Changes in Oxygen Consumption and Heart Rate After Acute Myocardial Infarction During 6-Month Follow-up.

BACKGROUND: Exercise intensity is a particularly important determinant of physiological responses to exercise training in patients with acute myocardial infarction. Heart rate (HR) is commonly used as a practical way of prescribing and monitoring exercise as specific intensities based on a linear relationship between the percentage of maximum HR (%HRmax ) and the percentage of maximum oxygen consumption (%VO2max ) regardless of age, gender, or exercise mode.

OBJECTIVE: To examine the change in variability in the correlation between %HRmax and %VO2max after acute myocardial infarction.

DESIGN: Retrospective study.

SETTING: Regional cardio-cerebrovascular center at a tertiary hospital.

PATIENTS: A total of 66 patients were enrolled who were referred for cardiac rehabilitation (CR) after percutaneous intervention, and who had reached stage 3 of the modified Bruce Protocol (mBP) on an exercise tolerance test (ETT).

METHODS: There were 54 men and 12 women with an average age of 56.7 ± 9.48 years, ejection fraction (EF) of 56.4% ± 8.89%, and body mass index (BMI) of 24.73 ± 2.86 kg/m2 . All patients participated in a 4-week outpatient CR program and underwent ETT with a gas analyzer to determine maximal heart rate and maximal oxygen consumption before CR and 1 month, 3 months, and 6 months after CR.

MAIN OUTCOME MEASUREMENTS: VO2max and HRmax were defined as the highest values attained during the ETT. The HR and VO2 values at each stage of the mBP were expressed as percentages of their maximum. %HRmax and %VO2max were calculated at each stage of the mBP.

RESULTS: The maximum METs and VO2max significantly improved at 1 month after CR, but not significantly at 3 and 6 months after CR. The correlation between VO2max and HRmax progressively changed in a favorable manner during CR. The relationship between %HRmax and %VO2max indicated a coefficient of variation before and 1, 3, and 6 months after of 0.800, 0.826, 0.832, and 0.880, respectively.

CONCLUSIONS: This study showed that the %HRmax correlates better with the %VO2max in the late-stage post-AMI than in the initial stage. We should therefore set and monitor the exercise intensity using maximal oxygen consumption in the early stage of exercise training after onset of acute myocardial infarction.

LEVEL OF EVIDENCE: IV.