Target Heart Rate for Lexiscan (Regadenoson)
There is no specific target percentage heart rate increase required for Lexiscan (regadenoson) as it functions through selective coronary vasodilation rather than heart rate manipulation. Unlike exercise stress testing, which aims for specific heart rate targets, regadenoson works by directly causing coronary vasodilation regardless of heart rate response.
Mechanism of Action and Expected Heart Rate Response
Regadenoson is a selective A2A adenosine receptor agonist that causes:
- Direct coronary vasodilation in normal epicardial arteries 1
- A rapid increase in coronary blood flow that is sustained for a short duration 2
- Typically, a modest increase in heart rate (10-12 beats per minute in atrial fibrillation patients) 1
Unlike dobutamine stress testing, which aims for 85% of age-predicted maximum heart rate 1, regadenoson's effectiveness is not dependent on achieving a specific heart rate target.
Heart Rate Response Variations
Several factors can affect heart rate response to regadenoson:
- Diabetes mellitus: Patients with diabetes show a blunted heart rate response (29.4% vs 36.1% increase in non-diabetics) 3
- Insulin therapy: Further blunts heart rate response (25.9% vs 31.2% in non-insulin-dependent diabetics) 3
- Obesity: Patients with BMI ≥30 kg/m² show a blunted heart rate response 4
However, these variations in heart rate response do not affect the diagnostic accuracy of the test, as regadenoson's primary mechanism is coronary vasodilation rather than heart rate manipulation.
Safety Considerations
Regadenoson is generally well-tolerated:
- Most adverse events begin soon after administration and resolve within approximately 15 minutes 2
- Common symptoms include dyspnea (30%), chest discomfort (27%), and headache (15%) 4
- Minimal changes in systolic and diastolic blood pressure 4
- Safe for use in patients with mild/moderate COPD and asthma, though caution is advised 5, 6
Clinical Implications
- Unlike exercise stress testing where specific heart rate targets are essential (e.g., 50-75% of maximum heart rate as shown in Table 2 of reference 1), regadenoson's effectiveness does not depend on achieving a specific heart rate
- Monitoring of heart rate, blood pressure, and symptoms is still important during the test 4
- The test can proceed successfully regardless of the magnitude of heart rate increase
In conclusion, while regadenoson typically causes a modest increase in heart rate, there is no specific target percentage heart rate increase required for the test to be diagnostically valid, as its primary mechanism is direct coronary vasodilation rather than heart rate manipulation.