Reduced cardiopulmonary baroreflex sensitivity in patients with hypertrophic cardiomyopathy.

OBJECTIVES We sought to assess baroreflex function in patients with hypertrophic cardiomyopathy (HCM). BACKGROUND We have previously demonstrated a specific abnormality in the afferent limb of the cardiopulmonary baroreflex in patients with vasovagal syncope. Patients with HCM exhibit abnormal control of their vasculature during exercise and upright tilt; we therefore hypothesize a similar abnormality in the afferent limb of the cardiopulmonary baroreflex arc. METHODS We investigated 29 patients with HCM and 32 control subjects. Integrated baroreceptor sensitivity was assessed after administration of phenylephrine. Cardiopulmonary baroreceptor sensitivity was assessed by measuring forearm vascular resistance (FVR) during lower body negative pressure (LBNP). Carotid artery baroreflex sensitivity was assessed by measuring the in RR interval during manipulation of carotid artery transmural pressure. The integrity of the efferent limb of the reflex arc was determined by studying responses to both handgrip and peripheral alpha-receptor sensitivity. RESULTS During LBNP, FVR increased by only 2.36+/-9 U in patients, compared with an increase of 123+/-8.76 U in control subjects (p=0.001). FVR paradoxically fell in eight patients, but in none of the control subjects. Furthermore, FVR fell by 4.9+/-5.6 U in patients with a history of syncope, compared with an increase of 4.7+/-7.2 U in those without syncope (p=0.014). Integrated and carotid artery baroreflex sensitivities were similar in patients and control subjects (14+/-7 vs. 14+/-6 ms/mm Hg, p=NS and -3+/-2 vs. -4+/-2 ms/mm Hg, p=NS, respectively). Similarly, handgrip responses and the dose/response ratio to phenylephrine were not significantly different. CONCLUSIONS This study suggests that patients with HCM have a defect in the afferent limb of the cardiopulmonary reflex arc.