Electrical Storm as an Independent Mortality Risk in Patients with Preserved or Moderately Reduced Left Ventricular Function

Electrical storm (ES), defined by 3 or more occurrences of ventricular arrhythmias within 24 hours, has been shown to be associated with an increased risk of mortality; however, detailed information remains lacking. We aimed to examine the incidence and determinants of ES and its impact on mortality in patients enrolled in the nationwide implantable cardioverter-defibrillator (ICD) registry. We studied 1,256 patients (age 65 +/- 12 years) who had structural heart disease with an ICD. The patients were classified into reduced ejection fraction (EF < 35%; 657 (52%) patients) and preserved or moderately reduced EF (EF >= 35%; 599 (48%) patients). ES occurred in 49 (7%) and 36 (6%) patients in the EF < 35% and EF >= 35% groups (log-rank P = 0.297) during the median follow-up of 2.3 years. ICD with resynchronization therapy was associated with a lower incidence of ES in patients with EF < 35%. Non-ischemic heart disease and diuretics were associated with ES in patients with EF >= 35%. During the follow-up, 10/49 (20%) patients with ES and 80/608 patients (13%) without ES died in patients with EF < 35%, while 7/36 (19%) patients with ES and 38/563 patients (7%) without ES died in those with EF >= 35%. We have created 4 Cox multivariate models. All models showed approximately 2-fold higher hazard ratios in patients with EF >= 35% compared to EF < 35%. Our study showed that the determinants of ES differed between EF < 35% and EF >= 35%. The impact of ES for mortality was numerically higher in EF >= 35% than in EF < 35%, although a significant interaction was not detected.