Impaired exercise performance but normal skeletal muscle characteristics in female syndrome X patients

Pathophysiologic mechanisms in syndrome X (anginal chest pain, positive exe rcise stress test, and angiographically normal coronary arteries) have been extensively studied. Recent reports suggest an ischemic origin of the pain to be less probable. Other contributing mechanisms that have been hypothes ized are enhanced sympathetic drive or sensitivity or an abnormal muscle me tabolism. Our aim in this study was to characterize exercise performance, s keletal muscle characteristics, and sympathetic control of blood flow in pa tients with syndrome X. Seven female patients aged 50 to 65 years and 5 mat ched controls were rested. Exercise test was performed according to clinica l routine. Plasma catecholamine and blood lactate levels were measured befo re, during, and offer exercise. Autonomic blood flow control was measured p lethysmographically in the resting contralateral forearm during isometric h andgrip. Muscle biopsy specimens were obtained at rest from the lateral par t of Musculus vastus at midthigh. The biopsy samples were investigated for the relative number of different fiber types, phosphagen content, and energ y charge, calculated as (adenosine triphosphate + 1/2 adenosine diphosphate )/[adenosine triphosphate + adenosine diphosphate + adenosine monophosphate ]). Exercise capacity was markedly decreased in syndrome X compared with co ntrols (85 +/- 14 vs 156 +/- 11 W, p <0.0005) and all patients discontinued exercise because of chest pain (Borg CR-10, 5 +/- 3). Peak heart rare was lower in syndrome X (150 +/- 18 vs 176 +/- 7 beats/min, p <0.01), whereas s ystolic blood pressure and double product did not differ. Peak norepinephri ne plasma levels were lower than in controls (11 +/- 6 vs 24 +/- 13 nmol/L, p <0.04), whereas peak blood lactate levels did not differ. Blood flow inc rease in the resting forearm during isometric handgrip was similar to that in controls. The proportion of different fiber types, phosphagen content, a nd energy charge were normal. Thus, patients with syndrome X have a reduced physical exercise capacity but no skeletal muscle abnormalities. Catechola mine hypersensitivity may contribute to their condition. (C) 1999 by Excerp ta Medica, Inc.