Relation between marked changes in left ventricular outflow tract gradient and disease progression in hypertrophic cardiomyopathy.

Spontaneous and persistent changes in left ventricular (LV) outflow gradient have been observed occasionally in patients with hypertrophic cardiomyopathy (HC). However, the significance and frequency of such hemodynamic alterations have not been established. In this study, the serial preoperative hemodynamic status of 409 patients with HC was analyzed. Basal LV outflow tract obstruction either spontaneously appeared (or increased) or disappeared (or decreased) in 19 nonoperated patients (about 5%). Changes in hemodynamic state were shown by serial cardiac catheterization in 17 patients and by catheterization and M-mode echocardiography in 2 patients. In most patients (12 of 19), subaortic obstruction under basal conditions appeared or increased; 8 became more symptomatic and in 4 the condition remained stable. Reduction or loss of LV outflow gradient occurred in 7 patients; in 5 of these the condition deteriorated clinically and in 2 it did not change. Hence, in 13 of the 19 patients (70%), spontaneous changes in the magnitude of the basal LV outflow gradient were associated with symptomatic progression. The mechanism of the decrease or disappearance of subaortic obstruction in those patients who deteriorated clinically appeared to be related in 4 patients to impaired global and/or segmental LV function. Chronic atrial fibrillation probably contributed to the worsening clinical condition in 2 of these patients as well as in 2 others. In conclusion, substantial changes in the magnitude of basal subaortic obstruction may occur in a small proportion of patients with HC as part of the natural history of their disease, and such hemodynamic alterations are usually associated with clinical deterioration. It is exceedingly rare for the hemodynamic state of a patient with HC to change from totally nonobstructive to obstructive or vice versa, because such patients usually retain the capacity to generate gradients with provocative maneuvers.