Effect of site and intensity of pacing on left ventricular performance

The effect of pacing site and intensity on left ventricular performance is examined. The maximal value of left ventricular developed pressure (PD) and the peak (dp/dt) /P (Vpm) were followed in 11 anesthetized dogs. The following sites were paced: atrial (A), simultaneous atrial and right ventricular (RV), simultaneous atrial, right and left ventricular (RLV) and simultaneous atrial and left ventricular (LV)(, while varying the rate from sinus rate up to 350/min and the intensity from threshold up to 20-120 mA. When all 4 sites were paced in the same experiment, the A pacing resulted in the highest values of Vpm and PD while RV pacing resulted in the lowest values. The higher the pacing intensity the higher the Vpm and PD values tended to be. The strongest correlation coefficient was observed between Vpm and intensity on RV pacing while the same correlation on LV or Rv pacing and between PD and intensity on LV pacing were not significant at the 5% level. On RV pacing a low (les than 0.85) Vpm ratio (Vpm on RV pacing expressed over Vpm on A pacing at the same frequency and intensity) was associated with 65% of 129 pacing runs at a relatively low (less than 35 mA) intensity but with only 35% of 91 runs at a higher intensity (X2 = 19,20, p less than 0.001). The effect of pacing site and intensity on Vpm tended to be more pronounced at faster than at slower pacing frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)