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 μg and increased in 2-μg steps to a maximum of 8 μg at 0 ° and +60 °. The responses at 0 ° were all normal. At +60 ° a vasodepressor reaction consisting of syncope or near syncope, hypotension and bradycardia was produced by isoproterenol (mean dose 6.0 ± 0.26 μg) 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 isoproterenolinduced 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.