The postextrasystolic murmur response to gradient in hypertrophic cardiomyopathy

Fourteen patients with hypertrophic cardiomyopathy, 40 with aortic stenosis, and 4 with discrete subaortic stenosis had phonocardiograms during left heart catheterization that showed changes in the magnitude of the murmur in response to increases in the postextrasystolic gradient. All patients showed increases in the gradient of the left ventricular outflow tract during the postextrasystolic beat. Of the 44 patients with aortic stenosis and discrete subaortic stenosis, 42 (95%) had increases in murmur magnitude, in contrast to 9 (64%) of 14 patients with hypertrophic cardiomyopathy. Only 2 of 7 patients with hypertrophic cardiomyopathy and resting gradients of more than 25 mm Hg had murmur increases. Our study shows that the systolic murmur in hypertrophic cardiomyopathy, unlike the outflow tract murmur in aortic stenosis or discrete subaortic stenosis, does not track consistently with the magnitude of the outflow tract gradient.