Influence of epicardial stenosis severity and central venous pressure on the index of microcirculatory resistance in a follow-up study.

Aims: This study sought to evaluate the reproducibility of the index of microcirculatory resistance (IMR) in a follow-up model and the role of epicardial artery stenosis and central venous pressure (Pv) on IMR. Methods and results: Twenty-two patients with stable coronary artery disease underwent coronary catheterisation at baseline and after seven weeks. The IMR was calculated at baseline and follow-up in several ways: as IMRuncorrected=Pd center dot Tmn (Pd: intracoronary pressure distal to the stenosis; Tmn: transit mean time); IMRcorrected=Pa center dot Tmn center dot (Pd-Pw)/(Pa-Pw), (Pw: coronary wedge pressure; Pa: aortic pressure); and as IMRcentral venous pressure (IMRevp)=(Pa-Pv) center dot Tmn center dot (Pd-Pw)/(Pa-Pw). By neglecting Pw, IMR was overestimated irrespective of the haemodynamic severity of the epicardial stenosis (baseline: IMRuncorrected=15.5 +/- 8.9 U vs. IMRcorrected=13.5 +/- 8 U, p<0.001; follow-up: IMRuncorrected=16.9 +/- 4.9 U vs. IMRcorrected=13.8 +/- 4.6 U, p<0.001). In the intra-individual analysis IMR did not differ between the two time points. The IMRcvp equalled the IMRcorrected at all time points. Conclusions: IMR is a reproducible index in follow-up studies, independent of any overestimation existing when collateral flow status is neglected. Pv can be neglected for calculation of the IMR.