91CLINICAL CHARACTERISTICS OF PATIENTS WITH POSITIVE VERSUS NEGATIVE ADENOSINE TESTS IN UNEXPLAINED SYNCOPE

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Abstract

Introduction: Adenosine testing has been used in the diagnosis of neurally-mediated and unexplained syncope. A positive test is adenosine induced asystole for ≥6 s or AV block ≥10 s. No prior studies have examined adenosine testing early in the syncope journey or presented data on negative adenosine tests. The appropriateness of pacing those with a positive test remains uncertain.

Methods: Adenosine testing to DEtermine the need for Pacing Therapy with the additional use of an implantable loop recorder (ADEPT-ILR) is a randomised double blind placebo controlled trial of permanent pacing following a positive adenosine test. Those with a negative test undergo ILR insertion. Patients are >40 years presenting to acute medical services with unexplained syncope (no diagnosis following history, examination, 12 lead ECG and postural BP). The pacemaker is switched “on” or “off” for 6 months and then switched to the other mode for another 6 months. Those with an ILR are followed for 12 months.

Results: 36 adenosine tests have been conducted. There have been 24 positive (67%) and 12 (33%) negative tests. Those with a positive test are older and have a longer and have a longer QTc calculated by automated report (p < 0.05; see table).

Conclusion: Adenosine testing has never been studied in this population. Two thirds of adenosine tests in unexplained syncope are positive. Those with positive adenosine tests are older and have a longer QTc.

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