title: Lack of evidence for alpha-adrenergic receptor-mediated mechanisms in the genesis of ischemia in syndrome X.
abstract: Patients with syndrome X (typical angina pectoris, positive exercise tests [greater than or equal to 1 mm of ST-segment depression], no evidence of coronary spasm and angiographically normal coronary arteries) have a reduced coronary flow reserve due to inappropriate dilatation of small resistive vessels. To assess whether alpha-adrenergic mechanisms play a role in the genesis of ST-ischemic changes in syndrome X, 12 patients with this syndrome (2 men and 10 women, mean age 50 +/- 6 years) underwent exercise testing and 24-hour ambulatory electrocardiographic monitoring. They were done off treatment and after alpha blockade with prazosin and clonidine on 2 separate weeks. Despite treatment, all exercise tests remained positive and patients were stopped because of progressive angina pain. Compared to the off-treatment tests, exercise duration and heart rate-blood pressure product at 1 mm of ST-segment depression did not change significantly after prazosin (617 +/- 203 vs 663 +/- 203 seconds and 23,857 +/- 6,125 vs 22,098 +/- 4,816 beats/min X mm Hg, respectively) and clonidine (684 +/- 148 vs 649 +/- 80 seconds and 25,514 +/- 2,386 vs 24,567 +/- 2,001 beats/min X mm Hg, respectively). Ambulatory monitoring showed similar results regarding number of episodes of ST-segment depression greater than or equal to 0.1 mV during control and after prazosin (39 vs 38) or clonidine (26 vs 23) treatment. None of the 8 patients who also underwent provocative testing with phenylephrine had ischemic electrocardiographic changes; only 2 experienced chest pain during the test.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Cardiovascular Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
authors.forename: A R
authors.initials: AR
authors.lastname: Galassi
authors.forename: J C
authors.initials: JC
authors.lastname: Kaski
authors.forename: G
authors.initials: G
authors.lastname: Pupita
authors.forename: M
authors.initials: M
authors.lastname: Vejar
authors.forename: F
authors.initials: F
authors.lastname: Crea
authors.forename: A
authors.initials: A
authors.lastname: Maseri
mesh_terms: D000328:Adult; D000787:Angina Pectoris / Q000209:etiology*; D003000:Clonidine; D017023:Coronary Angiography; D003327:Coronary Disease / Q000175:diagnosis; D004562:Electrocardiography; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010656:Phenylephrine; D011224:Prazosin; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013577:Syndrome
chemical_list: D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D003000:Clonidine; D011224:Prazosin