). Thus, the "concealed ERS" may be misdiagnosed as idiopathic VF. ECG during TH (<24 hours after admission) may be important to make a correct diagnosis leading to specific therapies for ERS such as isoproterenol or quinidine.