Myocardial Perfusion Scintigraphy (MPS), also known as a myocardial perfusion scan, is a non-invasive imaging test used to assess heart health. This procedure uses a small amount of a radioactive tracer to investigate blood supply to the heart muscle. It provides a detailed look at how blood flows through the heart at rest and during stress, helping medical professionals understand the heart’s function.
What MPS Cardiology Assesses
An MPS scan evaluates blood flow to the heart muscle, known as the myocardium, and assesses its overall function. It helps diagnose conditions like coronary artery disease (CAD), where arteries supplying blood to the heart become narrowed or blocked.
The scan also assesses damage to the heart muscle following a heart attack, or myocardial infarction. By comparing blood flow at rest and during stress, MPS differentiates between reduced blood flow (ischemia) and damaged heart muscle (infarction or scar tissue). Ischemia indicates an area not receiving enough blood, especially under increased demand. Infarction signifies an area of muscle that has died due to prolonged lack of blood flow. This distinction guides treatment decisions and evaluates cardiac therapies.
The MPS Procedure
Preparing for an MPS scan involves specific instructions. Patients may be asked to fast for a few hours and adjust certain medications, especially those affecting heart rate or blood flow. Discuss all current medications with your healthcare provider before the scan.
During the procedure, a small amount of a radioactive tracer, such as Technetium-99m sestamibi or Thallium-201, is injected into a vein. This tracer travels through the bloodstream and is absorbed by the heart muscle in proportion to its blood flow. A gamma camera then detects the gamma rays emitted by the tracer, creating heart images.
The MPS procedure involves two main phases: rest imaging and stress imaging. For the rest phase, the tracer is injected while the patient is at rest, and images show baseline blood flow.
The stress phase evaluates blood flow when the heart works harder. Stress can be induced through exercise, like walking on a treadmill, or through pharmacological agents. For those unable to exercise, medications like adenosine, dipyridamole, or dobutamine mimic exercise effects, increasing heart blood flow. After stress induction and tracer injection, another set of images is taken.
Understanding Your Scan Results
Cardiologists interpret MPS scan images by analyzing radioactive tracer distribution within the heart muscle. In a normal result, tracer uptake appears uniform across all myocardium areas, indicating healthy and consistent blood flow at rest and during stress.
Abnormal results show areas of reduced or absent tracer uptake, called “perfusion defects.” A reversible defect indicates reduced uptake during stress but normal uptake at rest, suggesting ischemia. This means the heart muscle is not receiving enough blood flow under stress but recovers at rest. A fixed defect shows reduced tracer uptake both at rest and during stress, indicating an infarction or scar tissue from a previous heart attack. These findings provide insights into heart muscle damage or compromised blood flow, guiding treatment strategies.
Safety and Considerations for Patients
Patients often have concerns about radiation exposure during an MPS scan. The small amount of radioactive tracer used results in a radiation dose considered safe and comparable to other common diagnostic imaging tests. The benefits of obtaining detailed heart health information outweigh the minimal risks associated with this exposure.
While well-tolerated, some patients might experience mild side effects from the tracer or stress agents. These can include a temporary feeling of flushing, mild chest discomfort, or a headache, especially during the pharmacological stress portion of the test. These effects are transient and resolve quickly. Patients should inform their doctor about any allergies, current medications, and if they are pregnant or breastfeeding, as these factors influence the procedure and tracer choice.