A nuclear medicine stress test, also known as a myocardial perfusion scan, is an imaging procedure that evaluates the heart’s function and blood flow. It uses a small amount of a radioactive substance, called a tracer or radionuclide, to create images of the heart. This diagnostic tool assesses how blood moves through the heart’s arteries at rest and during physical exertion or simulated stress, providing information about the heart’s blood supply.
Diagnostic Insights
The test identifies and assesses potential blockages within the coronary arteries, which are the major blood vessels supplying the heart. By comparing images taken at rest and under stress, healthcare providers can detect areas of reduced blood flow. This indicates conditions like coronary artery disease (CAD) or myocardial ischemia, which occurs when the heart muscle does not receive enough blood.
A nuclear stress test determines the severity of CAD and assesses the effectiveness of previous cardiac interventions, such as bypass surgery or stenting. It can show if there is damage from a prior heart attack or if a person needs further procedures like a coronary angiogram. The test provides insights into the heart’s overall pumping ability and its capacity to handle physical activity.
The Test Procedure
Preparation for a nuclear medicine stress test involves avoiding caffeine for at least 12 to 24 hours beforehand, which includes coffee, tea, soft drinks, and chocolate. Patients are instructed not to eat or smoke for a few hours prior to the test, though water is permitted. Wear comfortable clothing and athletic shoes, especially if an exercise component is planned. Patients should inform their healthcare provider about all medications they are taking, as some may need to be adjusted or temporarily stopped before the test.
The procedure begins with the patient at rest, where an intravenous (IV) line is inserted into a vein, typically in the arm or hand. A small amount of a radioactive tracer is injected through this IV. After allowing 15 to 45 minutes for the tracer to circulate and be absorbed by the heart muscle, a special imaging machine called a gamma camera takes the first set of pictures of the heart. These “rest” images take 3 to 5 minutes to acquire.
Following the resting images, the stress phase of the test begins. If the patient is able to exercise, they will walk on a treadmill or pedal a stationary bike, gradually increasing the intensity. During peak exercise, a second dose of the radioactive tracer is injected. If a patient cannot exercise due to physical limitations or other medical reasons, a medication (pharmacological agent) is administered through the IV to simulate the effects of exercise on the heart, such as widening the heart arteries or increasing heart rate. After the stress phase, a second set of images is taken with the gamma camera, providing a view of blood flow to the heart under stress. The entire test can take two to four hours.
Patient Considerations and Interpreting Findings
The radioactive tracer used in a nuclear stress test exposes the patient to a small amount of radiation, considered safe. The radiation exposure from the test is comparable to other diagnostic imaging procedures like a CT scan. The tracer naturally decays and is eliminated from the body, primarily through urine and stool, within a day or two. Patients are advised to drink plenty of fluids after the test to help flush the tracer out of their system.
While well-tolerated, some temporary side effects can occur during or after the test. Patients might experience mild nausea, headache, dizziness, or fatigue. If a pharmacological stress agent is used, some individuals may feel a warm sensation or a racing heart. Rarely, more significant issues like irregular heartbeats (arrhythmias) or a drop in blood pressure can occur, but these resolve quickly. Serious complications, such as a heart attack, are rare.
After the images are acquired, a cardiologist or radiologist compares the resting and stress images to interpret the findings. A normal test result indicates even blood flow to the heart muscle both at rest and during stress, suggesting no significant blockages. If there is normal blood flow at rest but reduced flow during stress, it suggests a temporary drop in blood supply due to a blockage in a coronary artery that becomes apparent when the heart’s demand for blood increases. If both resting and stress images show an area of poor blood flow, it may indicate permanent damage to the heart muscle, often from a previous heart attack. The healthcare provider will discuss these findings and determine any necessary follow-up care or treatment.