Imaging modalities for detection of myocardial viability

Perfusion and metabolic tracers play an increasing role in the detection of viable, hibernating [1] and stunned myocardium [2]. These conditions are discussed, in more detail elsewhere but Table 1 summarises some of their properties and methods of detection. The term 'viable' strictly refers to myocardium which is alive, without implying any particular state of function, perfusion or metabolism. Normal myocardium could be described as viable, as could myocytes within an area of partial thickness infarction or myocardium that has been salvaged by thrombolysis but remains jeopardised by a coronary stenosis. Sometimes the term is used interchangeably with 'hibernation' although it is better to avoid this potentially confusing terminology. Using positron emission tomography, myocardium with impaired flow at rest and increased glucose metabolism may have improved function after coronary bypass grafting [3,4] or after angioplasty [5]. More importantly, revascularisation also reduces the risk of infarction and death in patients with impaired left ventricular function and hibernating myocardium demonstrated by positron emission tomography [6]. The mismatch of perfusion and glucose metabolism demonstrates that the myocardium is viable but underperfused and that it is metabolically embarrassed, having switched from normal aerobic fatty acid metabolism to glucose metabolism. It is important, however, to specify the conditions under which FDG studies are performed. Normal myocardium in the fasting state takes up very little FDG and only ischaemic myocardium is seen in the images by virtue of the change to glucose metabolism. In contrast, a glucose meal taken before imaging leads to significant uptake even in normal myocardium and FDG is act