Masked Ischemia on Myocardial Perfusion Imaging: A Case Example

Electrocardiography (ECG)-gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) for the diagnosis and prognosis of coronary artery disease (CAD) is the most commonly performed imaging procedure in nuclear cardiology.. A 67-year-old man underwent exercise electrocardiography (ECG)-gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) for evaluating his mild dyspnea on exertion (New York Heart Association class I). Images showed inducible ischemia of severe intensity in the interior walls and moderate intensity in the apicoseptal and anteroseptal segments, but exercise stress to induce coronary hyperemia revealed marked ST-segment depressions in low heart rates and the patient complained of only mild dyspnea during these ECG changes. He subsequently underwent coronary angiography, which revealed left main and severe three-vessel disease. This discrepancy between the SPECT perfusion images and the extent of coronary artery disease in this case represents the masking of one ischemic territory (left system) by another more severely ischemic territory (right system).. The reason is that we assess the relative and not absolute differences of the tracer uptake in this imaging modality. There may be other findings on MPI images which could help us overcome this pitfall, including detecting wall motion abnormalities, lung uptake of the tracer, or transient ischemic dilation. Another important issue is the ECG changes during exercise stress testing, which could point to a more extensive coronary artery disease than the one detected on MPI images alone..