Frequency of Need for Antitachycardia or Antibradycardia Pacing or Cardiac Resynchronization Therapy in Patients With a Single-Chamber Implantable Cardioverter-Defibrillator

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is unable to deliver antitachycardia pacing (ATP), bradycardia pacing, and cardiac resynchronization therapy (CRT). However, little is known about the proportion of patients that develop the need for 1 of these features. We evaluated the potential suitability for a S-ICD at the time of first replacement in a cohort of patients with a transvenous single-chamber device who did not need bradycardia pacing at the time of implantation. The study cohort consisted of patients who received a transvenous single-chamber ICD between 1998 and September 2017. The primary end point was a combined end point of the need for atrial or ventricular pacing, development of a CRT indication, or termination of ventricular arrhythmias by ATP delivery. During a mean follow-up of 5.6 ± 1.9 years, 78 of 254 patients (31%) reached the primary end point. The 7 years' cumulative S-ICD suitability rate was 65.6% (95% confidence interval [CI] 58.5% to 71.7%). Event rates were 9.5% (95% CI 6.5% to 13.9%) at 1-year follow-up, and 28.0% (95% CI 22.8% to 34.2%) at 5 years' follow-up. For individual end points, incidence rates were 1.8 (95% CI 1.2 to 2.6) per 100-patient-years for CRT, 0.3 (95% CI 0.1 to 0.8) per 100-patient-years for pacing-dependency, and 4.9 (95% CI 3.8 to 6.3) per 100-patient-years for appropriate ATP therapy. No baseline variables for predicting S-ICD unsuitability were found. In conclusion, at the time of the first replacement, 69% of the patients with a single-chamber device would have been clinically eligible for the S-ICD. Incidence rates of developing a bradycardia pacing and CRT indication are low.