Aims: To evaluate the incidences of and risk factors predisposing to appropriate and inappropriate shocks and mortality in a 'real-world' population of patients with ischaemic heart disease (IHD) and implantable cardioverter defibrillators (ICD) for primary prevention of sudden cardiac death (SCD).
Methods and results: In this nationwide cohort, we prospectively followed 1609 patients with IHD and left ventricular dysfunction from the Danish ICD Register who received an ICD for primary prevention of SCD (1 January 2007 to 30 November 2011). Primary study outcomes were appropriate shocks, inappropriate shocks, and all-cause mortality. Secondary study outcomes included the composite endpoints: appropriate therapy and inappropriate therapy (defined as shock or anti-tachycardia pacing). All-cause mortality was 12.1% during a mean follow-up time of 1.9 ± 1.3 years. Inappropriate shocks and therapy occurred in 2.6% and 3.7% during follow-up, respectively. Appropriate shocks and therapy was identified in 7.8% and 13.4%, respectively. Time-dependent multivariable Cox regression analyses were used to identify risk factors of inappropriate/appropriate shock, therapy and mortality. Implantation of a dual-chamber ICD was associated with increased risk of both inappropriate shocks and any inappropriate therapy compared to single-chamber ICD [hazard ratios (HR) = 2.45; confidence intervals (CI):1.16-5.14 and HR = 2.38; CI:1.28-4.42, respectively]. No excess risk of mortality was associated with any device type.
Conclusion: In this nationwide study of IHD patients with an ICD for primary prevention of SCD, the incidence of appropriate shocks as well as inappropriate shocks were significantly lower than reported in randomized trials. Implantation of a dual-chamber ICD was associated with more inappropriate shocks compared with single chamber devices.
Keywords: CRT-D; ICD; Ischaemic heart disease; Primary prevention.