Mechanistic insights into the benefits of multisite pacing in cardiac resynchronization therapy: The importance of electrical substrate and rate of left ventricular activation

BackgroundMultisite pacing (MSP) of the left ventricle is proposed as an alternative to conventional single-site LV pacing in cardiac resynchronization therapy (CRT). Reports on the benefits of MSP have been conflicting. A paradigm whereby not all patients derive benefit from MSP is emerging.ObjectiveWe sought to compare the hemodynamic and electrical effects of MSP with the aim of identifying a subgroup of patients more likely to derive benefit from MSP.MethodsSixteen patients with implanted CRT systems incorporating a quadripolar LV pacing lead were studied. Invasive hemodynamic and electroanatomic assessment was performed during the following rhythms: baseline (non-CRT); biventricular (BIV) pacing delivered via the implanted CRT system (BIVimplanted); BIV pacing delivered via an alternative temporary LV lead (BIValternative); dual-vein MSP delivered via 2 LV leads; MultiPoint Pacing delivered via 2 vectors of the quadripolar LV lead.ResultsSeven patients had an acute hemodynamic response (AHR) of <10% over baseline rhythm with BIVimplanted and were deemed nonresponders. AHR in responders vs nonresponders was 21.4% ± 10.4% vs 2.0% ± 5.2% (P < .001). In responders, neither form of MSP provided incremental hemodynamic benefit over BIVimplanted. Dual-vein MSP (8.8% ± 5.7%; P = .036 vs BIVimplanted) and MultiPoint Pacing (10.0% ± 12.2%; P = .064 vs BIVimplanted) both improved AHR in nonresponders. Seven of 9 responders to BIVimplanted had LV endocardial activation characterized by a functional line of block during intrinsic rhythm that was abolished with BIV pacing. All these patients met strict criteria for left bundle branch block (LBBB). No nonresponders exhibited this line of block or met strict criteria for LBBB.ConclusionPatients not meeting strict criteria for LBBB appear most likely to derive benefit from MSP.