What is the difference between Lexiscan (regadenoson) and sestamibi (technetium-99m sestamibi) in myocardial perfusion imaging?

Differences Between Lexiscan (Regadenoson) and Sestamibi (Technetium-99m Sestamibi) in Myocardial Perfusion Imaging

Lexiscan (regadenoson) and sestamibi (technetium-99m sestamibi) serve completely different functions in myocardial perfusion imaging - regadenoson is a pharmacologic stress agent while sestamibi is a radiotracer that visualizes myocardial perfusion.

Lexiscan (Regadenoson)

• Lexiscan is a selective A2A adenosine receptor agonist used as a pharmacologic stress agent to induce coronary vasodilation when physical exercise is not possible or adequate 1, 2
• It functions by selectively binding to adenosine receptors in coronary arteries, causing coronary dilation and increasing coronary blood flow 1
• Regadenoson is administered as a single rapid intravenous bolus (typically 400 μg), with hyperemic effects lasting approximately 2-5 minutes, which is significantly longer than adenosine 2, 3
• After injection, regadenoson can increase coronary blood flow velocity by up to 3.4-fold in a dose-dependent manner 3
• Common side effects include warmth, chest discomfort, shortness of breath, headache, and flushing, but these are generally mild and self-limiting 1
• Regadenoson has fewer respiratory side effects compared to non-selective adenosine agonists, making it safer for patients with respiratory conditions 1, 2

Sestamibi (Technetium-99m Sestamibi)

• Sestamibi is a radiotracer used to visualize myocardial perfusion during imaging procedures 4, 5
• It shows a linear relationship with coronary blood flow when administered intravenously, making it effective for detecting areas of reduced perfusion 5
• Unlike thallium-201, sestamibi has minimal redistribution over time, allowing delayed imaging after injection without significant change in the initial distribution pattern 5, 6
• Sestamibi SPECT imaging typically takes approximately 40 minutes for image acquisition 5
• The typical effective radiation dose range for a 1-day Tc-99m rest-stress imaging protocol is 9.8 to 16.3 mSv 5
• Studies have shown high sensitivity (93%) and specificity (70%) for detecting myocardial infarction using sestamibi SPECT imaging 5
• Sestamibi allows for simultaneous assessment of myocardial perfusion and ventricular function through gated studies 6

Clinical Application Together

• In a typical myocardial perfusion study, regadenoson is injected first to induce coronary vasodilation, followed by injection of sestamibi 1
• This combination allows visualization of perfusion defects that may not be apparent at rest 4
• The longer duration of hyperemia with regadenoson (2-5 minutes) provides adequate time for sestamibi distribution in the myocardium 2, 3
• Sestamibi's minimal redistribution property allows for delayed imaging after stress, which is particularly useful in acutely ill patients 4
• When compared to other perfusion tracers like Tc-99m tetrofosmin, sestamibi demonstrates better defect contrast and detection of reversible perfusion defects 7

Clinical Considerations

• Regadenoson's selective A2A agonism results in fewer side effects compared to non-selective adenosine agonists like dipyridamole 2
• Aminophylline can be used to attenuate the vasodilatory effects of regadenoson if necessary 3
• Sestamibi's properties allow for SPECT imaging, which is generally more accurate than planar imaging for diagnosing coronary artery disease 4
• The combination of regadenoson stress with sestamibi imaging provides comprehensive assessment of coronary artery disease, including perfusion defects, wall motion, and wall thickening 1, 6