Prediction of the true fractional flow reserve of left main coronary artery stenosis with concomitant downstream stenoses: in vitro and in vivo experiments.

AIMS: The functional impact of downstream coronary stenoses on left main coronary artery (LMCA) stenosis has not been fully elucidated. This study therefore aimed to use in vitro and in vivo experiments to assess two novel equations that predict the true fractional flow reserve (FFR) of a left main coronary artery (LMCA) stenosis with concomitant downstream stenoses. METHODS AND RESULTS: Two novel equations were derived. One equation predicts the true fractional flow reserve (FFR) of an LMCA stenosis with a downstream stenosis (Equation A), and the other predicts the true FFR of an LMCA stenosis with downstream stenoses in both the left anterior descending and left circumflex arteries (Equation B). The equations were validated in both in vitro and in vivo models of the coronary circulation. The agreements between the apparent FFR (FFRapp), the predicted FFR (FFRpred) and the true FFR (FFRtrue) were assessed by Passing-Bablok regression analysis. Passing-Bablok regression analysis revealed that there were fixed proportional errors between FFRapp-m and FFRtrue-m, though a very small fixed error and no proportional errors between FFRpred-m and FFRtrue-m. The absolute differences between FFRpred and FFRtrue were significantly lower as compared to those between FFRapp and FFRtrue in all experiments. CONCLUSIONS: Two novel equations which predict the true FFR of LMCA stenosis were demonstrated to be correct. The study also revealed that the functional impact of downstream stenoses on the LMCA stenosis became stronger when the downstream stenoses became more severe.