[Vagal syncope in young adults: specificity of the tilt-table test]

The head-up tilt test has been used for more than 10 years to reproduce vagal lipothymia. The criteria for a positive test and specificity are however still lacking.

Thirty male volunteers, age 18 to 35 years, with no past history of lipothymia nor any signs of hypervagotonicity at physical examination, on fasting blood samples or on exercise tests with sudden interruption and Holter recording were selected for the study. Two head-up tilt tests at 60 degrees for 45 minutes were conducted, one with no presensitivisation and the other with a bolus of isoproterenol (2, 4, 6 and 8 micrograms) starting 30 minutes after the beginning of the test. Blood pressure was measured throughout the test.

The systolic blood pressure curves showed drops of more than 30 mmHg accompanied by spontaneously resolving clinical signs in 6 of the 30 subjects during the non-sensitized tests and in 14 out of 30 during the sensitized tests. A symptomatic drop in systolic blood pressure of more than 30 mmHg compared to the moment before the malaise accompanied by clinical signs which did not resolve within 1 minute and required returning to the supine position occurred in one volunteer during a non-sensibilized test. This same type of reaction was observed in 4 volunteers during sensitized tests, three times after an isoproterenol bolus.

Taking this later manifestation as the criteria for a positive head-up tilt test, the specificity of the non-sensitized and isoproterenol-sensitized tests in the young adult are 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 history of hypervagotonicity but a positive head-up tilt test may be one day confronted with a situation generating a vagal reaction.