What Is a PET Scan Stress Test Explained
A Positron Emission Tomography (PET) scan stress test is a specialized diagnostic imaging procedure used to evaluate heart health. It combines a PET scan, which visualizes metabolic activity and blood flow, with a stress test, assessing the heart’s response to increased demand. This combined approach offers detailed insights into how well blood flows to the heart muscle, both at rest and during exertion.
The Test Explained
A PET scan uses a small amount of radioactive tracer injected into the bloodstream. This tracer emits positrons, detected by the PET scanner to create detailed images of organs and tissues. For cardiac PET scans, the tracer measures blood flow to the heart muscle, providing information about its perfusion and metabolic activity.
The stress test component increases the heart’s workload to observe its response under demand. This is achieved through physical exercise, such as walking on a treadmill or cycling. For those unable to exercise, medication is administered intravenously to mimic exercise effects on the heart.
By combining these two elements, the PET scan stress test provides a comprehensive assessment. The tracer is administered twice: once at rest, and again immediately after the heart has been stressed. Comparing the images obtained during rest and stress allows physicians to identify differences in blood flow or metabolic activity in various regions of the heart muscle. This comparison reveals the heart’s ability to receive adequate blood supply under varying conditions.
Why This Test is Performed
The PET scan stress test assesses blood flow to the heart muscle, a process known as myocardial perfusion. It identifies areas of ischemia (insufficient blood flow) or infarct (damaged heart tissue, often from a prior heart attack). The test helps distinguish between these two conditions, which is important for guiding treatment.
This diagnostic tool diagnoses coronary artery disease (CAD), a condition where heart arteries narrow or block. It also evaluates the severity of known CAD and its impact on heart function. Physicians may order this test to assess if revascularization procedures, such as bypass surgery or angioplasty, would be beneficial.
Beyond diagnosis, it evaluates symptoms like unexplained chest pain, shortness of breath, or unusual fatigue, particularly when other tests are inconclusive. It also assesses heart muscle viability after a heart attack, indicating whether damaged tissue can recover with improved blood flow.
The Procedure Steps
Before undergoing a PET scan stress test, patients receive specific instructions. This includes fasting for several hours (typically four to six) and avoiding caffeine or certain medications for a day or two beforehand. These preparations help prevent interference with the tracer or stress agents.
Upon arrival at the imaging center, an intravenous (IV) line is inserted, usually in an arm vein, for administering the tracer and stress medications. Electrodes are placed on the chest to monitor heart activity via an electrocardiogram (ECG).
The resting phase begins with an initial dose of the tracer injected through the IV line. After a 15-45 minute waiting period for the tracer to circulate, the patient lies on a scanning bed that slides into the PET scanner. This resting scan takes about 15-20 minutes to capture baseline images.
Following the resting scan, the stress phase begins. If physical exercise is used, the patient walks on a treadmill or pedals a stationary bike, gradually increasing intensity until a target heart rate is achieved or symptoms occur. If a pharmacologic stress agent (e.g., regadenoson or dobutamine) is administered, it is infused through the IV line, causing the heart to respond as if exercising. Throughout this phase, blood pressure, heart rate, and ECG are continuously monitored for safety.
Immediately after adequate stress, a second dose of the tracer is injected. The patient then returns to the PET scanner for stress images, captured while the heart is still under the effects of exertion or medication. This second scan is crucial for comparing blood flow under stress to the resting state. After both scans are complete, the IV line is removed, and the patient may be monitored briefly before discharge.
Interpreting the Findings
After the PET scan stress test, physicians analyze the images by comparing resting and stress images. This comparison identifies differences in blood flow or metabolic activity within heart muscle regions. Images are often displayed in cross-sectional views, enabling assessment of all heart segments.
A normal result shows uniform tracer distribution throughout the heart muscle during both rest and stress phases. This indicates all heart areas receive adequate blood supply, even when working harder. Such findings suggest healthy blood flow and no significant blockages in the coronary arteries.
Abnormal findings reveal areas of reduced blood flow. If an area shows reduced blood flow during stress but normal flow at rest, it suggests myocardial ischemia, indicating a blockage that limits blood supply only when heart demand increases. Conversely, persistently reduced or absent blood flow during both rest and stress indicates an infarct or scar tissue, where heart muscle is permanently damaged, often from a past heart attack.