The effect of atropine in vasovagal syncope induced by head-up tilt testing

This single-blinded, randomized, placebo-controlled study was designed and undertaken to assess the efficacy of intravenous atropine administration on haemodynamic impairment induced by head-up tilt testing in patients with vasovagal syncope.

One hundred and thirteen consecutive patients (62 male and 51 female, mean age 46.3 years) with recurrent syncope, no evidence of cardiac, neurological or metabolic disease and a positive head-up tilt test were included in the study. Within 2 weeks of the first head-up tilt test all patients underwent a second tilt test. During this second test, all patients were randomized to receive a bolus of either atropine (0.02 mg. kg(-1)) or placebo (isotonic saline solution). The administration of atropine or placebo was performed at the onset of the haemodynamic modifications (heart rate and/or blood pressure fall) in conjunction with typical vasovagal prodromal symptoms. Treatment was taken as effective when symptoms aborted and the test was completed. In 29 of 113 patients the second tilt test was negative and these patients were excluded from final data analysis. Forty-one patients received placebo, which was effective in nine cases (21.9%). Atropine was administered to 43 patients and was effective in 30 cases (69.7%, P<0.01 vs placebo). The effects of treatment were analysed further to consider the haemodynamic patterns of tilt-induced vasovagal reflex. In the cardio-inhibitory form, placebo was never effective (15 cases), while atropine was effective in 15 of 18 cases (83.3%, P<0.001 vs placebo). In the vasodepressor form, placebo was effective in nine of 26 patients (34.6%), while atropine was effective in 15 of 25 cases (60.0%, no significant difference vs placebo).

Atropine is fully effective in the cardio-inhibitory form of tilt-induced vasovagal reflex, but is limited in the vasodepressor form.