Clinical features of adenosine sensitive syncope and tilt induced vasovagal syncope

Aim-To evaluate the possible relation between adenosine sensitive syncope a nd tilt induced vasovagal syncope. Methods-An ATP test and a head up tilt test were performed in 175 consecuti ve patients with syncope of uncertain origin. The ATP test consisted of the rapid intravenous injection of 20 mg of ATP; a positive response was defin ed as the induction of a ventricular pause (maximum RR interval) greater th an or equal to 6000 ms. The head up tilt test was performed at 60 degrees f or 45 minutes; if negative, 0.4 mg oral glyceryl trinitrate spray was given and the test continued for a further 20 minutes; a positive response was d efined as induction of syncope in the presence of bradycardia, hypotension, or both. Results-Of the 121 patients with a positive response, 77 (64%) had a positi ve head up tilt alone, 18 (15%) had a positive ATP test alone, and in 26 (2 1%) both ATP and head up tilt were positive. Compared with the patients wit h isolated positive head up tilt, those with isolated positive ATP were old er (mean (SD) age, 68 (10) v 45 (20) years), had a lower median number of s yncopal episodes (2 v 3), a shorter median duration of syncopal episodes (4 v 36 months), a lower prevalence of situational, vasovagal, or triggering factors (11% v 64%), a lower prevalence of warning symptoms (44% v 71%), an d a higher prevalence of systemic hypertension (22% v 5%) and ECG abnormali ties (28% v 9%). The patients with a positive response to both tests had in termediate features. Of the 44 positive responses to the ATP test, atrioven tricular block was the cause of the ventricular pause in 43; of the 29 posi tive cardioinhibitory responses to head up tilt, sinus arrest was present i n 23 cases and atrioventricular block in six. Conclusions-ATP and head up tilt tests identify different populations of pa tients affected by syncope; these have different general clinical features, different histories of syncopal episodes, and different mechanism sites of action. Therefore, adenosine sensitive syncope and tilt induced vasovagal syncope are two distinct clinical entities.