An analysis of the left ventricular response to isometric exercise

Analysis of the left ventricular response to isometric exercise was performed in a group of patients undergoing diagnostic cardiac catheterization. A normal response was observed in nine patients with normal resting hemodynamics (Group I). This response consisted of a significant increase in LV stroke work associated with minor changes (average increase of 2 mm. Hg) in LV end-diastolic pressure. Significant increases were consistently observed in the isovolumic indices of myocardial contractility. These findings indicate that the normal left ventricle responds to this form of exercise by improving its contractile state and to a minor degree by increasing preload, thus maintaining a constant stroke volume in the presence of an increased afterload. To test whether the increase in contractility observed during isometric exercise was related to the increase in heart rate, isovolumic indices of contractility were measured in eight patients during atrial pacing at a rate equal to that achieved during exercise. Isometric exercise was associated with a higher level of myocardial contractility than atrial pacing. In addition, a significant improvement in the isovolumic indices was observed in four out of five patients subjected to isometric exercise at a constant heart rate (atrial pacing). Thus, it seems that in addition to the "treppe" effect, other factors independent of heart rate are involved in augmenting myocardial contractility during isometric exercise. Ten patients (Group II) responded to exercise with a marked increase in LVEDP but little change in LV stroke work; five patients (Group III) responded with only a minor change in LVEDP (similar to Group I) but with no improvement in LV stroke work. Myocardial contractility also failed to increase in most of these patients. Isometric exercise uncovered abnormalities of LV performance not identified by the resting hemodynamics in a significant number of patients.