Effect of epinephrine infusion on chest pain in syndrome X in the absence of signs of myocardial ischemia

Eight female patients (aged 51 to 65 years) with New York Heart Association class II angina pectoris, normal coronary angiograms, normal hyperventilation, and abnormal exercise stress tests (chest pain and ST depression), and 5 sex- and age-matched controls participated in this study. Epinephrine was given intravenously to both patients and controls at 5-minute intervals in doses of 0.1, 0.2, 0.3, 0.4, and 0.6 nmol/kg/min. After rest (15 minutes), the α-adrenoceptor antagonist phentolamine or placebo was administered intravenously to patients in a double-blind, crossover study on 2 separate occasions in doses of 250 μg/min for 5 minutes and 500 μg/min for the next 10 minutes; the epinephrine infusion was repeated. Blood pressure, heart rate, and electrocardiogram were monitored continuously and pain was estimated on the Borg CR-10 scale. On a third occasion, chest pain was induced in patients using the same epinephrine protocol during echocardiographic monitoring. In the control group, all patients received the maximal epinephrine dose. No chest discomfort or pain developed. In the patient group, the maximal tolerable epinephrine dose (0.39 ± 0.19 nmol/kg/min) decreased diastolic pressure (−14 ± 9 mm Hg, p <0.01) and increased heart rate (+24 ± 10 beats/min, p <0.01), not statistically different from the control group. Pulse pressure increased in the patient group (27 ± 17 mm Hg, p <0.01) but not in the controls. Left ventricular ejection fraction at baseline was within reference limits (58% to 75%) and did not change during epinephrine infusion. Chest pain, which was not different in quality, intensity, or location from the patientʹs habitual angina-like pain, was induced in 7 of the 8 patients, 4 of whom endured only a moderate dose of epinephrine. No ST depressions were observed. After administration of phentolamine, chest pain developed to a degree similar to that with epinephrine alone. Chest pain is induced by epinephrine infusion in patients with syndrome X. Because no signs of ischemia occurred, a hypersensitive afferent cardiac nervous system may be an important cause of chest pain.