Myocardial oxygen demands of job activities in post-myocardial infarct patients

In 17 patients who returned to work following rehabilitation after an uncomplicated acute myocardial infarction (AMI), the myocardial oxygen demands (MOD) of various job activities were assessed using discontinuous ambulatory heart rate (HR) and blood pressure measurements. All patients were on beta-blocking agents. HR and rate-pressure product (RPP) reserves were calculated as the differences between maximal values observed during a symptom-limited maximal bicycle exercise test and basal values. Basal values were either pre-test resting values or mean values from night-time registrations between 0100h and 0500h. Night-time values of basal HR and RPP were 7.7 and 18.7% lower respectively as compared to pre-test resting values. The myocardial energy demands of various job activities were calculated as the percentage use of the reserves. This resulted in lower MOD estimations when pre-test values were used as compared to night-time values. These differences were larger for the estimation of MOD of light physical work (mean difference 25%) than for heavy physical work (mean difference 12%). The estimations of MOD using HR reserve or RPP reserve were very similar. In patients who performed the same job activities no correlation was found between MOD and left ventricle ejection fraction. We believe these data provide useful information about the functional capacity of AMI patients. They also emphasise the great importance that has to be attached to the definition of basal values.