Looks can be deceiving: dissociation between angiographic severity and hemodynamic significance of a lesion. The importance of microvascular resistance

We present a case of an intermediate right coronary artery lesion with a fractional flow reserve (FFR) of 0.93 despite a myocardial perfusion scan demonstrating reversible ischemia in the inferior wall. An assessment of microvascular resistance was performed using the index of microcirculatory resistance (IMR). This was consistent with elevated resistance and may explain the discordance between the high FFR result, the positive perfusion study, and the lesion appearance on angiography. FFR assumes stable and minimal resistance at hyperemia; however, there may be situations where this does not occur, contributing to discrepant values. An understanding of the underlying physiological principles that underpin FFR is required for all physicians using this increasingly utilized technique.