Influence of pacing site on left ventricular performance: Rationale for positioning of pacing leads?

Objectives: Optimal pacing sites have been shown to improve cardiac performance in small animal experiments, whereas pump function can be impaired by suboptimal ventricular pacing. This study was conducted to evaluate the optimal lead placing for the improvement of left ventricular performance. Material and Methods: Pacing was performed in an in-situ porcine ventricular pacing model with complete AV-block (n=10). Temporary ventricular leads at 3 different sites at the right (outflow tract, margin and base) and left ventricle (outflow tract, margin and base) stimulated the heart with 80 and 120 beats per minute. Placing of electrodes was standardized using Ramus interventricularis anterior and posterior as orientation. Aortic flow, blood pressure and left atrial pressure were acquired. Cardiac performance was assessed by means of a conductance catheter (pressure-volume relations). Preload and afterload of the left ventricle were held constant by volume substitution. No positive or negative inotropic agents were used. Impulse amplitude and frequency were kept constant at all times. Results: In terms of pressure-volume-loops, cardiac output and aortic flow and pressure, pacing close to the right ventricular (RV) apex was superior to right ventricular outflow tract and base (p<0,05). Pacing at the left ventricular (LV) apex was superior to left outflow tract and base (p<0,05). LV performance was significantly better in LV-pacing compared to RV-pacing (p<0,05). Conclusions: Despite the limitation of the animal model with normal hearts, there was a clear effect of positioning pacing leads. The conductance catheter technology is an adequate tool to optimize lead positioning in pathological altered human ventricular myocardium.