Abstract 2162: Mechano-energetic Superiority Of Left Ventricular Apex And Left Ventricular Septal Pacing

Abstract

Objective: Previous studies showed hemodynamic benefits over right ventricular (RV) apex pacing by left ventricular (LV) septal or LV apex pacing. We investigated whether this benefit is also reflected in mechanical efficiency. Methods: After AV-nodal ablation, dogs received 16 weeks of VDD pacing at the RV apex (RVa; n = 8), LV apex (LVa; n = 7) or LV septum (LVs; n = 8; transventricular-septal approach). After chronic pacing, LV stroke work (SW; conductance catheter) was measured, as well as relative myocardial oxygen consumption (MVO 2 , coronary flow velocity and arterial-coronary sinus O 2 difference). Baseline efficiency (SW/MVO 2 ) was assessed during implant site (IS), RVa, LVa, and RVa + LV lateral (BiV) pacing. In order to investigate the effect of pacing site udner different conditions, measurements were performed during baseline and dobutamine infusion +/− partial aortic occlusion. The O 2 cost of generating SW, corrected for end-systolic elastance and effective arterial elastance, was calculated using the Suga model of mechano-energetics. Results: RVa pacing after chronic LV pacing reduced SW/MVO 2 (Figure a ; mean ± SD, *p<0.05 vs. 1) and increased O 2 cost (Figure b ) in combination with a 12% fall in LV dP/dt-max. However, LVa or BiV pacing after chronic RVa pacing did not significantly alter efficiency, despite a 12% increase in LV dP/dt-max. LVa pacing improved efficiency over LVs and collectively over BiV pacing (p<0.05). Conclusions: Acutely, LVa pacing results in the greatest mechanical efficiency. The lack of improvement in efficiency despite increasing contractility when switching from chronic RVa pacing to LV based pacing may indicate contractile remodeling.