Comparison of second appropriate defibrillator therapy occurrence in patients implanted for primary prevention and secondary prevention – Sub-analysis of the Nippon Storm Study-

Background: Patients with implantable cardioverter defibrillator (ICD) use for primary prevention (primary prevention patients) of sudden cardiac death have lower incidence of appropriate ICD therapy (app-Tx) compared with those with ICD use for secondary prevention (secondary prevention patients). However, detail analysis of a second app-Tx after a first app-Tx is still lacking. Objective: This study aimed to compare the incidence of a second app-Tx in primary vs secondary prevention patients. Methods: We conducted sub-analysis of the Nippon Storm Study, which was a prospective, observational study involving 985 patients with structural heart disease (left ventricular ejection fraction ≤ 50%). Of these, we selected 251 patients (62 ± 14 years old, 82% men) who experienced at least one appropriate ICD therapy, and compared occurrence of a second app-Tx between primary (n = 116) and secondary (n = 135) prevention patients. Results: There was no significant difference in the incidence of a second app-Tx between primary and secondary prevention patients (the cumulative incidence for a second app-Tx was 59% at 1 year and 79% at 3 years in primary prevention patients vs the cumulative incidence for the second app-Tx was 59% at 1 year and 75% at 3 years in secondary prevention patients). Additionally, we evaluated the incidence of a second app-Tx according to basal structural disease (ischemic and non-ischemic cardiomyopathy) and found no significant difference between primary and secondary prevention patients. Conclusion: Once app-Tx occurs, primary prevention patients acquire the high risk of subsequent ventricular arrhythmias because there is a comparable incidence of a second app-Tx in secondary prevention patients.