To Örebro University

Background: MODULAR ATP (antitachycardia pacing), a multicenter, international trial, assesses a modular cardiac rhythm management system (mCRM): a subcutaneous implantable cardioverter-defibrillator (S-ICD) in wireless communication with a leadless pacemaker (LP) capable of pace-terminating ventricular tachycardia (VT).

Methods: Enrolees had one or more clinical risk factors for VT and did not require chronic pacing. Complications included pre-specified major LP system- and procedure-related complications, and any complication related to the LP, S-ICD, implantation, or study protocol. Survival analysis was performed to identify complication-free rates, therapy delivery, and all-cause mortality.

Results: The 297 patients enrolled had an ejection fraction 35±13%, 43% secondary prevention indications, and 59% with prior ventricular arrhythmias (VA). Of 286 patients undergoing LP implantation (100% success), 251 patients completed 12-month follow-up. Mortality rate was 6%, with none related to the implant procedure. Median follow-up duration was 23.4 months (interquartile range: 17.9-28.1). The LP major complication-free rate was 97.2%, exceeding the performance goal. The overall LP+S-ICD system-related complication-free rate was 88.5%. Appropriate tachyarrhythmia-therapy (ATP+shock) rates were 14.4% and appropriate shock rates were 8.5%. Inappropriate total tachyarrhythmia therapy was 9.5% of which 8.5% were shocks. ATP was 67.3% successful in terminating VA episodes and accelerated VAs in 10.1% of episodes. Overall therapy burden (ATP+shock) was 96/100 patient-years of which 44/100 patient-years was for shock delivery.

Conclusions: One-year outcomes of the first modular pacing-defibrillator system reveal low system and LP complication rates and good ATP efficacy rates suggesting that the mCRM is a viable alternative to single-chamber ICDs using low-energy pacing capability without the need for transvenous leads.