Myocardial ischemia in patients with large prior infarction: Clinical decision making and review of literature

Myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) or positron emission tomography (PET) is a widely used technique for the evaluation of coronary artery disease (CAD). Interpreting physicians rely on regional variations in myocardial radiotracer uptake between rest and stress images to identify hemodynamically significant epicardial coronary artery stenosis. However, interpretation of MPI is very difficult in patients with large infarcts where there is no scintigraphically normal reference myocardium for comparison. In these patients, the stress and rest images appear similar due to balanced ischemia in the non-infarct territory. There are no clear guidelines on how to approach these cases. We present a case of MPI with a large right coronary artery territory (RCA) infarct where the left main (LM) coronary artery territory has no relative comparator and the images looked the same on stress and rest. However, the patient had multiple high-risk ancillary findings including electrocardiographic (ECG) changes with regadenoson, transient ischemic dilatation (TID), large severe inferior infarct, low myocardial blood flow (MBF) and myocardial flow reserve (MFR), but most notably increased right ventricular (RV) uptake on the stress images that was a subtle clue that we were dealing with LM equivalent in non-infarct zone. The coronary angiogram confirmed our findings. Through our case, we provide a comprehensive approach and review of literature on how to approach such challenging encounters.