Diurnal variation in symptom-limited exercise test responses six weeks after myocardial infarction.

Diurnal variation of exercise test responses occurring during symptom-limited treadmill exercise testing was investigated in 45 patients six weeks after myocardial infarction. Each patient was exercised using a Naughton protocol before 8 a.m. and after 6 p.m. on the same day. No complications arose. There was no significant diurnal variation of any of the analysed exercise induced ischaemic abnormalities (angina pectoris or ST segment shift) or of the mean maximal exercise durations and achieved workloads. Mean maximal heart rates and heart rate-systolic blood pressure double products were similar in both tests. ST segment depression occurred in 21 patients and was totally consistent in both tests. An abnormal blood pressure response occurred in 14 patients in the morning test and in 18 patients in the evening test but this discordance did not reach statistical significance. Similarly there was no significant diurnal variation in exercise induced ventricular arrhythmias, although only three of the 11 patients in whom they occurred had this abnormality on both tests. We conclude that in this group of patients, no significant diurnal variation was observed in either exercise induced ischaemic abnormalities or in exercise haemodynamics during symptom-limited exercise tests performed six weeks after myocardial infarction. These data increase the confidence in clinical management decisions based on the results of this test.