Exacerbation of Vasodepressor Syncope by Beta-Adrenergic Blockade

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Abstract
The tilt test has been used to elicit a vasovagal—vasodepressor reaction in patients with unexplained syncope.1 , 2 The mechanism is not clear. It has been postulated that in the head-up position, venous pooling in the lower limbs reduces ventricular volume and raises sympathetic activity; this causes vigorous myocardial contraction and stimulates the ventricular mechanoreceptor, which results in reflex sympathetic inhibition.1 2 3 4 Sympathetic hyperreactivity is thought to play an integral part in vasodepressor syncope; thus, beta-agonists have been used to provoke this reaction2 , 5 and beta-antagonists to prevent it.5 , 6 Recently, we had an opportunity to study a patient with typical vasodepressor syncope and found that her symptoms were exacerbated by a beta-adrenergic blocking agent.