ADVANCES IN FUNCTIONAL MYOCARDIAL VIABILITY IMAGING

Abstract

Revascularization improves prognosis of heart failure in patients of ischemic heart disease who have evidence of myocardial viability; therefore accurate assessment of myocardial viability remains essential. Viability assessment is based on different characteristics of the viable myocardium, which include cell membrane integrity, intact mitochondria, preserved glucose and fatty acid metabolism, intact perfusion during rest and stress and contractile reserve. Current clinical imaging modalities, including those used in myocardial viability assessment, are usually classified into anatomical and functional imaging modalities and techniques , where anatomical imaging is mainly focused on structural changes, while functional imaging aim at providing the functional aspects at cellular or molecular level. The viable hibernating myocardium is characterized on imaging by preserved myocyte membrane integrity and metabolism, contractile reserve during stimulation and absence of scar. In contrast, absence of contractile reserve, identification of scar, loss of membrane integrity or metabolic activity can be used to define the non-viable tissue. Membrane integrity can be assessed by uptake of thallium-201(201 Tl) or 99-m technetium tracers, metabolism by uptake of 18F-Fluorodeoxyglucose (18F–FDG), presence of contractile reserve by stress imaging, e.g. Stress Cardiac Magnetic Resonance (CMR) imaging, and presence of scar by Late Gadolinium Enhancement (LGE) on CMR. Multiple other complimentary imaging techniques can also be used to identify the viable myocardium.