Clinical Cardiac Positron Emission Tomography

Abstract

Randomized trials comparing medical management with coronary revascularization based on the coronary arteriogram show no reduction in the incidence of adverse events in patients with coronary artery disease (CAD). Other randomized trials report better outcomes after revascularization based on physiologic severity of coronary artery stenosis by fractional flow reserve (FFR) compared to revascularization based on the angiogram. This paradoxical outcome between angiographic and physiologic guided revascularization reveals a profound flaw in percent stenosis for assessing severity of CAD for and its management - percent stenosis is poorly related to FFR or coronary flow reserve capacity. This paradox suggests that failure of revascularization trials may be due in part to inappropriate patient selection based on the angiogram. Positron emission tomography (PET) quantifies the physiologic severity of CAD by high quality quantitative myocardial perfusion imaging as documented by a large evidence base over the past 25 years. Myocardial perfusion after pharmacologic stress in cc/min/gm and coronary flow reserve (CFR), define the precise low flow ischemic threshold causing angina and significant ischemic ECG changes suitable for revascularization, the severity of less severe and diffuse disease better treated medically. While invasive pressure derived FFR has had a profound influence toward physiologically guided revascularization, it has limitations. It is invasive and impacted by the per procedure reimbursement system. Left ventricular function and ischemia are determined more by coronary flow than pressure. Finally, a substantial number of patients show discordance between low FFR with adequate coronary flow reserve well above ischemic threshold. For such patients, medical treatment may be better than revascularization, an issue needing randomized trial. With appropriate clinical and technical expertise, myocardial perfusion imaging by PET can play the dominant role for managing CAD and guiding revascularization procedures as illustrated in this chapter.