Usefulness of tilt-induced heart rate changes in the differential diagnosis of vasovagal syncope and chronic autonomic failure.

To determine whether the heart rate changes during tilt table testing could be used in the differential diagnosis between vasovagal syncope and chronic autonomic failure. We compared the relationship between electrocardiographic R-R intervals and beat-to-beat blood pressure in 43 patients with typical vasovagal responses and 30 patients with chronic autonomic failure (6 pure autonomic failure, 23 multiple system atrophy, and 1 Parkinson’s disease). In every patient with vasovagal syncope, at the time when the blood pressure was falling, it was possible to identify at least 12 successive heart beats (mean 33 ± 2 heart beat, range 12–57) when blood pressure and heart rate fell in parallel, i.e., there was a negative relationship between blood pressure and R-R intervals ( P < 0.001). In contrast, the relationship between blood pressure and R-R intervals in patients with chronic autonomic failure was never negative, i.e., heart rate always increased, albeit less than expected for the given fall in blood pressure, or remained unchanged. The heart rate changes during the fall in blood pressure can distinguish patients with vasovagal responses from those with chronic autonomic failure. [ABSTRACT FROM AUTHOR]