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(Circulation. 2002;106:569.)
© 2002 American Heart Association, Inc.

Clinical Investigation and Reports

Role of Endogenous Adenosine as a Modulator of Syncope Induced During Tilt Testing

Alain Y. Saadjian, MD; Samuel Lévy, MD; Fréderic Franceschi, MD; Ibrahim Zouher, MD; Franck Paganelli, MD; Régis P. Guieu, MD, PhD

From the Division of Cardiology (A.Y.S., S.L., F.F., F.P.), Centre Hospitalo-Universitaire Nord, Marseille, France, and the Institut National de la Santé et de la Recherche Médicale (A.Y.S.), Centre National de la Recherche Scientifique: UMR 6560 and the Department of Biochemistry (I.Z., R.P.G.), Centre Hospitalo-Universitaire Timone, Marseille, France.

Correspondence to Samuel Lévy, MD, Division of Cardiology, Hopital Nord, 13326 Marseille Cedex 15, France. E-mail levy{at}aix.pacwan.net

Background— Previous reports that used head-up tilt testing and adenosine administration have suggested that adenosine may be an important endogenous mediator that may trigger a vasovagal response in susceptible patients. However, little is known regarding endogenous adenosine plasma levels (APLs) during vasovagal syncope provoked by tilt testing. The aim of this study was to determine whether APLs differ in patients with a positive head-up tilt test compared with those with a negative test and whether APLs are modified during tilt-induced vasovagal syncope.

Methods and Results— APLs (mean±SEM) were measured during head-up tilt test in 26 patients who presented with unexplained syncope. In the 15 patients with a negative test, APLs were 0.39±0.03 µmol/L at baseline, 0.22±0.03 µmol/L immediately after tilting, and 0.44±0.03 µmol/L after 45 minutes. APLs were significantly higher in the 11 patients with a positive test (2.66±0.67 µmol/L at baseline and 3.22±0.85 µmol/L immediately after tilting) than in those with a negative test. During tilt testing–induced syncope, APLs increased to reach 4.03±0.66 µmol/L (ie, a 52% increase compared with baseline levels; P<0.02). Furthermore, we observed that the higher the APL during syncope, the shorter the time to appearance of symptoms.

Conclusions— This study showed that APLs were higher in patients with a positive tilt test than in patients with a negative test and that they increased during tilt testing–induced syncope. These observations suggest that adenosine release may be involved in the triggering mechanism of syncope induced during tilt testing.

Key Words: adenosine • syncope • tests

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