Assessment of fusion pacing on exercise capacity in patients with cardiac resynchronisation therapy devices

Abstract

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 (V?O2peak) 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 VO2PEAK (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<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. ™, 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.