Cardiac resynchronization using fusion pacing during exercise

J Cardiovasc Electrophysiol. 2024 Jan;35(1):146-154. doi: 10.1111/jce.16120. Epub 2023 Nov 27.


Introduction: Fusion pacing requires correct timing of left ventricular pacing to right ventricular activation, although it is unclear whether this is maintained when atrioventricular (AV) conduction changes during exercise. We used cardiopulmonary exercise testing (CPET) to compare cardiac resynchronization therapy (CRT) using fusion pacing or fixed AV delays (AVD).

Methods: Patients 6 months post-CRT implant with PR intervals < 250 ms performed two CPET tests, using either the SyncAV™ algorithm or fixed AVD of 120 ms in a double-blinded, randomized, crossover study. All other programming was optimized to produce the narrowest QRS duration (QRSd) possible.

Results: Twenty patients (11 male, age 71 [65-77] years) were recruited. Fixed AVD and fusion programming resulted in similar narrowing of QRSd from intrinsic rhythm at rest (p = .85). Overall, there was no difference in peak oxygen consumption (V̇O2 PEAK , p = .19), oxygen consumption at anaerobic threshold (VT1, p = .42), or in the time to reach either V̇O2 PEAK (p = .81) or VT1 (p = .39). The BORG rating of perceived exertion was similar between groups. CPET performance was also analyzed comparing whichever programming gave the narrowest QRSd at rest (119 [96-136] vs. 134 [119-142] ms, p < .01). QRSd during exercise (p = .03), peak O2 pulse (mL/beat, a surrogate of stroke volume, p = .03), and cardiac efficiency (watts/mL/kg/min, p = .04) were significantly improved.

Conclusion: Fusion pacing is maintained during exercise without impairing exercise capacity compared with fixed AVD. However, using whichever algorithm gives the narrowest QRSd at rest is associated with a narrower QRSd during exercise, higher peak stroke volume, and improved cardiac efficiency.

Keywords: exercise; fusion; heart failure; pacing; resynchronization.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Cardiac Resynchronization Therapy Devices
  • Cardiac Resynchronization Therapy* / adverse effects
  • Cardiac Resynchronization Therapy* / methods
  • Cross-Over Studies
  • Electrocardiography
  • Heart Failure* / diagnosis
  • Heart Failure* / therapy
  • Heart Rate
  • Humans
  • Male
  • Treatment Outcome