Abnormal vascular responses to supine exercise in hypertrophic cardiomyopathy

Exercise hypotension has been documented in hypertrophic cardiomyopathy. It is not the result of an inability to augment cardiac output but instead relates to an inappropriate and exaggerated decrease in systemic vascular resistance at high work loads.

To enable us to examine the behavior of the peripheral vasculature during exercise, 103 consecutive patients underwent maximal symptom-limited supine bicycle exercise with measurement of forearm blood flow. A minimum reduction of 12% from the basal value was defined as a normal response based on the study of 25 normal controls. In the patients, two patterns of forearm blood flow were observed. Sixty-four patients had an appropriate reduction in forearm blood flow of 40 +/- 16% from resting flow. In 39 patients, the forearm blood flow either failed to decrease or increased with exercise by 45 +/- 105% of the resting value. Patients with an abnormal forearm vasodilator response were younger (31 +/- 13 versus 46 +/- 14 years), and more of them had a family history of hypertrophic cardiomyopathy and sudden death than did those with a normal vasoconstrictor response (16 of 39 versus eight of 64). Left ventricular end-diastolic cavity dimensions were smaller in those with an abnormal forearm blood flow response, but other clinical, echocardiographic, and arrhythmic variables were similar. To assess the relation of abnormal peripheral vascular responses to erect exercise blood pressure response, patients underwent treadmill exercise testing with careful monitoring of systolic blood pressure response. Thirty-eight patients had significant exercise hypotension with failure of the systolic blood pressure to increase during progressive exercise (n = 6) or an abrupt decrease in systolic blood pressure (20-60 mm Hg) from the peak value (n = 32); 65 patients had a normal exercise blood pressure response, but 18 of these patients had an oscillation in systolic blood pressure of 10 mm Hg or more early in the recovery phase. Thirty-one of 39 patients with an abnormal forearm blood flow response demonstrated exercise hypotension during the erect exercise testing, and the remaining eight patients had a normal exercise blood pressure response; however, five of these eight had abnormal oscillations in blood pressure during recovery (r = 0.61, p less than 0.001).

The relation of abnormal peripheral vascular responses to exercise hypotension confirms the observation of hemodynamic instability in patients with hypertrophic cardiomyopathy. The finding of abnormal vascular responses in patients known to be at increased risk (young age and a family history of hypertrophic cardiomyopathy and sudden death) suggests that hemodynamic mechanisms may be important in the occurrence of sudden death in hypertrophic cardiomyopathy.