P6573Adenosine plasma levels may determine tilt table test outcome in syncopal patients with prodromal symptoms

Abstract

Abstract Background/Introduction Head-up tilt table test (HUTT) and Adenosine test (ADT) are tools frequently used in the diagnostic workup of syncope. It has been suggested that patient responses to HUTT and ADT can be related to the plasma levels of Adenosine (ADPL) and Adenosine receptors (ADR). However, the exact type of association and the role of (ADPL) and ADR levels in the risk stratification and management of patients with syncope has not yet been clarified. Purpose We sought to assess the ADPL and ADR levels in patients without structural heart disease who underwent HUTT and ADT tests as part of the diagnostic workup of syncope. We specifically investigated differences with regards to the presence of a history of prodromal symptoms. Methods HUTT and ADT were performed as per the standard protocols. ADT was considered positive in the event of asystole >6 seconds or heart block for >10 seconds after intravenous Adenosine administration in a supine position at a dose of 0.15 mg/kg. ADPL were assessed at three timepoints during the HUTT: in the supine position, immediately after bed tilt and, in cases of a positive test, at the time of syncope. Furthermore, we assessed the A2A ADR of monocytes in the study patients. Results We prospectively analyzed 77 patients (48 women, age 47.05±21.10 years). ADT was positive in 16.7% of patients and HUTT in 49.4% of patients. ADPL in the supine position did not differ between patients with negative vs. positive ADT but showed a significant correlation with the body mass index (p=0.002). There was a trend for reduced ADPL at the tilt phase in patients with positive HUTT (0.32±0.89 vs. 0.42±0.77 ppm/Um/L, p=0.09). Of all patients, 60 (77.9%, 41 women, age 46.80±21.83 years) had reported a history of prodromal symptoms at syncope. In the subset of patients with prodromal symptoms, the ADL at the tilt phase were lower in patients with positive vs. negative HUTT (0.15±0.23 vs. 0.51±0.89, p<0.05). ADR did not differ among groups but showed a significant correlation with the ADL during syncope in patients with prodromal symptoms (p<0.05). Conclusion(s) Patients with prodromal symptoms and a positive HUTT demonstrate reduced ADPL at the tilt phase of HUTT preceding syncope. In these patients, ADPL in syncope correlate with the ADR. Adenosine plasma levels and receptors warrant further investigation and may predict the response to HUTT thereby contributing to the diagnostic evaluation and risk stratification of patients with syncope.