Difference in the response to isoproterenol between asymmetric septal hypertrophy and symmetric hypertrophy in patients with hypertrophic cardiomyopathy

The response to isoproterenol was studied in 9 patients with hypertrophic cardiomyopathy (HCM) and asymmetric septal hypertrophy (ASH), 9 patients with HCM and symmetric hypertrophy (SH), and 9 normal controls (NC), using digitized M-mode echocardiography. There was no significant difference in fractional shortening (FS) between ASH and SH, nor between SH and NC before isoproterenol infusion. During isoproterenol infusion, however, FS was significantly greater in ASH (60 +/- 6%) than in SH (53 +/- 7%) and NC (49 +/- 5%) (p less than 0.05, p less than 0.01, respectively), and normalized peak rate of change of left ventricular dimension during systole (pVs) was greater in ASH (7.7 +/- 1.5/s) than in SH (5.2 +/- 0.8/s) and in NC (4.9 +/- 0.8/s) (p less than 0.001, p less than 0.001, respectively). This study shows that the response to isoproterenol of ASH differs from those of SH and of NC and suggests hypersensitivity of the beta-adrenergic receptor system in ASH and the possibility that ASH is a different clinical entity than SH.