Risk of subsequent ventricular arrhythmia is higher in primary prevention patients with implantable cardioverter defibrillator than in secondary prevention patients.

Background: Because of previous ventricular arrhythmia (VA) episodes, patients with implantable cardioverter-defibrillator (ICD) for secondary prevention (SP) are generally considered to have a higher burden of VAs than primary prevention (PP) patients. However, when PP patients experienced VA, the difference in the prognosis of these two patient groups was unknown.
Methods: The clinical characteristics and follow-up data of 835 ICD patients (364 SP patients and 471 PP patients) with home monitoring feature were retrospectively analysed. The incidence rate and risk of subsequent VA and all-cause mortality were compared between PP patients after the first appropriate ICD therapy and SP patients.
Results: During a mean follow-up of 44.72 ± 20.87 months, 210 (44.59%) PP patients underwent appropriate ICD therapy. In the Kaplan-Meier survival analysis, the PP patients after appropriate ICD therapy were more prone to VA recurrence and all-cause mortality than SP patients (P<0.001 for both endpoints). The rate of appropriate ICD therapy and all-cause mortality in PP patients after the first appropriate ICD therapy was significantly higher than that in SP patients (for device therapy, 59.46 vs 20.64 patients per 100 patient-years; incidence rate ratio [IRR] 2.880, 95% confidence interval [CI]: 2.305-3.599; P<0.001; for all-cause mortality, 14.08 vs 5.40 deaths per 100 patient-years; IRR 2.607, 95% CI: 1.884-3.606; P<0.001). After propensity score matching for baseline characteristics, the risk of VA recurrence in PP patients with appropriate ICD therapy was still higher than that in SP patients (41.80 vs 19.10 patients per 100 patient-years; IRR 2.491, 95% CI: 1.889-3.287; P<0.001), but all-cause mortality rates were similar between the two groups (12.61 vs 9.33 deaths per 100 patient-years; IRR 1.352, 95% CI: 0.927-1.972; P = 0.117).
Conclusions: Once PP patients undergo appropriate ICD therapy, they will be more prone to VA recurrence and death than SP patients.