title: Isoproterenol induction of vasodepressor-type reaction in vasodepressor-prone persons.
abstract: The ability of isoproterenol to induce symptoms and laboratory findings of a vasodepressor reaction was tested in 48 patients, ages 17 to 74, divided into 4 groups according to the reason for their referral. Group 1 comprised 12 patients with vasodepressor syncope, group 2 had 8 patients with syncope of unknown origin, group 3 included 11 patients with syncope due to seizures in 2 and ventricular tachycardia in 9, group 4 had 17 patients with various arrhythmias not associated with syncope. Isoproterenol boluses were administered starting at 2 micrograms and increased in 2-micrograms steps to a maximum of 8 micrograms at 0 degree and +60 degrees. The responses at 0 degrees were all normal. At +60 degrees a vasodepressor reaction consisting of syncope or near syncope, hypotension and bradycardia was produced by isoproterenol (mean dose 6.0 +/- 0.26 micrograms) in 8 patients from group 1 (66.6%), 4 from group 2 (50%), 0 from group 3 and 4 from group 4 (23.5%). Three of the 4 patients in group 4 had a remote history of classic vasodepressor syncope. The overall sensitivity and specificity of the test were 73 and 85%, respectively, while the predictive accuracy of a test with positive or negative outcome were 69 and 89%, respectively. Muscarinic receptor blockade with atropine in 4 patients prevented isoproterenol-induced bradycardia but not hypotension or symptoms of fainting. Beta-adrenergic receptor blockade with propranolol inhibited all aspects of the isoproterenol-induced faint. Thus, the administration of isoproterenol during a passive upright tilt may identify persons who suffer from or are prone to a vasodepressor reaction.
authors.affiliation: Department of Medicine, University of Toronto, Ontario, Canada.
authors.forename: M B
authors.initials: MB
authors.lastname: Waxman
authors.forename: L
authors.initials: L
authors.lastname: Yao
authors.forename: D A
authors.initials: DA
authors.lastname: Cameron
authors.forename: R W
authors.initials: RW
authors.lastname: Wald
authors.forename: J
authors.initials: J
authors.lastname: Roseman
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007545:Isoproterenol; D008297:Male; D008875:Middle Aged; D011187:Posture; D013575:Syncope / Q000139:chemically induced* / Q000209:etiology; D013997:Time Factors
chemical_list: D007545:Isoproterenol