Background: Selection of treatment in vasovagal syndrome should be guided by the mechanism of symptoms. This study determined whether a simple drug test may assess one mechanism. Methods and Results: To identify patients at risk of severe cardioinhibitory response of vagal origin, we infused 20 mg ATP into 316 patients hospitalized for recurrent syncope (n=195) or presyncope (n=121) of unknown origin and into normal subjects (n=51). We then assessed the ECG and clinical responses to the drug, recommended therapy, and followed up the subjects chronically. A cardiac pause >10 seconds was seen in only 3 normal subjects (6%). Therefore, a pause ≤10 seconds yielded the ≃95th percentile of the normal range. ATP provoked a pause >10 seconds in 130 symptomatic patients (41%) and a pause ≤10 seconds in 186 symptomatic patients (59%). Thus, symptomatic patients with pauses >10 seconds were proposed for pacemaker implantation; all other patients and normal subjects were simply monitored. Among long-pause patients with follow-up, the observed recurrence rate for the 104 with pacemakers was one-third that for the 21 who were only monitored (P<.0001). Among followed-up short-pause patients, the rate in the 153 monitored-only patients did not differ from the 20 implanted patients (P=.432). Conclusions: The vagal effect of ATP may identify the subgroup of patients at high risk of severe cardioinhibitory response of vagal origin who likely will benefit from pacemaker therapy. This fast, uncomplicated test should be considered for further use in screening patients with vasovagal syndrome.
- Vagus nerve