Electrophysiologic testing in the upright position: improved evaluation of patients with rhythm disturbances using a tilt table.

Patients are traditionally evaluated in the supine position in the electrophysiology laboratory, although symptoms due to a cardiac rhythm disturbance are often maximal clinically during standing. The assumption of the upright position results in dependent displacement of blood, followed by prompt vasoconstriction to maintain arterial pressure. This normal response may aggravate tachyarrhythmias by increasing catecholamine levels or may precipitate vasodepressor syncope if the vasoconstrictor response is absent. The use of a tilt table during electrophysiologic testing was evaluated over a 12 month period in 104 patients having a mean age of 60 years (range 37 to 81): 59 with supraventricular tachycardia, 6 with vasovagal syncope and 39 with carotid sinus hypersensitivity. Twenty-three patients (22%) had significant abnormalities when upright that were not present when supine: eight patients with supraventricular tachycardia who had their clinical syndromes of palpitation and syncope reproduced when upright, but only minimal symptoms when supine; two patients with supraventricular tachycardia who had sustained atrioventricular reentry when upright, but only two to eight beats of tachycardia when supine; six patients with syncope and a normal cardiac evaluation before electrophysiologic testing who had their typical spells only after being placed upright during a vasovagal event and seven patients with carotid sinus hypersensitivity who had their clinical syndromes reproduced with carotid sinus massage only when upright, developing hypotension despite maintaining their heart rate with sinus rhythm or pacing (vasodepressor response). In 22% of patients, electrophysiologic testing in the upright position provided clinically important information that was not evident during standard testing in the supine position.