Left Ventricular Endocardial or Triventricular Pacing to Optimize Cardiac 1 Resynchronization Therapy in a Chronic Canine Model of Ischemic Heart

20 Background: Cardiac resynchronization therapy (CRT) is a proven treatment for heart failure 21 but approximately 30% of patients appear to not benefit from the therapy. Left ventricular (LV) 22 endocardial and multisite epicardial (TriV) pacing have been proposed as alternatives to 23 traditional LV transvenous epicardial pacing, but no study has directly compared the 24 hemodynamic effects of these approaches. 25 Methods and Results: Left bundle branch block ablation and repeated microembolizations were 26 performed in dogs to induce electrical dysynchrony and to reduce LV ejection fraction to less 27 than 35%. LV dP/dtmax and other hemodynamic indices were measured with a conductance 28 catheter during LV epicardial, LV endocardial, Biventricular (BiV) epicardial, BiV endocardial 29 and TriV pacing performed at 3 atrioventricular delays. LV endocardial pacing was obtained 30 with a clinically-available pacing system. The optimal site was defined as the site that increased 31 dP/dtmax by the largest percentage. Implantation of the endocardial lead was feasible in all 32 canines (n=8) without increased mitral regurgitation seen with transesophageal echocardiography 33 and with full access to the different LV endocardial pacing sites. BiV endocardial pacing 34 increased dP/dtmax more than BiV epicardial and TriV pacing on average (p<.01) and at the 35 optimal site (p<.01). There were no significant differences between BiV epicardial and TriV 36 pacing. 37 Conclusions: BiV endocardial pacing was superior to BiV epicardial and to TriV pacing in terms 38 of acute hemodynamic response. Further investigation is needed to confirm the chronic benefit of 39 this approach in humans. 40 41