Effectiveness of fractional flow reserve and resting full-cycle ratio in arteries with tandem stenosis

Coronary artery disease, associated with significant mortality and morbidity, is caused by atherosclerotic stenoses (blood vessel cholesterol blockages) obstructing coronary blood flow. Stenoses may be widespread, with several occurring in one coronary artery. Where multiple stenoses occur in the same coronary artery, the degree to which the stenoses affect each other is not necessarily well understood. This research aims to investigate the pressure behaviour across pairs of stenoses using a purpose-built coronary flow rig. Additionally, for the first time, the effect of an additional stenosis on measurements of fractional flow reserve (FFR), resting full-cycle ratio (RFR), instantaneous wave free ratio (iFR) and hyperaemic stenosis resistance (hSR) were compared in a controlled environment. Results demonstrate that having a secondary, less severe, stenosis downstream can lessen the overall pressure drop and cause a pressure increase across the second stenosis. The effect of the second stenosis appears to be negligible as the separation increases. All indices are altered by the presence of an additional stenosis. However, FFR, RFR and hSR all display similar behaviour, whereas hSR appears to be more greatly altered, when compared with a single equivalent stenosis. Finally, the pressure behaviour is used to propose a separation range, beyond which the two stenoses should be treated as separate blockages. Findings suggest that the presence of a second stenosis alters the flow and pressure behaviour in a stenosed vessel, and may even be of potential benefit in some cases, although further research is required.