What are the recommended steps for the stress portion of a myocardial perfusion imaging study, including administration of regadenoson (Lexiscan), radiotracer injection, and saline flush?

Regadenoson (Lexiscan) Stress Protocol for Myocardial Perfusion Imaging

For myocardial perfusion imaging with regadenoson (Lexiscan), the correct sequence is: inject 0.4 mg regadenoson IV over 10 seconds, immediately follow with a 5 mL saline flush, then inject the radiotracer 10-20 seconds after the saline flush. 1

Step-by-Step Protocol

1. Regadenoson Administration

• Administer 0.4 mg (5 mL) regadenoson as an IV bolus over 10 seconds into a peripheral vein using a 22-gauge or larger catheter 1
• This is a fixed dose regardless of patient weight 2
• The 10-second injection time is critical—longer injection times may increase the duration and magnitude of coronary blood flow increase 1

2. Immediate Saline Flush

• Administer a 5 mL saline flush immediately after the regadenoson injection 1
• This ensures complete drug delivery into the circulation 2

3. Radiotracer Injection

• Inject the radionuclide 10-20 seconds after the saline flush 1
• The radiotracer may be injected directly into the same catheter used for regadenoson 1
• Optimal timing for image acquisition is 2-4 minutes after drug infusion 2

Key Advantages of This Protocol

The regadenoson protocol is simpler than traditional vasodilator stress agents because:

• No infusion pump required—administered by hand-held syringe 2
• Fixed bolus dose simplifies workflow compared to weight-based adenosine or dipyridamole dosing 2
• Rapid administration minimizes staff exposure time and patient contact, which was particularly valuable during the COVID-19 pandemic 3

Important Timing Considerations

Peak vasodilatory effect occurs rapidly with regadenoson due to its selective A2A receptor agonism 2. Unlike dipyridamole (where peak effect occurs 1-6 minutes after infusion ends), regadenoson's effects are immediate, making the 10-20 second window for radiotracer injection critical for capturing peak hyperemia 2.

Common Pitfall to Avoid

Do not delay the saline flush or radiotracer injection. The sequence must be rapid and continuous: regadenoson → immediate saline flush → radiotracer 10-20 seconds later. Any delay may result in suboptimal imaging as you miss the peak vasodilatory window.

Pre-Procedure Requirements

• Patients must avoid methylxanthines (caffeine, aminophylline, theophylline) for at least 12 hours before the study 1
• Have aminophylline available as an antidote if serious adverse reactions occur 1
• Ensure cardiac resuscitation equipment and trained staff are immediately available 1