Myocardial Perfusion SPECT
Understand Myocardial Perfusion SPECT in Heart (coronary arteries and myocardium) SPECT imaging, what it means, and next steps.
30-Second Overview
Reversible perfusion defects indicate ischemia. Fixed defects suggest scar/infarction. Stress-induced ischemia shows reduced tracer uptake during stress with normalization at rest. Wall motion abnormalities and transient ischemic dilation may be present.
Myocardial perfusion SPECT (single photon emission computed tomography) is a cornerstone test for evaluating coronary artery disease. It provides functional assessment of blood flow to heart muscle, helping diagnose obstructive CAD, determine prognosis, and guide revascularization decisions. The test can detect ischemia at rest and during stress, distinguishing viable myocardium from scar tissue.
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Imaging Appearance
SPECT FindingReversible perfusion defects indicate ischemia. Fixed defects suggest scar/infarction. Stress-induced ischemia shows reduced tracer uptake during stress with normalization at rest. Wall motion abnormalities and transient ischemic dilation may be present.
Clinical Significance
Myocardial perfusion SPECT (single photon emission computed tomography) is a cornerstone test for evaluating coronary artery disease. It provides functional assessment of blood flow to heart muscle, helping diagnose obstructive CAD, determine prognosis, and guide revascularization decisions. The test can detect ischemia at rest and during stress, distinguishing viable myocardium from scar tissue.
Understanding Myocardial Perfusion SPECT
Myocardial perfusion imaging (MPI) with SPECT is a nuclear medicine technique that evaluates blood flow to the heart muscle at rest and during stress. The test uses radiotracers such as technetium-99m sestamibi, technetium-99m tetrofosmin, or thallium-201, which are taken up by myocardial cells in proportion to blood flow. By comparing stress and rest images, physicians can identify areas of ischemia (reversible defects) versus scar tissue (fixed defects).
Coronary artery disease develops when plaque builds up in the coronary arteries, restricting blood flow to the heart muscle. At rest, blood flow may be adequate, but during stress when the heart demands more oxygen, the narrowed arteries cannot deliver sufficient blood, creating a perfusion defect on SPECT imaging.
Reversible perfusion defects in a coronary artery distribution indicate inducible ischemia and high-risk CAD requiring urgent evaluation for revascularization
How the Test Works
The SPECT MPI study is typically performed as a two-day or one-day protocol:
Stress imaging: The patient exercises on a treadmill or receives pharmacologic stress (dipyridamole, adenosine, regadenoson, or dobutamine). At peak stress, the radiotracer is injected. Areas with reduced blood flow during stress show decreased tracer uptake.
Rest imaging: The patient returns for resting images, either several hours later (same-day protocol) or on a separate day. Resting images show the baseline blood flow pattern.
Image comparison: By comparing stress and rest images side-by-side, physicians can:
- Identify ischemia (reversible defect)
- Identify scar/infarction (fixed defect)
- Assess myocardial viability
- Determine the extent and severity of CAD
Accuracy highest when combined with clinical pre-test probability
Correctly rules out healthy patients
Annual new cases
Imaging Patterns
Reversible Perfusion Defects (Ischemia)
Ischemia shows as:
- Reduced tracer uptake on stress images
- Normal or improved uptake on rest images
- Follows coronary artery territory distribution
- May involve one or multiple vascular territories
Severity grading: Ischemia is categorized by extent and severity:
- Mild: Small defect, mild reduction in uptake
- Moderate: Medium-sized defect, moderate reduction
- Severe: Large defect or multiple territories, severely reduced uptake
Fixed Perfusion Defects (Scar)
Myocardial infarction/scar shows as:
- Persistently reduced tracer uptake on both stress and rest images
- No change between stress and rest
- Thin myocardium may be present
- Associated with wall motion abnormalities
Myocardial viability assessment: Some fixed defects may represent hibernating myocardium (stunned but viable). Viable tissue may benefit from revascularization.
Artifacts and Pitfalls
Common artifacts that can mimic disease:
- Breast attenuation (women): Reduced tracer uptake in anterior wall from breast tissue
- Diaphragmatic attenuation (men): Reduced inferior wall uptake from diaphragm
- Bundle branch block: Septal perfusion defect that may be artifactual
- Mediastinal uptake: Increased lung uptake may indicate pulmonary congestion or severe left ventricular dysfunction
Clinical Scenario
Normal Myocardial Perfusion
Uniform radiotracer uptake throughout left ventricular myocardium on both stress and rest images. No perfusion defects. Normal wall motion and thickening. Normal left ventricular ejection fraction (60-70%). No transient ischemic dilation.
