The Outcome of Exercise Tolerance Testing is Dependent on the Time of the Day

Background Although exercise testing is commonly used to identify patients with an increased risk for ischemic events and to evaluate drug therapy, no reports have clearly addressed whether a daily variation exists in exercise test parameters. Therefore the present study was undertaken, analyzing the effects of the time of the day on exercise test parameters in a large population of cardiovascular patients. Methods We compared the responses of bicycle exercise testing in 6674 patients, mean age 60 years, referred for evaluation of coronary artery disease. The daily variation was tested by grouping the exercise variables into four 2-hour periods. Further logistic regression analysis was used to assess predictors for the occurrence of ischemia. Results Significant time of the day differences were found both at rest and in their changes to peak exercise for heart rate (P < 0.0001 and P < 0.0004), systolic blood pressure (P < 0.0001 and P < 0.0003), and diastolic blood pressure (P < 0.004 and P < 0.0001). Furthermore, ischemia occurred significantly more often during the afternoon intervals (P < 0.009) and time of the day was an independent predictor of ischemia during exercise testing. Conclusion The present study demonstrates that several exercise parameters show a significant daytime variation. The time of the day is an independent predictor for the occurrence of ischemia during an exercise test, and the detection of ischemia may be enhanced by performing exercise tests in the afternoon.