What is the recommended dosing, contraindications, monitoring requirements, common adverse effects, and reversal protocol for Lexiscan (regadenoson) used as a pharmacologic stress agent for myocardial perfusion imaging?

Lexiscan (Regadenoson) for Myocardial Perfusion Imaging

Recommended Dosing

Administer regadenoson as a fixed dose of 0.4 mg (5 mL) via rapid intravenous injection over 10 seconds, followed immediately by a 5 mL saline flush, with the radionuclide tracer injected 10-20 seconds after the saline flush. 1

• Use a 22-gauge or larger peripheral catheter or needle for administration 1
• No weight-based dosing adjustment is required, simplifying administration compared to adenosine 2, 3
• The radionuclide may be injected directly into the same catheter as regadenoson 1
• SPECT imaging is typically performed 60-90 minutes after regadenoson administration 2
• The 10-second injection time is critical; longer injection times may increase the duration and magnitude of coronary blood flow, potentially increasing adverse effects 1

Absolute Contraindications

Do not administer regadenoson to patients with second- or third-degree AV block or sinus node dysfunction unless they have a functioning artificial pacemaker. 1

• Active bronchospasm or severe reactive airway disease with recent wheezing is an absolute contraindication to vasodilators 4
• Systolic blood pressure <90 mmHg contraindicates vasodilator use 4
• Avoid use in patients with acute myocardial ischemia, unstable angina, or cardiovascular instability, as these patients are at greater risk for serious cardiovascular reactions including MI and cardiac arrest 1, 5

Pre-Procedure Patient Preparation

Patients must avoid all methylxanthine-containing products for at least 12-24 hours before the test, including caffeinated coffee, tea, other caffeinated beverages, caffeine-containing drugs, aminophylline, and theophylline. 1, 4

• Patients should be NPO for 4 hours prior to the test, with a light meal acceptable for diabetics 4
• Continue beta-blockers and other cardiac medications unless specifically contraindicated 4
• Inspect the regadenoson solution visually for particulate matter or discoloration before administration; do not use if present 1

Monitoring Requirements

Continuous 12-lead ECG monitoring is mandatory from baseline through recovery, with blood pressure measured at baseline, peak stress, and every 2-3 minutes during recovery. 4

• Heart rate monitoring should be continuous throughout the procedure 4
• Oxygen saturation monitoring is indicated if the patient has pulmonary disease or heart failure 4
• Cardiac resuscitation equipment and trained staff must be available before administering regadenoson 1

Common Adverse Effects

Most adverse effects begin soon after administration and resolve within approximately 15 minutes; the most frequent complaints are dyspnea, flushing, and chest discomfort. 6, 7

• Regadenoson causes a rapid increase in heart rate that is faster and greater than with adenosine, but with slower return to baseline 6
• Slight decreases in systolic and diastolic blood pressure occur, with slower recovery to baseline compared to adenosine 6
• Overall symptom severity and duration are significantly lower with regadenoson compared to adenosine (symptom score 6.7±6.3 vs. 10.0±7.9, p<0.01) 7
• Fewer patients experience severe complaints with regadenoson than adenosine (17% vs. 32%, p<0.01) 7
• High-grade atrioventricular block and bronchospasm were not observed in initial clinical trials 8

Critical caveat: Rare but serious adverse effects including asystole with hemodynamic collapse, fatal and nonfatal myocardial infarction, ventricular arrhythmias, and cardiac arrest have been reported, even in stable outpatients 1, 5. The prevalence of potentially life-threatening bradycardia may be greater than previously expected 5.

Mandatory Test Termination Criteria

Immediately terminate the test for significant ST-segment depression (≥2 mm) or elevation (≥1 mm), moderate to severe angina or intolerable symptoms, systolic blood pressure drop >20 mmHg from baseline, or severe hypertension (>200/110 mmHg). 4

• Any development of second- or third-degree AV block requires immediate termination 1
• Sinus bradycardia requiring intervention mandates stopping the procedure 1

Reversal Protocol

If serious reactions occur, consider administering aminophylline, an adenosine antagonist, to shorten the duration of increased coronary blood flow induced by regadenoson. 1, 4

• Aminophylline must be immediately available at bedside before starting the test 4
• Standard emergency medications including nitroglycerin, atropine, and full advanced cardiac life support medications and equipment should be available 4
• Esmolol should be available for managing tachycardia if needed 4

Clinical Advantages

Regadenoson demonstrates non-inferiority to adenosine for detecting reversible myocardial perfusion defects with an 86% overall agreement rate, while offering superior tolerability and procedural simplicity. 8, 3

• The American College of Cardiology prefers regadenoson over exercise MPI in patients with left bundle-branch block due to higher specificity 2
• Normal or mildly abnormal results indicate an annual risk for cardiac death and acute MI less than 1% 2
• The negative predictive value of pharmacologic stress perfusion imaging is high, typically 90-100% 2
• Moderate to severe abnormalities (multivessel perfusion defects) predict an annual risk for cardiovascular death or MI of 5% or higher 2