Variability of Microcirculatory Resistance Index and Its Relationship With Fractional Flow Reserve in Patients With Intermediate Coronary Artery Lesions

BACKGROUND: The relationship between the functional significance of epicardial coronary artery stenosis and microvascular resistance remains to be determined. Furthermore, little is known regarding the determinants of microvascular resistance in patients with intermediate coronary lesions. METHODS AND RESULTS: Using a pressure-temperature sensor-tipped guidewire, thermodilution-derived index of microcirculatory resistance (IMR) was measured, along with fractional flow reserve (FFR), in 131 coronary arteries of 104 patients with intermediate stenosis, in order to determine the relationship between IMR and clinical data. IMR varied widely (median, 20.8; range, 6.3-65.2), and no significant relationship was observed between IMR and FFR after IMR was corrected for coronary wedge pressure in the territories with functionally significant stenoses. There was no significant relationship between IMR and Framingham risk score, systematic coronary risk evaluation (SCORE), ACC/AHA lesion classification, or SYNTAX score. Right coronary artery (RCA) lesion location and history of hypertension were significantly associated with increased IMR. Multivariate analysis showed that RCA lesion location (odds ratio [OR], 4.52; 95% confidence interval [CI]: 1.84-11.11, P=0.001) and hypertension (OR, 3.03; 95% CI: 1.15-7.96, P=0.025) were independent predictors of increased IMR. CONCLUSIONS: Functional significance of intermediate coronary stenosis was not correlated with microvascular resistance of the perfusion territory. Intermediate coronary lesions may result in increased microcirculatory resistance irrespective of functional significance of the stenosis, with significant regional difference in microvascular resistance.