Nuclear Myocardial Perfusion Assessment

SPECT imaging, most commonly using ^99m Tc-labeled compounds (sestamibi or tetrofosmin), or PET imaging (⁸² Rb or ¹³ N-ammonia), obtained at peak stress and at rest, depicts zones of prior infarction as fixed defects and regions of inducible myocardial ischemia as reversible defects. Nuclear imaging is more sensitive, but less specific, than stress echocardiography for detection of ischemia. Left ventricular contractile function can also be assessed during SPECT imaging.

For pts who cannot exercise, pharmacologic perfusion imaging with adenosine, regadenoson, dipyridamole, or dobutamine is used instead (Chap. 123 Chronic Stable Angina). For pts with LBBB, perfusion imaging with adenosine or dipyridamole is preferred to avoid artifactual septal defects that are common with exercise imaging.

Pharmacologic PET scanning is especially useful in imaging obese pts and to assess myocardial viability (Thallium-201 SPECT imaging can assess viability when PET is not available). PET metabolic imaging is helpful in defining regions of myocardial inflammation and response to therapy in cardiac sarcoidosis.