Myocardial blood flow and metabolism in humans

Segmental reductions in blood flow together with segmental shifts in substrate metabolism from oxidation of fatty acids to aerobic and anaerobic usage of glucose, commonly associated with regional myocardial ischemia in humans, can now be assessed noninvasively with position emission tomography (PET). Characterization of metabolic rather than blood flow changes is superior for assessing tissue viability. Persistence of metabolic activity, though abnormal, in myocardial segments with reduced blood flow and function as detected by PET is associated with greater morbidity in patients post myocardial infarction and identifies in chronic ischemic heart disease injured but viable myocardium that benefits from surgical revascularization. PET also detects persistent metabolic activity in acutely infarcted tissue and hence may guide interventions for salvaging injured myocardium.