Prevalence, circumstances, mechanisms, and risk stratification of sudden cardiac death in unipolar single-chamber ventricular pacing.

BACKGROUND: Permanent cardiac pacing is well established for the improvement of prognosis and quality of life in patients with severe bradycardia. However, sudden cardiac death still remains an unresolved problem, as it occurs in approximately 20-30% of paced patients. This 2-year follow-up study was directed at prospectively assessing prevalence, circumstances, and mechanisms of sudden death in 2,021 permanently paced patients. METHODS AND RESULTS: During the observation period, 220 patients (11%) died (mean pacing interval, 50.5 +/- 7 months). Lethal cerebrovascular events in 66 of 220 patients (30%) and sudden death in 49 of 220 patients (23%) were the two most frequently reported modes of death. Nonsudden (first year, 20%; subsequent years, 6.9%; p less than 0.01) and sudden death mortality rate (4% versus 1.8%, p less than 0.05) were highest during the first year. Mortality was unrelated to the patient's activity status at the time of death. Sudden cardiac death occurred more often in male patients (increased risk, 1.7 versus female patients; p less than 0.001) and patients younger than 60 years of age (5.2 versus patients older than 60 years, p less than 0.001). Patients with severe bradycardia (sudden death rate, 28%), severe atrioventricular block (25%), or atrial fibrillation with low ventricular rate (25%) before pacemaker implantation were more likely to suffer from sudden cardiac death than patients with previous syncopal attacks (sudden death rate, 15%) or sick sinus syndrome (17%). The highest incidence of sudden death was observed in patients with bifascicular and trifascicular bundle branch block. In this group, 35% of patients died suddenly during the follow-up period compared with 18% of patients without bundle branch block. In a subsequent study in 90 consecutive patients with various types of bundle branch block, undersensing of up to 13% of ectopic ventricular beats occurred in patients with bifascicular block. Pacing-induced tachyarrhythmias and ventricular fibrillation were documented in 10% of undersensed ectopic ventricular beats as well as in the setting of atrial fibrillation associated with ventricular arrhythmias. CONCLUSIONS: Young age, male sex, and a severely diseased heart indicated by the presence of bifascicular and trifascicular bundle branch block are the strongest predictive clinical parameters for sudden cardiac death, especially in the first year after pacemaker implantation.