VAGAL SYNCOPE IN THE YOUNG-ADULT - SPECIF ICITY OF THE HEAD-UP TILT TEST

Objective: The head-up tilt test has been used for more than 10 years to reproduce vagal Lipothymia. The criteria for a positive test and sp ecificity are however still lacking. Method: Thirty male volunteers, a ge 18 to 35 years, with no past history of lipothymia nor any signs of hypervagotonicity at physical examination, on fasting blood samples o r on exercise tests with sudden interruption and Bolter recording were selected for the study, Two head-up tilt tests at 60 degrees for 45 m inutes were conducted, one with no presensitivisation and the other wi th a bolus of isoproterenol (2, 4, 6 and 8 mu g) starting 30 minutes a fter the beginning of the test, Blood pressure was measured throughout the test. Results: The systolic blood pressure curves showed drops of more than 30 mmHg accompanied by spontaneously resolving clinical sig ns in 6 of the 30 subjects during the non-sensitized tests and in 14 o ut of 30 during the sensitized tests. A symptomatic drop in systolic b lood pressure of more than 30 mmHg compared to the moment before the m alaise accompanied by clinical signs which did not resolve within 1 mi nute and required returning to the supine position occurred in one vol unteer during a non-sensibilized test. This same type of reaction was observed in 4 volunteers during sensitized tests, three times after an isoproterenol bolus. Conclusion: Taking this later manifestation as t he criteria for a positive head-up tilt test, the specificity of the n on-sensitized and isoproterenol-sensitized tests in the young adult ar e 96.7 and 86.7% respectively, These findings must be considered with caution since there is no proof that these young men with no past hist ory of hypervagotonicity but a positive head-up tilt test may be one d ay confronted with a situation generating a vagal reaction.