Assessment of Microcirculatory Remodeling With Intracoronary Flow Velocity and Pressure Measurements

Background— Intracoronary physiology techniques have been validated extensively for the assessment of epicardial stenoses but not for the lone study of coronary microcirculation. We performed a comparison between 4 intracoronary physiological indices with the actual structural microcirculatory changes documented in transplanted hearts. Methods and Results— In 17 cardiac allograft patients without coronary stenoses, ECG, intracoronary Doppler flow velocity, and aortic pressure were digitally recorded before and during maximal hyperemia with a dedicated system. Postprocessing of data yielded 4 indices of microcirculatory status: coronary flow velocity reserve (2.13±0.59), instantaneous hyperemic diastolic velocity pressure slope (2.33±1.25 cm · s · −1 mm Hg −1 ), coronary resistance index (1.65±0.88 mm Hg · cm −1 · s −1 ), and coronary resistance reserve (2.36±0.65). Quantitative morphometry was performed in endomyocardial biopsies during the same hospital intake; arteriolar obliteration (76.57±6.95%) and density (2.00±1.22 arterioles per 1 mm 2 ) and capillary density (645±179 capillaries per 1 mm 2 ) were measured. Univariate regression analysis between intracoronary measurements and histological findings revealed that instantaneous hyperemic diastolic velocity-pressure slope correlated with arteriolar obliteration ( r =0.58, P =0.014) and capillary density ( r =0.60, P =0.012). Statistical adjustment revealed an independent contribution of arteriolar obliteration (β=0.61, P =0.0009) and capillary density (β=−0.60, P =0.0008) to instantaneous hyperemic diastolic velocity-pressure slope values, resulting in an excellent predictive model ( r =0.84, P =0.0002). Coronary resistance index correlated only with capillary density ( r =0.70, P =0.019). Relative indices (coronary flow velocity reserve and coronary resistance reserve) did not correlate significantly with arteriolar obliteration, capillary density, or arteriolar density. Conclusions— Intracoronary indices derived from pressure and flow, particularly instantaneous hyperemic diastolic velocity-pressure slope, appear to be superior to coronary flow velocity reserve in detecting structural microcirculatory changes. Both arteriolar obliteration and capillary rarefaction seem to influence microcirculatory hemodynamics independently.