Misinterpretation of Functional Severity of Coronary Stenosis in the Presence of Collateral Flow

Angiography is widely used diagnostic method to find the ischemic severity. However, it is limited in its capacity in determining the functional severity of the stenosis [1]. Hence, a functional diagnostic parameter Fractional Flow Reserve (FFR), defined as the ratio of distal pressure to the proximal pressure at maximum vasodilation [2], at the site of the stenosis, was developed to assess the functional severity of the stenosis. Pijls et al [3], established a threshold value of 0.75 for FFR, based on which coronary intervention decisions are taken. If FFR is below 0.75, a percutaneous coronary intervention is recommended. FFR is calculated during cardiac catheterization by measuring the pressure values across the stenosis. However, the value of FFR measured during cardiac catheterization doesn’t account for the increase in pressure values downstream of stenosis, due to other resistances in coronary circuit, e.g., abnormal microvasculature and functional collaterals, as it cannot delineate the effect of downstream collateral flow or the presence of myocardial diseases.