Myocardial perfusion imaging

Myocardial perfusion imaging
Intervention
Nuclear medicine myocardial perfusion scan with Thallium-201 for the rest images (bottom rows) and Tc-Sestamibi for the stress images (top rows). The nuclear medicine myocardial perfusion scan plays a pivotal role in the noninvasive evaluation of coronary artery disease. The study not only identifies some patients who have coronary artery disease, it can also provide overall prognostic information or overall risk of adverse cardiac events for the patient, provided that the patient does not suffer from Three-Vessel disease, the most serious result of coronary artery disease.
ICD-10-PCS	C22G
MeSH
OPS-301 code:	3-704, 3-721

Myocardial perfusion scan (also referred to as MPI) is a nuclear medicine procedure that illustrates the function of the heart muscle (myocardium).^[1]

It evaluates many heart conditions such as coronary artery disease (CAD),^[2] hypertrophic cardiomyopathy and heart wall motion abnormalities. The function of the myocardium is also evaluated by calculating the left ventricular ejection fraction (LVEF) of the heart. This scan is done in conjunction with a cardiac stress test.

Planar techniques, such as conventional scintigraphy, are rarely used. Rather, SPECT is more common in the US. With multihead SPECT systems, imaging can often be completed in less than 10 minutes. With SPECT, interior and posterior abnormalities and small areas of infarction can be identified, as well as the occluded blood vessels and the mass of infarcted and viable myocardium.^[3]

Major indications for a myocardial perfusion test

• Diagnosis of CAD and various cardiac abnormalities.
• Identifying location and degree of CAD in patients with a history of CAD.
• Prognosis of patients who are at risk of having a myocardial or coronary incident (i.e. myocardial infarction, myocardial ischemia, coronary aneurysm, wall motion abnormalities).
• Assessment of viable myocardium in particular coronary artery territory following heart attacks to justify revascularization
• Post intervention revascularization (coronary artery bypass graft, angioplasty) evaluation of heart.

Risks vs. benefits

Experimental and epidemiologic evidence has linked exposure to low-dose ionizing radiation with up to 2% of solid cancers and leukemia. Workers are monitored and limited to 100mSv every 5 years, but medical patients are not typically monitored.

From 1993-2001, myocardial perfusion scans increased >6%/y with "no justification," according to a commentary by Lauer. Mycardial perfusion imaging scans are "powerful predictors of future clinical events," and in theory may identify patients for whom aggressive therapies should improve outcome. But this is "only a hypothesis, not a proof," wrote Lauer. There are no randomized, controlled trials to demonstrate any benefits, and there is a small but cumulative danger from radiation.^[4]

New radionuclides such as rubidium-82 reduce the radiation dose to the patient by a factor of 10 compared to technetium-99m. In the future, therefore, a complete myocardial perfusion exam may be achievable while maintaining a patient dose under 3 mSv.^[5][6] Stress-only protocols may also prove to be effective at reducing costs and patient exposure.^[7]

References