Experimental validation of pulse contour methods for estimating stroke volume at pacing onset

Stroke volume (SV) might be an important variable in assessing cardiac function of patients under pacing therapy. To assess the accuracy of estimating SV changes from aortic pressure during VDD pacing, we implanted electromagnetic flowmeters in the aortic root of five mongrel dogs. Three pacing sites, including right ventricle, left ventricle and both ventricles were selected and paced at 5 atrioventricular delays. Each pacing site/AV delay combination was repeated 5 times in a randomized order. The protocol alternated 5 paced beats and 15 intrinsic beats. Flow and aortic pressure data were recorded and analyzed. We evaluated five pulse contour equations relating pulse pressure (PP), ejection time (ET), diastolic time (DT) and aortic pressure area during systole over the end-diastolic pressure (Psa). A good correlation (r=0.84-0.89) was shown between percent change in SV and percent change in PP, PP*ET, Psa, Psa*ET and Psa*(1+ET/DT) over the preceding baseline. The average estimated percent change in SV also correlated with the average measured percent change in SV for each pacing site/AV delay combination. In conclusion, PP, PP*ET, Psa, Psa*ET and Psa*(1+ET/DT) may be clinically applicable for assessing SV at the start of VDD pacing and may effectively predict the effects of pacing sites and AV delays on SV