Assessment of fusion pacing on exercise capacity in patients with cardiac resynchronisation therapy devices
Authors: Green PG , Holdsworth D , Monteiro C , Betts T , Herring N 
Published: May 2022

Abstract

Funding Acknowledgements
Type of funding sources: Foundation. Main funding source(s): British Heart Foundation
Local Departmental Research Funding

Background
Cardiac resynchronisation therapy (CRT) using fusion pacing requires correct timing of left ventricular pacing to right ventricular activation. The SyncAV™ algorithm, achieves this by dynamic reassessment of intrinsic atrio-ventricular (AV) conduction to adjust the paced/sensed AV delay. However, it is unclear whether AV optimisation maintains resynchronisation during exercise, or whether loss of fusion could lead to decreased exercise capacity. Cardio-pulmonary exercise testing (CPET) is the gold standard method for assessing exercise performance and can provide prognostic information in the heart failure population.

Purpose
We therefore used CPET measures of exercise capacity to compare the SyncAV™ algorithm to conventional pacing with fixed AV delays, in a double blinded, randomised crossover study (NCT03768804).

Methods
Patients at least 6 months post-CRT implant performed 2 CPET tests at least 1 week apart, with randomisation to either SyncAV™ with fusion pacing or conventional biventricular pacing with a fixed AVD of 120ms. All other programming was optimised to produce the narrowest QRS duration possible at rest in each case.

Results
Twenty patients (11 male, age 71 [65-77] years, median [interquartile range]) were recruited, with both ischaemic and non-ischaemic aetiology of heart failure. All had clinical and/or echocardiographic response to CRT. Optimised Fixed AVD and SyncAV™programming resulted in similar narrowing of QRS duration (QRSd) from intrinsic rhythm at rest (131 [103-137] vs 134 [110-137] ms for fixed AVD and SyncAV™ groups respectively, p=0.85). Overall, there was no difference in peak oxygen consumption (V̇O2peak) between programming (14.91 [12.61-18.16] vs 15.61 [12.18-19.70] ml/kg/min, p=0.19), or oxygen consumption at anaerobic threshold (VT1) (7.36 [6.93-8.94] vs 7.87 [6.77-9.24] ml/kg/min, p=0.42), or in the time to reach either V̇O2PEAK (p=0.81) or VT1 (p=0.39). The BORG rating of perceived effort was also 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&lt;0.01). Eight were narrower with fixed AVD, 8 with SyncAV™ and in 4 there was no difference. 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 when programmed to the narrowest QRS duration at rest.

Conclusion
There is no significant difference in exercise capacity or QRSd between the use of optimised fixed AVD or SyncAV™, lending reassurance to fusion pacing being adequately maintained on exercise. In addition, programming with 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 supports the use of SyncAV™ in the 40% of patients where this gave the narrowest QRSd at rest.