Stress/Rest Myocardial Perfusion Imaging (MPI)

A Stress/Rest Myocardial Perfusion Imaging (MPI) Study is a type of stress test that uses PET or SPECT imaging of a patient’s heart before and after exercise to determine the effect of physical stress on the flow of blood through the coronary arteries and the heart muscle.

The three-dimensional images produced by this study are called perfusion images because they show which areas of the heart muscle are perfused, or supplied, with blood.

The stress/rest MPI may also be referred to as a cardiac or nuclear stress test, a thallium scan or a sestamibi cardiac scan.

A physician may perform a Stress/Rest MPI study to:

• assess the overall function of the heart muscle heart and the function of individual muscle walls
• assess damage to the heart muscle following a heart attack
• diagnose symptoms of coronary artery disease(CAD), such as shortness of breath or chest pain. Abnormal perfusion scans are highly indicative of CAD
• determine the extent of coronary stenosis, a narrowing of arteries that supply blood to the heart
• determine whether a patient is a candidate for revascularization, a surgical procedure that restores blood flow
• manage the treatment of coronary artery disease by evaluating the results of:
  • revascularization procedures
  • medical or drug therapy.

How is a Stress/Rest MPI Study Performed?

For the exercise portion of the test, the patient is asked to walk or run on a treadmill in order to elevate the heart to its peak rate. Patients who are unable to exercise are given a drug that elevates the heart rate (called a pharmacologically induced stress test). The patient’s heart rate and blood pressure are monitored during this phase of the test.

The patient then receives an intravenous injection of  a radiotracer called thallium, which accumulates in the heart muscle. Next, the patient is moved to an imaging suite, where images of the heart are taken with a SPECT camera or PET scanner. Several hours later, the patient is imaged again.

Alternatively, a radiotracer called sestamibi may be used. This radiotracer requires two injections for the exercise or stress portion of the study and later for the resting portion of the study, which may be scheduled a day ahead or after the stress test.

Who Benefits from Stress/Rest MPI Studies?

For some patients at low-risk for heart disease, a stress test using echocardiography, known as an ECG stress test or exercise treadmill testing, alone is frequently sufficient. However, in patients with a moderate-to-high risk for coronary artery disease, an MPI study is essential in addition to a stress test. Patients who have an abnormal exercise stress test will usually require additional stress testing, such as a Stress/Rest MPI study and/or coronary angiography.

Physicians ensure the Stress/Rest MPI Study is appropriate for patients by:

• carefully evaluating each patient’s clinical characteristics, coronary artery disease (CAD) risk factors, prior history of CAD and heart (specifically left ventricular) function.
• applying Appropriate Use Criteria (AUC) and guidelines developed and endorsed by SNM, the American Society of Nuclear Cardiology and other professional societies based on a large body of scientific evidence including studies on thousands of patients.
• using the ALARA principle (As Low As Reasonably Achievable) to carefully select the amount of radiopharmaceutical that will provide an accurate test with the least amount of radiation exposure to the patient.

Advantages of Stress/Rest MPI

This study is:

• is the most accurate test available for diagnosing coronary artery disease (CAD) early in patients who may be at risk for a heart attack
• has a proven risk-stratification capability: abnormal perfusion scans are highly indicative of coronary artery disease (CAD). Research has also shown that patients with normal MPI scans have less than a one percent risk of heart attack or cardiac death for up to five years
• is sensitive to even the most modest changes in blood flow to the heart
• offers improved diagnostic accuracy over exercise treadmill testing (also called an ECG stress test).