AIMS: Assessment of the coronary circulation has largely been based on pressure ratios (epicardial-) and resistance (micro-vessels). Simultaneous assessment of epicardial- (CEPI) and microvascular conductance (CMICRO) provides an intuitive approach using the same units for both compartments and expressing the actual deliverability of blood. The aim of study was to develop a novel integral method to assessing the functional severity of epicardial and microvascular disease.
METHODS AND RESULTS: We performed intracoronary Doppler and pressure in 403 vessels in 261 stable patients. Hyperaemic mid-to-late diastolic pressure and flow velocity (PV) relationships were calculated. The slope of the aortic PV indicates the overall conductance and the slope of the distal PV relationship represents CMICRO. The intercept with the x-axis represents zero-flow pressure (Pzf). CEPI was derived from microvascular- and overall conductance. Median CEPI was higher compared to CMICRO (4.2 [2.1-8.0] versus 1.3 [1.0-1.7] cm/s/mmHg, p<0.001). CMICRO was independent of stenosis severity (1.3 [1.0-1.7] in FFR≤0.80 versus 1.4 [1.0-1.8] in FFR>0.8, p=0.797). ROC curves (using FFR and HSR concordant vessels as standard) demonstrated an excellent ability of CEPI to characterize significant stenoses (AUC 0.93). When CEPI<CMICRO, we demonstrate a decrease in flow velocity and coronary pressure (optimal cutoff value 0.97, AUC 0.90).
CONCLUSIONS: A comprehensive assessment of separate CEPI and CMICRO was feasible. CEPI has a remarkable diagnostic efficiency to detect a clinically relevant stenosis. When CEPI<CMICRO, distal flow and pressure decrease steeply, indicating myocardial ischemia. CMICRO can be used to explore the severity of microvascular disease.