Effect of Arterial Distensibility and Stenoses on Pressure Drop in Pulsatile Flow

The most accepted standard tool of cardiologists for assessing stenoses severity in the coronary tree is coronary angiography. Information from coronary angiography is limited to geometrical data on the coronary lumen, and provides limited functional data on the severity of stenoses. In addition, histopathological studies have demonstrated that angiographic evidence of stenosis is usually detected when the cross-sectional area of a plaque approaches 40% to 50% of the total cross-sectional area of the vessel [1]. Hence, managing the intermediate coronary lesions (40% to 70% diameter stenosis) are a true challenge for cardiologists. These geometrical limitations have led to the development of several hemodynamic parameters, which functionally assess stenoses severity and the cardiovascular tree, among which the most pronounced is Fractional Flow Reserve (FFR), which is defined as the ratio of hyperemic flow in the stenosis artery to the flow in the same artery in the theoretic absence of the stenosis [2]. FFR is lesion specific and provides functional assessment of the stenosis severity by means of pressure measurement as a surrogate for flow. Under hyperemic flow conditions, FFR can be calculated as the ratio of pressures distal and proximal to a lesion. FFR values of 0.75–0.80 have been established as threshold values that distinguish normal from abnormal levels for a given measurement. Stenoses with an FFR < 0.75 are considered as a cause of myocardial ischemia, whereas stenoses with an FFR > 0.80 are considered to be ischemic ‘safe’ [2]. One of the limitations of FFR is its absolute dependency in pharmacologically-induced maximal hyperemia. The current clinical standard for coronary hyperemia is the intracoronary administration of ademosine, however in 10% to 15% of patients, intracoronary adenosine induces submaximal hyperemia only, and therefore FFR may be overestimated by up to 0.10 [3, 4].