Contribution of head-up tilt testing and ATP testing in assessing the mechanisms of vasovagal syndrome - Preliminary results and potential therapeutic implications

Background-In patients with vasovagal syndrome, head-up tilt testing may re produce symptoms generally associated with vasodepression, Recent research suggests ATP testing identifies patients with abnormal vagal cardiac inhibi tion. This preliminary study examined the joint contribution of both tests in identifying underlying mechanisms in the general population with vasovag al syndrome. Methods and Results-Both tests were performed in random order during 1 sess ion and outside of predominant sympathetic periods in 72 patients hospitali zed for syncope (n=56) or presyncope (n=16) for whom no cardiac or extracar diac cause was found. For passive and isoproterenol-provocative tilt testin g by standard protocol, reproduction of symptoms defined a positive test. T he ATP test consisted of injecting ATP 20 mg TV at bedside, continuously mo nitoring ECG and blood pressure; a vagal cardiac pause >10 seconds defined a positive test. For most patients (64%), greater than or equal to 1 test w as positive. Of the 41 patients (57%) with a positive tilt test (either pas sive or provoked by isoproterenol), 32% had cardiac disease; none had signi ficant bradycardia (<50 bpm). Of the 8 patients (11%) with a positive ATP t est, 62% had cardiac disease; the probability of a positive result increase d with age (P=0.015), Both tests were positive in 3 patients and negative i n 26 patients; the tilt and ATP test results were uncorrelated (P=0.28). Conclusions-Results suggest tilt and ATP tests individually and jointly det ermine the mechanism of vasovagal symptoms in most patients and that vagal cardiac inhibition increases with age.