Imaging of coronary flow capacity: is there a role for dynamic CT perfusion imaging?

Abstract

The assessment of myocardial ischaemia in patients with coronary artery disease (CAD) being considered for myocardial revascularization procedures is of paramount importance. The detection of a large area of myocardial ischaemia by functional imaging is associated with impaired prognosis of patients and identifies patients who should undergo revascularization [1]. Non-invasive functional evaluation of myocardial ischaemia should be the first approach and can be achieved with a variety of techniques. Nevertheless, invasive coronary pressure-derived fractional flow reserve (FFR) is the current standard of care for the functional assessment of angiographically intermediate-grade stenosis (typically around 40–90% stenosis) without evidence of ischaemia in non-invasive testing, or in those with multivessel disease. In the FAME 2 trial, percutaneous coronary intervention (PCI), as compared to medical therapy, was associated with lower incidence of the primary composite endpoint of death, myocardial infarction, and urgent revascularization in patients with stable CAD and at least one stenosis with FFR ≤0.80 [2]. Recently, two large-scale randomized trials showed broadly comparable results between FFR-guided and the resting index instantaneous wave-free ratio (iwFR)-guided revascularization strategies in patients with intermediate-grade stenosis [3, 4]. Myocardial blood flow and coronary flow reserve (CFR, i.e. the ratio between hyperemic to rest flow) are the critical determinants of myocardial ischaemia. Invasive pressurederived FFR, originally validated by comparison to stress positron emission tomography (PET), is the derivative approximation of the relative regional distribution of stress perfusion expressed as a fraction of maximum stress perfusion in ml/ min/g [5]. Coronary flow capacity (CFC), originally developed using PET, integrates the simultaneous regional size severity of resting myocardial blood flow (MBF), hyperemic MBF, and CFR [6]. CFCmaps provide specific patterns that are more accurate than CFR for distinguishing the effects of focal CAD, diffuse non-obstructive CAD and microvascular dysfunction by accounting for perfusion heterogeneity [7]. Severely reduced CFC, defined as the coexistence of stress MBF ≤0.91 ml/min/g and CFR ≤1.74, has been shown to predict a significant reduction in death or myocardial infarction after revascularization compared with medical treatment or less severe perfusion abnormalities [7]. In the current issue of the Journal, Bober et al. assessed the effects of coronary revascularization by percutaneous coronary intervention on stress MBF by PET [8]. Fifty patients, who underwent clinically indicated dipyridamole myocardial Rb PET, were enrolled in the study after coronary revascularization. A follow-up dipyridamole myocardial Rb PETwas performed within 90 days from coronary revascularization. For image analysis the left ventricle was divided into four quadrants corresponding to the distribution of the coronary arteries: anterior, septal, lateral and inferior [9]. Each quadrant was visually inspected for the presence of baseline significant relative perfusion abnormality (PA) defined as ≥10% change in size and/or severity from the resting scan. In addition, rest and stress MBF, CFR and CFC were calculated for each quadrant. Four different This article is part of the Topical Collection as an Editorial.