[Isotopes and myocardial ischemia]

Single photon emission computed tomography (SPECT) is superior to conventional radionuclide scintigraphy. The most widely used marker is thallium-201, despite the fact that it is not exclusively flow-dependent. Thallium-201 SPECT can be performed in patients at rest, during exercise followed by a redistribution study, under dipyridamole or nitrate infusion, or combined with spasm provocation test. When performed at rest, it is helpful to diagnose and, above all, quantify a myocardial infarction. Under nitrate infusion, it delineates the viable muscle remaining around the infarct. During exercise or under dipyridamole infusion, it is more effective than any other non-invasive method in detecting myocardial ischaemia (sensitivity 95%, specificity 90%). Following surgical revascularization, a normal exercise SPECT indicates a functional aorto-coronary bypass in 80% of the cases. It is a good method to detect post-angioplasty restenosis (sensitivity 82%, specificity 86%, negative predictive value 93%). Like all paraclinical examinations, SPECT has its limitations: left bundle branch block, reverse redistribution, non-ischaemic (i.e. dilated or hypertrophic) cardiopathies.