MPI is a non-invasive nuclear medicine technique that is used to evaluate the viability, as well as the blood supply to, the heart muscle.

Examination

The conventional procedure is done in two stages over two different days.  During each of these visits a small amount of radio-isotope tracer is injected in the arm.  The activity of the tracer in the heart is picked up by a gamma camera.  During one of these visits the heart is stimulated by an infusion of “adenosine” that stresses the heart, and so induces lack of blood supply (angina).  The other visit is conducted with the patient at rest.  The information gained during these two scans is then analysed to evaluate the blood supply to the heart.

Benefits

• MPI is more sensitive as compared to a conventional treadmill exercise test in detecting lack of blood supply to the heart muscle (90% vs. 65%).
• Is of particular advantage for women, for people who have certain unusual patterns in the electrical activity of their heart (these patterns are detected by ECG), people with diabetes or people for whom exercise is difficult or impossible
• Can localise the exact area of lack of blood supply to the heart that corresponds to the different coronary vessels.
• Is able to differentiate living muscle as compared to scars after a heart attack.
• Provides additional useful details about the functioning of the heart.
• Is a valuable tool to identify the presence of coronary disease in asymptomatic patients.
• Very useful to stratify the cardiac risk prior to any form of anaesthesia.
  

Risks

• The investigation involves radiation exposure from the administration of a very small dose of radioactive tracer.
• During administration of Adenosine some patients may feel side effects like flushing and chest tightness that subside immediately after discontinuing the drug.
• For pregnant women, the risks and benefits of undergoing nuclear scanning should be assessed.