What is a Lexiscan (regadenoson) scan stress test?

Lexiscan (Regadenoson) Scan Stress Test

A Lexiscan scan stress test is a pharmacologic stress test that uses regadenoson (brand name Lexiscan) to dilate coronary arteries and create blood flow heterogeneity between normal and stenotic vessels, allowing detection of myocardial perfusion defects during nuclear imaging in patients unable to perform adequate exercise stress testing. 1, 2

Mechanism of Action

• Regadenoson selectively binds to A2A adenosine receptors, causing coronary vasodilation in normal epicardial arteries while stenotic vessels cannot dilate to the same extent, creating detectable perfusion differences during imaging 2
• Unlike exercise stress which creates a supply-demand mismatch, regadenoson directly causes coronary vasodilation, unmasking locally limited capacity for vasodilation in diseased vessels 2
• This differential response creates heterogeneity in myocardial perfusion that can be visualized with nuclear imaging agents 2

Clinical Indications

• FDA-approved as a pharmacologic stress agent for radionuclide myocardial perfusion imaging in patients unable to undergo adequate exercise stress 3
• Particularly useful for patients with physical limitations who cannot achieve adequate exercise levels 1
• Recommended for patients with abnormalities on resting ECG that impair diagnostic interpretation, such as left bundle-branch block, LV hypertrophy with "strain" pattern, and digitalis effect 1
• Preferred over exercise MPI in patients with left bundle-branch block due to higher specificity 1

Procedure

• Administered as a single fixed-dose of 0.4 mg via intravenous injection, with no need for weight-based dosing 1
• Radionuclide tracer (typically 99mTc-sestamibi) is injected shortly after regadenoson administration 1
• SPECT imaging is performed 60-90 minutes after regadenoson administration 1, 3
• The pharmacologic stress perfusion endpoint achieved with regadenoson creates induced coronary flow heterogeneity used with various forms of myocardial perfusion imaging 4

Comparison to Other Stress Agents

• Regadenoson works differently from dobutamine, which increases myocardial oxygen demand through increased contractility and heart rate 2
• Unlike adenosine and dipyridamole (non-selective adenosine receptor agonists), regadenoson is selective for A2A receptors, potentially reducing side effects 5
• In phase III trials, regadenoson demonstrated non-inferiority to adenosine for detecting reversible myocardial ischemia 5
• Regadenoson causes a faster and greater peak increase in heart rate compared to adenosine, but with a slower return to baseline 6

Diagnostic Accuracy

• The agreement rate between regadenoson and adenosine in detecting reversible perfusion defects has been shown to be non-inferior in clinical trials 3, 6
• Pharmacologic stress perfusion imaging with agents like regadenoson has a high negative predictive value, typically 90-100% 1
• Normal or mildly abnormal results on myocardial perfusion imaging indicate an annual risk for cardiac death and acute MI less than 1% 1
• Moderate to severe abnormalities (multivessel perfusion defects) predict an annual risk for cardiovascular death or MI rates of 5% or higher 1

Safety Profile and Contraindications

• Generally well-tolerated, with most adverse events beginning soon after administration and resolving within approximately 15 minutes 6
• Contraindicated in patients with acute coronary syndrome or high-risk unstable angina 1
• Caution advised in patients with sinus node disease and second-degree heart blocks, as rare cases of advanced heart block, pulseless electrical activity, and asystole have been reported 7
• The FDA-approved dose does not appear to disrupt the blood-brain barrier in humans with intact BBB, unlike what has been observed in animal studies 8

Clinical Considerations

• Regadenoson is excreted unchanged in the urine (57%), with renal tubular secretion playing a role in elimination 3
• No dose adjustment is needed in elderly patients based on population pharmacokinetic analysis 3
• The use of intravenous ultrasound contrast agents can improve endocardial border delineation and diagnostic accuracy when used with stress echocardiography 4
• When appropriate, exercise-based stress testing is preferred to pharmacologically induced stress testing, but regadenoson provides a valuable alternative when exercise is impractical 4