What is a Spect MPI (Myocardial Perfusion Imaging)?

From the Guidelines

SPECT MPI is a highly recommended diagnostic tool for evaluating coronary artery disease, particularly in patients with chest pain and a high likelihood of CAD, as it provides valuable information on myocardial perfusion and ischemia, with a sensitivity of 78% and specificity of 52% for detecting significant CAD and/or myocardial ischemia 1.

Key Points

• SPECT MPI is a non-invasive procedure that evaluates blood flow to the heart muscle during rest and stress, using a radioactive tracer such as technetium-99m sestamibi or thallium-201.
• The test involves two sets of images, one taken after stress and another at rest, to identify areas with reduced blood flow, which may indicate potential blockages in coronary arteries.
• SPECT MPI is particularly useful for patients with chest pain, known coronary artery disease, or those with risk factors for heart disease, as it helps diagnose coronary artery disease and predicts the likelihood of cardiac death or nonfatal myocardial infarction.
• A normal stress SPECT MPI examination in patients with an intermediate to high likelihood of CAD predicts a low rate of cardiac death or nonfatal myocardial infarction (1% per year) 1.

Clinical Applications

• SPECT MPI is useful for estimating the extent and severity of coronary stenosis, which has relevance for prognosis, choice among therapeutic options, and advisability of performing coronary arteriography.
• The test can identify inducible ischemia, which predicts short-term benefit from revascularization, while left ventricular ejection fraction (LVEF) predicts cardiac death 1.
• SPECT MPI can be used for risk stratification in scenarios such as follow-up after percutaneous coronary intervention (PCI) and coronary artery bypass graft or evaluation before noncardiac surgery.

Limitations and Future Directions

• SPECT MPI has relatively high cost and radiation dose, but software algorithms and new hardware and detector materials are being developed to refine image acquisitions and reduce radiation exposure 1.
• Hybrid SPECT/coronary CT angiography (CCTA) combines anatomic information from CT with functional perfusion evidence from SPECT, resulting in enhanced diagnostic accuracy for detecting significant CAD compared to SPECT and CCTA alone 1.

From the Research

Spect MPI

• Spect MPI is a mainstay of nuclear cardiology for the detection of myocardial ischemia, employing technetium-99m (Tc-99m)-based imaging tracers 2.
• Current guidelines for same day rest/stress Tc-99m-sestamibi SPECT MPI recommend image acquisition 15-60 minutes after the stress testing 2.
• A novel sensitive SPECT imaging technique, D-SPECT, allows fast acquisition of images and captures rapid changes in radiotracer distribution, which may facilitate the detection of coronary artery disease (CAD) 2.
• The synergistic use of coronary artery calcium (CAC) scanning and stress-rest SPECT MPI can improve the diagnostic sensitivity and predictive value of cardiac risk 3.
• CAC scanning can identify normal SPECT-MPI patients with subclinical atherosclerosis and improve the interpretation of borderline SPECT-MPI scan abnormalities 3.

Diagnostic Pathway

• The integration of anatomic and functional information from SPECT and CAC can provide additional information for the clinician by improved risk stratification and diagnostic accuracy 4, 5.
• Patients at low risk for CAD can be selected for primary prevention, and patients at high risk for CAD can be directly selected for coronary angiography (CAG) 5.
• The remaining group of patients at intermediate risk for CAD can be substratified into lower- and higher-risk categories based on the presence or absence of stress-induced ischemia on MPI SPECT and CAC scoring 5.

Predictors of High-Risk CAD

• Several clinical, stress, and SPECT-MPI findings are associated with high-risk CAD among patients with normal SPECT-MPI, including pretest probability of CAD ≥66%, SSS > 0, and abnormal TID 6.
• The prevalence of high-risk CAD increases as the number of these predictors increases 6.
• Quantitative total perfusion deficit (TPD) > 0 is also a predictor of high-risk CAD in patients with normal SPECT-MPI 6.