Assessment of intra-coronary pressure and flow velocity relations distal to coronary stenoses to derive a novel index of stenosis severity

Abstract

The optimal treatment for patients with stable angina remains controversial. Coronary angioplasty is increasingly performed in stable patients to reduce symptoms. Over the last 20 years there has been an accumulation of data demonstrating that an objective physiological approach to revasularisation is superior to the tradional angiographic approach. Several intra-coronary indices of stenosis severity have been proposed using pressure alone, flow velocity alone or a combination of both pressure and flow velocity. The most clinically used index, Fractional Flow Reserve (FFR) uses pressure alone to estimate the effect of a stenosis on blood flow within the coronary artery. Potent vasodilators are administered during its measurement to ensure the intra-coronary conditions are suitable for pressure to be used as a surrogate for flow. Despite the wealth of evidence supporting its use to guide coronary resvascularisation its adoption is poor. One reason is the need for the potent vasodilators that add time and cost to the procedure, cannot be given to every patient, are associated with side effects and in some regions of the world are simply unavailable. In this series of studies I will use combined pressure and flow velocity measurements to analyse the phasic relations of pressure and flow velocity distal to coronary stenoses. I aim to identify a period in the cardiac cycle that naturally provides the requisite intra-coronary condition for a pressure only index of stenosis severity - stable intra-coronary microvascular resistance. I will then compare the index derived over this period to existing pressure only and flow based indices of stenosis severity. Finally I will perform a detailed analysis of diastole to detemonstrate why this period is suitable by relating wave-mechanics to traditional pressure and flow mechanics.