Ischemic Heart Disease
Large reversible perfusion defect in the anterior and anteroseptal walls (LAD territory). Stress images show markedly reduced uptake in these regions, with partial normalization on rest images indicating ischemia with some scar. LVEF reduced to 45%. Mild transient ischemic dilation present.
Clinical Applications
Diagnostic Evaluation
Chest pain evaluation: MPI helps determine if chest pain is cardiac in origin. A normal MPI has a high negative predictive value, effectively ruling out obstructive CAD.
Known CAD assessment: For patients with known coronary disease, MPI determines the functional significance of stenoses seen on angiography and identifies the culprit lesion responsible for ischemia.
Risk Stratification
Prognostic information: MPI provides powerful risk stratification:
- Normal scan: ＜1% annual cardiac event rate (low risk)
- Mild ischemia: ~2% annual event rate (intermediate risk)
- Moderate/severe ischemia: ＞5% annual event rate (high risk)
Preoperative assessment: MPI evaluates cardiac risk before non-cardiac surgery, guiding perioperative management.
Treatment Guidance
Revascularization decisions: MPI helps determine:
- Which patients benefit from coronary angiography
- Which lesions are responsible for ischemia (need stenting or bypass)
- Whether medical therapy alone is sufficient
Post-revascularization: MPI assesses success of angioplasty or bypass surgery and detects restenosis or graft failure.
What Else Could It Be?
Reversible perfusion defect following coronary artery territory. Abnormal during stress, normal at rest. Correlates with angina symptoms. May show wall motion abnormality.
Fixed perfusion defect (same abnormality on stress and rest). Thin myocardium. History of infarction or elevated cardiac enzymes. No reversibility.
Diffuse relatively uniform reduction in tracer throughout all territories. May appear 'normal' due to balanced disease. Clinical suspicion high with negative scan.
Fixed defect in characteristic location (anterior in women, inferior in men). Normal wall motion and thickening on gated SPECT. No corresponding wall abnormality on echocardiogram.
Evidence-Based Outcomes
Preparing for Your Scan
Before the Appointment
- Fasting: No food or drink for 4-6 hours before the test
- Caffeine avoidance: No caffeine for 12-24 hours (if receiving pharmacologic stress)
- Medications: Ask about holding beta-blockers, calcium channel blockers, or theophylline
- Comfortable clothing: Wear exercise clothes and shoes for treadmill stress
- Diabetes: Special instructions for diabetic patients
Day of the Procedure
The test takes 3-5 hours:
- Preparation: IV placement, baseline ECG
- Stress: Exercise or pharmacologic stress with tracer injection
- Stress imaging: SPECT acquisition (15-30 minutes)
- Rest imaging: Waiting period then rest tracer injection and imaging
- Completion: Resume normal activities
Understanding Your Results
What Happens Next?
Cardiology Consultation
Discuss ischemia severity, symptoms, and treatment options including medical therapy versus invasive angiography with possible revascularization.
Optimization of Medical Therapy
Initiate or intensify antianginal medications including beta-blockers, calcium channel blockers, nitrates, and preventive medications (aspirin, statins).
Coronary Angiography
Invasive coronary angiography to visualize coronary anatomy and determine suitability for PCI (stenting) or CABG (bypass surgery).
Revascularization
PCI or CABG for high-risk anatomy with significant ischemia. Timing depends on symptom severity, ischemia burden, and anatomy.
Frequently Asked Questions
Is myocardial perfusion SPECT better than a stress echo?
Both tests are excellent for detecting CAD. SPECT MPI has higher sensitivity and better reproducibility, but stress echo is less expensive and avoids radiation. The choice depends on patient factors, local expertise, and the specific clinical question.
Can I drive after the test?
Yes, you can drive yourself home unless you received sedation for the test (which is uncommon). Most patients return to normal activities immediately after the test.
How much radiation am I exposed to?
The radiation dose is comparable to a CT scan of the chest (approximately 5-10 mSv depending on protocol). This is considered acceptable for the diagnostic information obtained. Newer cameras and protocols can reduce dose by 50-70%.
What if I can't exercise on a treadmill?
Pharmacologic stress agents are available for patients who cannot exercise. These medications dilate coronary arteries to simulate the stress of exercise and are equally effective for detecting CAD.
References
- American College of Cardiology. ACC/AHA Guidelines for Stable Chest Pain. 2024.
- American Society of Nuclear Cardiology. ASNC Imaging Guidelines for Nuclear Cardiology Procedures. 2023.
- Hage FG, et al. Clinical Application of Stress Myocardial Perfusion Imaging. JACC. 2024.
Medical Disclaimer: This information is educational only. Always discuss findings with your healthcare provider for personalized medical advice.
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