Implantable cardioverter/defibrillator interventions in primary prevention: do current implantation criteria really predict ICD interventions?

Background Randomized controlled trials have proven the efficacy of implantable cardioverter/defibrillators (ICDs) to prevent sudden cardiac death (SO) in primary prevention. However, long-term data on the incidence of appropriate and inappropriate interventions in real life and on the predictive value of commonly used clinical variables to guide patient selection are scarce. Methods We retrospectively studied 101 patients who received an ICD for primary prophylaxis of SCD: 63.4% with ischaemic heart disease (IHD) and 36.6% with idiopathic dilated cardiomyopathy (IDCM). The mean follow-up period was 26.2 (+/- 14.8; median 27.8; range 5.6-70.5) months. Age, left ventricular ejection fraction (LVEF), QRS duration, NYHA class and electrophysiological study (EPS) outcome were evaluated as predictors of ICD intervention. Results At 2 years the cumulative incidence of appropriate (17.5% in IHD; 28% in IDCM; P=0.63) and inappropriate (12.8% in IHD, 15.4% in IDCM; P=0.62) interventions was similar in both groups. Atrial fibrillation was the most common cause of inappropriate interventions in the IHD group, sinus tachycardia in the IDCM group. Advanced age was associated with less inappropriate interventions (HR: 0.96 (95% confidence interval (CI) 0.94-0.98); P<0.01), and a better LVEF with less appropriate interventions (HR: 0.97 (95% CI 0.94-0.99); P<0.01). This amounted in a significant absolute difference in the number of appropriate interventions between the group with a LVEF <25% and 25-34% after 3 years of follow-up of 42% in IHD (48% vs 6%). A prolonged QRS duration was associated with a slightly elevated risk for appropriate interventions only in the IHD group (HR: 1.01 (95% CI 1.00-1.03); P=0.04). On the other hand, increased NYHA class was only associated with increased risk for appropriate interventions in the IDCM group (HR: 5.24 (95% CI 1.11-24.74); P=0.04). No significant statistical association was found between a positive EPS and appropriate or inappropriate interventions. Conclusions In primary prevention, during a mean follow-up of 2 years, one in five patients had a possibly live-saving appropriate intervention. However, the incidence of inappropriate interventions was substantial. Predictors for appropriate interventions were: (i) LVEF in the total study group, (ii) NYHA class in the IDCM group and (iii) QRS duration in the IHD group.