Exercise prescription in cardiac patients treated with metoprolol - should the time of day for stress tests and training coincide?
Abstract
Background: Research indicates that heart rate (HR) varies throughout the day when patients taking metoprolol exercise on a treadmill, but research on cycle ergometry is lacking. Therefore, this study determined whether the time of cycle ergometry stress tests affects HR in cardiac patients treated with metoprolol.
Design: Eighteen sedentary patients (ten women and eight men, 62.72+-7.23 yr) treated with metoprolol performed two identical exercise tests on a cycle ergometer on separate days, in random order: in the morning (AM) and the afternoon (PM). Methods: Blood pressure, HR, ECG, ratings of perceived exertion (RPE), and respiratory gas exchange were monitored in both tests.
Cardiovascular rehabilitation prescriptions were then computed from HR data received from both tests. Results: Resting and submaximal-exercise HR were significantly lower (p<0.05) in the AM.
The HR at ventilatory threshold (VAT) was lower (105.75+-12.00) during AM than PM (113.00+-11.73 beats.min-1) (p<0.001). Maximum HR was lower (128.33+-19.67) during AM than PM (141.83+-18.95 beats.min-1) (p<0.001), but relative HR (%HRpeak and %HRreserve) was not different at submaximal workloads.
Peak oxygen consumption, respiratory exchange ratio, blood pressure, and RPE were similar in both tests. In some patients, exercise prescriptions from AM results would be too low for PM exercise training, whereas prescriptions from PM results would result in HR values approaching or surpassing VAT during AM training.
Conclusions: Therefore, the HR response to cycle ergometry varies during the day and should not be used to prescribe exercise therapy in patients treated with metoprolol unless the time of testing and training coincide. It is also important that cardiac rehabilitation specialists consider the inter-individual responses to beta-blocker therapy when prescribing HR-based exercise, as the peak plasma concentration of metoprolol differs between slow and fast metabolizers.