Introduction: 

Conventional right ventricular (RV) apex pacing is associated with asynchronous activation, reduced left ventricular (LV) pump function and increased risk for development of heart failure. We investigated whether pacing at alternative sites can maintain a better cardiac pump function as well as mechano-energetic efficiency of the heart.

Methods: 

After AV-nodal ablation, mongrel dogs were randomized to receive 16 weeks of VDD pacing at the RV apex (RVa, n = 9), RV septum (RVs, n=7), LV apex (LVa, n = 7), or LV septum (LVs, n = 8). LVs paced animal received a modification of the Medtronic 3830 pacing lead, with extended helix) which was introduced transvenously and, after positioning against the RV septum using a pre-shaped guiding catheter, driven into the interventricular septum by rotation of the screw-in lead until the LV endocardium ; a trans-ventricular septal approach). During atrial pacing (AP) with normal ventricular conduction and after 1-3 hours and 16 weeks of ventricular pacing we measured contractility (dP/dtmax, normalized to instantaneous pressure), relaxation (time constant of LV pressure fall) and stroke work (SW) using conductance catheters. At these times also myocardial oxygen consumption (MVO2) was measured. At 16 weeks, MRI tagging was performed to measure mechanical dyssynchrony and discoordination from myocardial strains.

Results: 

While acute and chronic RVa and RVs apex pacing significantly reduced contractility and relaxation, LVs and LVa pacing maintained these parameters near AP levels. RVa and RVs pacing also reduced mechanical efficiency (SW/ MVO2) and increased mechanical dyssynchrony and discoordination., whereas LVs and LVa pacing maintained the normal efficiency and coordination.

Conclusions: 

Chronic LVa and LVs pacing maintain LV contractility and mechano-energetic efficiency near normal levels, and at a higher level than RVa and RVs pacing. Therefore, using a good site of pacing the heart can pump better at a higher efficiency.