Comparison of ventricular volumes in normal and post-myocardial infarction subjects.
In an effort to determine left ventricular volume changes between upright rest and exercise, 15 male late post-infarction patients (group A) and 13 normal matched volunteers (group B) were studied. Patients were at least 12 months post-cardiac event. Upright two-dimensional echocardiographic recordings were performed by the same cardiac sonographer using the apical four-chamber view at rest and immediately post-exercise after the subject reached 85% of measured maximal heart rate. Single-plane planimetry of the cross-sectional area was used for calculation of left ventricular volumes. Two subjects in each group failed to demonstrate adequate (i.e., measurable) echocardiograms and were excluded from the statistical analyses. Two-way analysis of variance for repeated measures was followed by the Newman-Kuels multiple comparison procedure to determine statistically significant differences between means (P less than 0.05). The results indicated no differences in any of the measured parameters at rest between the groups. Exercise values demonstrated a significant increase in end-diastolic volume, stroke volume, and ejection fraction with exercise only in group B. End-systolic volume did not change in either group. Cardiac output and heart rate increased in both groups. These data suggest that in the upright position, cardiac output increases in normal males due to an increase in heart rate and stroke volume (increases in end-diastolic volume) and by increases in heart rate alone in the post-infarction group.