Is it okay to switch to Lexiscan (regadenoson) for a pharmacologic stress test in a patient with a history of CABG and PCI, now experiencing dizziness and orthostatic hypotension?

Switching to Lexiscan (Regadenoson) for Pharmacologic Stress Testing

Yes, it is appropriate and guideline-recommended to switch to Lexiscan (regadenoson) for pharmacologic stress imaging in this patient who became lightheaded during exercise stress testing and has documented orthostatic hypotension. 1

Guideline-Based Rationale for Switching

Pharmacological stress imaging with nuclear MPI or echocardiography is recommended (Class I) for patients with known stable ischemic heart disease who have new or worsening symptoms and are incapable of at least moderate physical functioning or have disabling comorbidity. 1 Your patient's inability to complete 4 minutes of treadmill exercise due to lightheadedness, combined with documented orthostatic hypotension, clearly establishes him as unable to achieve an adequate workload for diagnostic exercise stress testing. 1

The ACC/AHA guidelines explicitly state that pharmacological stress imaging should NOT be performed in patients capable of adequate exercise (Class III: No Benefit), but conversely, it IS recommended when patients cannot exercise adequately (Class I). 1 Your patient's symptomatic lightheadedness at less than 4 minutes of exercise demonstrates inadequate exercise capacity, making him an appropriate candidate for pharmacologic stress. 1

FDA-Approved Indication

Regadenoson (Lexiscan) is FDA-approved specifically for radionuclide myocardial perfusion imaging in patients unable to undergo adequate exercise stress. 2 The FDA label explicitly studied regadenoson in patients following inadequate exercise stress, defining adequate exercise as ≥85% maximum predicted heart rate and ≥5 METS. 2 Your patient's inability to complete the treadmill protocol due to symptoms fits this indication precisely.

Clinical Trial Evidence Supporting This Approach

The pivotal trials for regadenoson included patients with cardiovascular histories highly similar to your patient: 2

• 51% had prior CABG, PTCA, or stenting (your patient has both CABG and PCI 15 years ago)
• 63% had angina
• 41% had history of myocardial infarction
• 81% had hypertension

Regadenoson demonstrated equivalent diagnostic accuracy to adenoscan (6-minute infusion) with agreement rates of 62-63% compared to 61-64% for adenoscan. 2 Importantly, the FDA specifically evaluated regadenoson administered after inadequate exercise stress, validating the exact clinical scenario you're facing. 2

Critical Safety Considerations for Orthostatic Hypotension

Your patient's orthostatic hypotension requires specific management considerations:

Before proceeding with pharmacologic stress:

• Ensure adequate hydration status, as regadenoson can cause transient hypotension 3
• Have the patient supine during and immediately after regadenoson administration to minimize orthostatic symptoms 3
• Monitor blood pressure closely during the procedure, as vasodilator stress agents can exacerbate hypotension 4, 3

The orthostatic hypotension itself may be contributing to his dizzy spells and should be evaluated separately from his cardiac symptoms. 5, 3 Orthostatic hypotension is defined as a decrease in systolic BP of 20 mmHg or diastolic BP of 10 mmHg within 3 minutes of standing. 3 Common symptoms include dizziness, lightheadedness, blurred vision, and weakness—all potentially relevant to his presentation. 3

Practical Algorithm for This Patient

1. Confirm orthostatic vital signs (supine, sitting, standing at 1 and 3 minutes) to quantify the degree of orthostatic hypotension 3

2. Optimize volume status before the pharmacologic stress test—ensure adequate hydration 3

3. Review medications that may contribute to orthostatic hypotension (diuretics, alpha-blockers, vasodilators) 4, 3

4. Proceed with regadenoson stress nuclear MPI or echocardiography as recommended by guidelines 1

5. Keep patient supine during and for at least 10-15 minutes after regadenoson administration 3

6. Have aminophylline available to reverse regadenoson effects if severe hypotension or other adverse effects occur 2

Common Pitfalls to Avoid

Do not attempt to push this patient to complete a full exercise stress test when he is symptomatic at submaximal workload—this provides neither adequate diagnostic information nor appropriate risk stratification and may be dangerous. 1

Do not assume the lightheadedness is purely cardiac—orthostatic hypotension is a separate entity that requires evaluation and management, potentially with fludrocortisone, midodrine, or nonpharmacologic measures. 5, 3, 6

Do not overlook that his history of CABG and PCI 15 years ago places him at higher risk for recurrent ischemia, making accurate stress testing particularly important for risk stratification. 1