External carotid pulse recordings in hypertrophic obstructive cardiomyopathy.

External carotid pulse tracings were examined in 15 patients with hypertrophic obstructive cardiomyopathy (HOCM), the diagnosis being confirmed by catheterization of the left heart. Of 12 patients with intraventricular gradients at rest, 9 had a typical bifid pulse with midsystolic dipping. In one patient without a gradient at rest, midsystolic dipping occurred only in beats following extrasystoles (Brockenbrough phenomenon). The upstroke of the pulse wave was rapid in all the patients, a finding that distinguishes them from patients with valvular aortic stenosis. There was a correlation between the length of the left ventricular ejection time and the intraventricular gradient (r = 0.71) but as more than half the patients had normal or shortened ejection times, the diagnosis of HOCM cannot be based on measurements of this parameter. It is concluded that carotid pulse registrations are of considerable diagnostic value in patients suspected of having HOCM. As the pulse changes are correlated to the degree of left ventricular outflow obstruction, it is suggested that repeated pulse tracings may be used as a means for controlling the degree of obstruction once the diagnosis has been established in the individual patient.