Automated Implantable Cardiac Defibrillator: A Competing Risks Analysis

Background: The advent of the Automated Implantable Cardiac Defibrillator (AICD) has transformed the prevention of sudden cardiac death. This lifesaving potential has to be weighed against procedural and device-related complications, inappropriate shocks, and health economy considerations. With advancing age and comorbidity burden, competing death may diminish benefit in a cohort of patients implanted with devices. Methods: Patients with ischaemic and non-ischaemic cardiomyopathy, with ICDs implanted from 1994 until 2008 for either primary or secondary indications, were followed in a multi-centre registry. Fine and gray competing risks regression models were fitted to identify predictors of time to first appropriate therapy and time to death without an appropriate event. For each of these outcomes, the following predictors were considered in univariate and then multivariate analyses: primary vs. secondary prevention, gender, age, ejection fraction, ischaemic vs. non-ischaemic, beta blocker use, atrial fibrillation and AICD type (single, dual or biventricular). Results: A total of 396 patients were included for final analysis. The mean follow-up time was 3.5 ± 2.8 years (range 0.8–15 years). Two thirds of devices were for ischaemic cardiomyopathy (269, 67.9%) with over half of devices indicated for secondary prevention (207, 52.3%). One third of patients received appropriate therapy with mean time to first appropriate event 14.5 ± 19.6 months. In competing risk analyses, age was the only predictor of death occurring prior to appropriate therapy (HR, 1.06 per year, 95% CI 1.02–1.07; p < 0.001). Indication for primary prevention was a strong predictor in those who did not receive therapy (OR, 6.39, 95% CI 4.01–10.19; p < 0.001). Conclusion: In this cohort of Australian AICD therapy, secondary prevention patients were five times more likely to receive a potentially lifesaving therapy than primary prevention patients. Furthermore for every 10 years of advancing age, the risk of death prior to any appropriate device therapy increased by 79%.