A stress test with myocardial perfusion is an imaging procedure that evaluates blood flow to the heart muscle. Often called a nuclear stress test, it uses a small amount of radioactive material to create heart images. This diagnostic tool assesses how well the heart muscle receives blood, both at rest and during physical exertion or simulated stress.
Purpose of the Test
The test primarily detects and assesses coronary artery disease (CAD), which involves the narrowing or blockage of arteries supplying blood to the heart muscle. It identifies if parts of the heart muscle are not receiving enough blood flow, especially when the heart is working harder.
The test can also determine the extent of heart muscle damage after a heart attack. Its findings guide treatment decisions, helping determine the need for further interventions or adjustments to a patient’s management plan.
How the Test is Performed
The stress test with myocardial perfusion involves two primary components: inducing stress and capturing images of the heart. The stress component can be achieved through either physical exercise or medication. For exercise stress, individuals typically walk on a treadmill or pedal a stationary bike, with the intensity gradually increasing. During this phase, heart rate, blood pressure, and electrical activity of the heart (ECG) are continuously monitored.
If a person cannot exercise adequately, medication is used to simulate the effects of physical stress. These pharmacological agents, such as adenosine, dipyridamole, or regadenoson, widen the heart’s blood vessels, mimicking the increased blood flow that occurs during exertion. Dobutamine is another option, which increases heart rate and contractility.
During both stress methods, a small amount of a radioactive tracer, commonly technetium-99m sestamibi, is injected into the bloodstream. This tracer travels to the heart muscle, and its uptake is proportional to the blood flow in different areas. Special cameras, such as SPECT (Single-Photon Emission Computed Tomography) or PET (Positron Emission Tomography), then detect the radiation emitted by the tracer.
Two sets of images are taken: one at rest and another immediately after the stress phase. Comparing these images identifies areas where blood flow is reduced only during stress (a potential blockage) or consistently reduced (damaged heart muscle). The imaging involves lying still on a table while the camera rotates around the body, usually taking about 15 minutes per set.
Preparing for Your Stress Test
Proper preparation ensures accurate test results and a smooth experience. Patients must fast for 4 to 6 hours before the test. Avoid caffeine for 12 to 24 hours, including coffee, tea, chocolate, sodas, and some over-the-counter medications; check labels.
Adjustments to regular medications may be necessary, and patients should discuss this with their doctor beforehand. Some heart medications, such as beta-blockers or calcium channel blockers, or nitrates, might need to be paused. Diabetic patients should consult their physician regarding insulin doses. Wearing comfortable, loose-fitting clothing and walking shoes is advisable, especially if an exercise stress test is planned.
Interpreting Your Results
The myocardial perfusion scan images visually represent blood flow within the heart muscle. A normal result shows uniform radioactive tracer distribution across all heart areas in both rest and stress images, indicating healthy blood flow.
Abnormal results appear as “cold spots” or areas with reduced tracer uptake. If reduced uptake appears only in stress images but normalizes in rest images, it’s a “reversible defect,” suggesting a blockage limiting blood flow only under increased demand. A “fixed defect,” with reduced uptake in both rest and stress images, indicates damaged heart muscle from a previous heart attack or scar tissue. These findings guide decisions about further diagnostic procedures or treatment strategies.