What is a Nuclear Stress Test?
A Nuclear Cardiac Stress Test, also called Myocardial Perfusion Imaging (MPI), is a test that shows how well blood flows to your heart muscle. It uses a small, safe amount of a radioactive substance (a "tracer") and a special "gamma camera" to create pictures of your heart.
The key to this test is comparison. By comparing pictures of your heart at rest versus under stress, doctors can find areas of the heart that aren't getting enough blood, which is a clear sign of coronary artery disease (CAD).
Part 1: Rest Scan
Part 2: Stress Scan
The Process: A Two-Part Examination
Preparation
- You will be asked to fast (not eat) for at least four hours before the test.
- You must avoid all caffeine (coffee, tea, soda, chocolate) and nicotine for 24 hours.
- Your doctor will tell you which medications to stop or continue.
- Wear comfortable clothes and walking shoes for the exercise portion.
The Procedure
- Part 1 (Rest Scan): You'll get an IV, and a small amount of tracer is injected. After waiting 30-60 minutes for it to circulate, you'll lie under the gamma camera for the first set of images.
- Part 2 (Stress Scan): Your heart will be "stressed," either by exercising on a treadmill or with a medication (if you can't exercise). At peak stress, you'll receive a second tracer injection, followed by the second set of images.
Why Is This Test Needed?
- To Diagnose Coronary Artery Disease (CAD): This is the most common reason. It accurately finds blockages restricting blood flow.
- To Find the Cause of Chest Pain: It shows if symptoms like angina or shortness of breath are from a heart blockage.
- To Assess Heart Attack Damage: It can show the size of a scar from a previous heart attack.
- To Guide Treatment: The results help doctors decide if you need medications, an angioplasty (stent), or bypass surgery.
Rest
Stress
NORMAL
Rest
Stress
ISCHEMIA (Blockage)
Rest
Stress
INFARCT (Scar)
Understanding Your Results
1. Normal Result
This is great news. It shows that blood flow is uniform and sufficient to all parts of your heart, both at rest and under stress. This means you have no significant blockages.
2. Abnormal: Reversible Defect (Ischemia)
This is the most common abnormal finding. The images show an area of reduced blood flow during stress that looks normal at rest. This "reversibility" strongly suggests a blockage is preventing adequate blood flow when the heart works hard, but the muscle itself is still alive.
3. Abnormal: Fixed Defect (Infarction/Scar)
The images show a persistent "dark spot," or area of poor blood flow, on both the rest and stress scans. This indicates that a portion of the heart muscle has been permanently damaged and is now scar tissue, likely from a previous heart attack.
Treatment for Ischemia
Treatment for Scar Risk
How Doctors Provide Treatment
The treatment plan is based directly on your results.
- For a Normal Result: Your doctor will focus on managing risk factors (like blood pressure and cholesterol) with lifestyle changes and possibly medication.
- For a Reversible Defect (Ischemia): This indicates a blockage. Treatment will start with medications (statins, beta-blockers, aspirin) and lifestyle changes. If the blockage is large, your doctor will likely recommend a Coronary Angiogram to plan for a procedure like angioplasty (stenting) or bypass surgery.
- For a Fixed Defect (Scar Tissue): Treatment focuses on protecting the remaining healthy heart muscle with medications. Your doctor will likely order an Echocardiogram or Cardiac MRI to check your heart's overall pumping function (Ejection Fraction) and may recommend an ICD to prevent dangerous arrhythmias.