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BACKGROUND AND AIMS: Fusion pacing requires correct timing of left ventricular pacing to right ventricular activation, although it is unclear whether this is maintained when AV conduction changes during exercise. We used cardiopulmonary exercise testing (CPET) to compare cardiac resynchronization therapy (CRT) using fusion pacing or fixed atrioventricular delays (AVD). METHODS: Patients 6 months post-CRT implant with PR intervals less than 250 ms performed 2 CPET tests, using either the SyncAV™ algorithm or fixed AVD of 120 ms in a double blinded, randomised, crossover study. All other programming was optimised 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=0.85). Overall, there was no difference in peak oxygen consumption (V̇O2 PEAK , p=0.19), oxygen consumption at anaerobic threshold (VT1, p=0.42), or in the time to reach either V̇O2 PEAK (p=0.81) or VT1 (p=0.39). The BORG rating of perceived exertion was similar between groups. CPET performance was also analysed comparing whichever programming gave the narrowest QRSd at rest (119 [96-136] vs 134 [119-142] ms, p<0.01). QRSd during exercise (p=0.03), peak O2 pulse (ml/beat, a surrogate of stroke volume, p=0.03) and cardiac efficiency (watts/ml/kg/min, p=0.04) were significantly improved. CONCLUSION: Fusion pacing is maintained during exercise without impairing exercise capacity compared to 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. This article is protected by copyright. All rights reserved.

Original publication




Journal article


J Cardiovasc Electrophysiol

Publication Date



exercise, fusion, heart failure, pacing, resynchronisation