The noninvasive assessment of myocardial viability

Abstract

Summary:The major objective of noninvasive imaging for detection of myocardial viability is to assist in the improved selection of patients with coronary artery disease and severe left ventricular dysfunction who would benefit most from revascularization. The techniques most commonly used to identify viable myocardium are thallium-20 I ('O'TI) scintigaphy, positron emission tomography (PET) using a flow tracer in combination with a metabolic tracer, technetium-99m (wmTc) sestamibi imaging, and dobutamine echocardiography. On stress ?"IT1 scintigraphy, asynergic regions showing normal thallium uptake, an initial defect with delayed redistribution at 3-4 h, late redistribution at 24 h, or defect reversibility after reinjection of a second dose of 'OITI at rest all suggest preserved viability. The greater the final uptake of 201Tl in areas of regional myocardial dysfunction preoperatively, the greater the improvement in ejection fraction after coronary revascularization. Demonstration of uptake of fluoro-I8 deoxyglucose (FDG) in regions of diminished blood flow on PET imaging also correlates well with improved systolic function after revascularization. 9 9 m T~ sestamibi may also be useful for assessment of myocardial viability, particularly after thrombolytic therapy for acute myocardial infarction. Dobutamine echocardiography has good positive predictive value for viability determination, but absence of systolic thickening in an akinetic zone in response to intravenous infusion of the drug may still be associated with viable myocardium in 25-50% of segments. Of all the techniques cited above, quantitative resting zO'TI scintigraphy may be the best approach for distinguishing between viable and irreversibly injured myocardium.

Imaging of myocardial perfusion with magnetic resonance

“…With Thallium‐201 or TC‐99m sestamibi SPECT, the signal intensity in the myocardium depends on the myocardial blood flow and the amount of viable cells extracting the tracer into the intracellular space. Therefore, areas with decreased myocardial perfusion as well as areas with a reduced number of viable cells result in reduced tracer uptake (8, 10). In contrast, the myocardial signal intensity on MR images during first‐pass perfusion of a paramagnetic contrast agent depends on myocardial blood flow, vascular permeability, and the size of the extracellular space.…”

Practical Implications of Myocardial Viability Studies

“…In fasting conditions, myocardium uses preferentially free fatty acids as energy source, whereas in post-prandial phase, its metabolism is shifted to glucose (with increased levels of circulating insulin). 5 As the metabolism of free fatty acids depends on oxygen, during myocardial ischemia, glucose is the preferred substrate (glycolytic pathway), which is the hallmark of myocardial viability. 35 , 32 - 35…”

“…Also, it may be helpful for surgeons and cardiologists in choosing the best therapy from interventionist strategy, angioplasty and myocardial revascularization. 5 This is particularly important in cases when myocardial revascularization is considered, due to high mortality rate and perioperative morbidity in these patients. 6 …”

An overview of contemporary nuclear cardiology

“…An alternate protocol that is gaining popularity is to give sublingual nitroglycerin prior to reinjection with 201 Tl [5]. From a practical standpoint, 201 Tl offers the advantage of use of a single injection of the isotope to demonstrate ischemia and to evaluate for hibernating but viable myocardium [6].…”