Sestamibi vs. LexiScan: Understanding the Distinction
Sestamibi (Technetium-99m sestamibi) is a radioactive tracer used to visualize myocardial perfusion, while LexiScan (regadenoson) is a pharmacologic stress agent used to induce coronary vasodilation—they serve completely different but complementary roles in cardiac stress testing. 1
Key Conceptual Difference
Sestamibi: The Imaging Agent
- Sestamibi is a Technetium-99m-labeled radiopharmaceutical that acts as the "camera dye" to visualize blood flow distribution in the heart muscle during SPECT imaging 1, 2
- It emits gamma rays at 140 keV with a 6-hour half-life, providing superior image quality compared to older agents like Thallium-201 1, 2
- Sestamibi does NOT induce stress—it simply accumulates in myocardial tissue proportional to blood flow at the moment of injection 3
- The typical effective radiation dose ranges from 9.8 to 16.3 mSv for a complete rest-stress protocol 1, 2
LexiScan: The Stress Agent
- LexiScan (regadenoson) is a pharmacologic vasodilator that creates the "stress" by dilating normal coronary arteries more than diseased ones, revealing perfusion defects 1
- It belongs to the adenosine receptor agonist class and works by producing regional differences in coronary blood flow 1
- LexiScan is used when patients cannot exercise adequately due to physical limitations, advanced age, or obesity 1
How They Work Together in Clinical Practice
The complete test requires BOTH components:
The Stress Phase
- LexiScan is administered intravenously to induce maximal coronary vasodilation 1
- At peak vasodilation, Sestamibi is injected and distributes according to regional myocardial blood flow 1
- SPECT imaging is performed 15-60 minutes later to capture the stress perfusion pattern 1
The Rest Phase
- A separate resting Sestamibi injection is given (typically on a different day to minimize radiation) 1
- Rest images are compared to stress images to identify reversible ischemia versus fixed infarction 1
Clinical Advantages of This Combination
Technetium-99m sestamibi with pharmacologic stress demonstrates excellent diagnostic accuracy:
- Sensitivity of 91% and specificity of 86% for detecting significant coronary stenoses in women 1
- Sensitivity of 95% and specificity of 75% for detecting CAD ≥70% stenosis in elderly patients (>80 years) 4
- Particularly valuable in patients with left bundle-branch block or paced rhythm, where vasodilator stress (like LexiScan) with sestamibi imaging is preferred over exercise testing 1
Alternative Stress Agents (Not Sestamibi)
Other pharmacologic stress agents that could be used instead of LexiScan include:
- Adenosine (direct coronary vasodilator, similar mechanism) 1
- Dipyridamole (indirect coronary vasodilator) 1
- Dobutamine (increases cardiac contractility and heart rate, different mechanism) 1
Alternative Imaging Agents (Not LexiScan)
Other radiopharmaceuticals that could be used instead of Sestamibi include:
- Tc-99m tetrofosmin (equivalent prognostic accuracy to sestamibi) 2, 5
- Rubidium-82 for PET imaging (lower radiation: 3.3-3.8 mSv, but requires PET scanner) 2
- Nitrogen-13 ammonia for PET (excellent for quantification, requires on-site cyclotron) 2
Common Clinical Pitfall
The most common confusion is thinking "Sestamibi stress test" means Sestamibi causes the stress—this is incorrect. The stress is induced by exercise OR a pharmacologic agent like LexiScan, while Sestamibi simply serves as the imaging tracer to visualize the resulting perfusion pattern 1.