Background: We assessed the hemodynamic effects of isometric exercise by an ambulatory radionuclide monitoring device (VEST) that measured left ventricular function in patients who had hypertrophic cardiomyopathy (HCM), with and without significant left ventricular outflow-tract obstruction at rest, compared with control subjects.
Methods and results: We studied 10 patients with obstructive HCM, 25 patients with nonobstructive HCM, and 11 control subjects. During VEST monitoring, all patients gripped a dynamometer at 75% of maximal strength for up to 5 minutes. End-diastolic, end-systolic, and stroke volumes; cardiac output; and systemic vascular resistance were expressed as a percentage of baseline. The mean exercise duration was similar among the 3 groups. During handgrip, heart rate, systolic blood pressure, and cardiac output increased significantly and similarly in the 3 groups. There was a significant difference in the lung activity between obstructive and nonobstructive HCM patients and control subjects (P <.001), with a fall in control subjects and no change in HCM patients, irrespective of obstruction. Control subjects showed a decrease in end-systolic volume (P =.02) and an increase in ejection fraction (P =.003) and stroke volume (P =.009), whereas these parameters did not change in HCM patients, irrespective of obstruction. Systemic vascular resistance increased in obstructive (P =.02) and nonobstructive (P <.01) HCM patients but did not change in control subjects.
Conclusions: Isometric exercise causes an abnormal and similar adaptation to load changes in obstructive and nonobstructive HCM patients, as compared with control subjects.