Mortality implications of appropriate implantable cardioverter defibrillator therapy in secondary prevention patients: contrasting mortality in primary prevention patients from a prospective population-based registry

Background — We sought to examine the mortality impact of appropriate implantable cardioverter defibrillator (ICD) therapy between patients who received ICD for primary versus secondary prevention purposes.

Methods and Results — From a prospective, population‐based registry, we identified 7020 patients who underwent de novo ICD implantation between February 2007 and May 2012 in Ontario, Canada. The primary outcome was all‐cause mortality. We used multivariable Cox proportional hazard modeling to adjust for differences in baseline characteristics and analyzed the mortality impact of first appropriate ICD therapy (shock and antitachycardia pacing [ATP]) as a time‐varying covariate. There were 1929 (27.5%) patients who received ICDs for secondary prevention purposes. The median follow‐up period was 5.02 years. Compared with those with secondary prevention ICDs, patients with primary prevention ICDs had more medical comorbidities, and lower ejection fraction. Patients who experienced appropriate ICD shock or ATP had greater risk of death compared with those who did not, irrespective of implant indication. In the primary prevention group, the adjusted hazard ratios of death for appropriate shock and ATP were 2.00 (95% CI: 1.72–2.33) and 1.73 (95% CI: 1.52–1.97), respectively. In the secondary prevention group, the adjusted hazard ratios of death for appropriate ICD shock and ATP were 1.46 (95% CI: 1.20–1.77) and 1.38 (95% CI: 1.16–1.64), respectively.

Conclusions — Despite having a more favorable clinical profile, occurrence of appropriate ICD shock or ATP in patients with secondary prevention ICDs was associated with similar magnitudes of mortality risk as those with primary prevention ICDs. A heightened degree of care is warranted for all patients who experience appropriate ICD shock or ATP therapy.