BACKGROUND: The role of atrial pacing support is unclear in cardiac resynchronization therapy-defibrillator (CRT-D) patients without sinus node dysfunction. METHODS: We conducted a randomized, parallel-group, non-inferiority trial to evaluate whether a two-lead CRT-DX system capable of atrial sensing (but no pacing) via a floating dipole on the right ventricular lead is not inferior to a three-lead CRT-D with conventional atrial lead. Between October 17, 2018, and March 5, 2024, 636 patients (68 ± 10 years old, 28.6% females) with standard CRT-D indication, optimized medical therapy, and resting sinus rate ≥45 beats/min were randomized 1:1 to CRT-DX (VDD 35 beats/min) or CRT-D (DDD 50 beats/min) at 23 Italian sites. A centralized block randomization procedure stratified by site was used, with patients and primary outcome assessors blinded to treatment assignment. The primary endpoint was a 1-year composite of all-cause mortality, cardiovascular hospitalization, and lead-related complications (loss of functionality not correctable by device reprogramming). Key secondary endpoints were each component, echocardiographic reverse remodeling, and 6-minute walk test distance at 12 months. RESULTS: The primary endpoint occurred in 41 (13.1%) patients in the CRT-DX group and 47 (15.6%) patients in the CRT-D group, corresponding to a hazard ratio of 0.82 (95% CI, 0.54-1.25). This confirmed non-inferiority (pre-specified relative margin of 1.20) in both the per-protocol (p=0.039) and intention-to-treat (p=0.044) analyses. Individual components showed no significant differences, except for lead complications related to right atrial functionality (4 1.3% patients in the CRT-DX group vs. 13 4.2% patients in the CRT-D group; p=0.040). Reverse remodeling responders were 203 (77.5% of 262) CRT-DX patients and 190 (76.3% of 249) CRT-D patients (p=0.83). Walking distance did not differ between two study arms (404 vs. 398 m; p=0.62). After median follow-up of 2.4 years, only one CRT-DX patient required implantation of a standard atrial lead. CONCLUSIONS: Two-lead CRT-DX system without atrial pacing is non-inferior to conventional three-lead CRT-D, with fewer atrial lead-related complications.
“These results confirm what early pilot studies suggested—that, for the vast majority of CRT candidates, atrial pacing is not needed in the long term. By removing the atrial lead, CRT‑DX offers meaningful advantages in safety and procedure simplification without compromising clinical performance.”
Biffi et al. (2026) studied this question. A two-lead CRT-DX system without atrial pacing is non-inferior to conventional three-lead CRT-D and results in fewer atrial lead-related complications.
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