Clinical outcomes after upgrading from pacemakers to cardiac resynchronization therapy

Background and Aims: Right ventricular pacing may lead to heart failure (HF). Upgrades from pacemakers to cardiac resynchronization therapy (CRT) were excluded from most randomized, controlled trials. We sought to determine the long-term outcomes of upgrading from pacemakers to CRT with (CRT-D) or without (CRT-P) defibrillation in patients with no history of sustained ventricular arrhythmias. Methods and Results: In this observational study, clinical events were quantified in relation to the type of implant (de novo or upgrade) and device type at upgrade (CRT-P or CRT-D). Patients underwent CRT implantation (n = 1,545; 1,314 [85%] de novo implants and 231 [15%] upgrades) over a median of 4.6 years [interquartile range: 2.4 - 7.0]). In analyses of crude event rates, upgrades had a higher total mortality (adjusted hazard ratio [aHR]: 1.33; 95% confidence interval [CI] 0.10-1.61), a higher total mortality or HF hospitalization (aHR: 1.26; 95% CI 1.05-1.51), but similar mortality or hospitalization for major adverse cardiac events (MACEs, aHR: 1.15; 95% CI 0.96-1.38). No group differences emerged in any of these endpoints after propensity score matching. After inverse probability weighting in upgrades, total mortality (HR: 0.55; 95% CI 0.36-0.73), total mortality or HF hospitalization (HR: 0.56; 95% CI 0.34-0.79) and total mortality or hospitalization for MACEs (HR: 0.61; 95% CI 0.40-0.82) were lower after CRT-D than after CRT-P. Conclusion: Upgrading from pacemakers to CRT was associated with a similar long-term risk of mortality and morbidity to de novo CRT. After upgrade, CRT-D was CRT-D was associated with lower mortality than CRT-