HEART-RATE-VARIABILITY AND VAGAL SYNCOPE IN THE YOUNG-ADULT

Heart rate variability is a sign of sympathetic activity. The authors compared two study populations of young males aged 19 to 30 years : po pulation T comprised 15 healthy volunteers who had two negative tilt t ests, one under basal conditions and the other after a bolus of isopro terenol : population S comprised 12 patients without cardiac or other disease, who were followed up for malaise and in whom the basal tilt t est was positive, confirming the vagal origin of syncope. Temporal and spectral (total power, low frequency 0.04 -0.15 Hz, hight frequency 0 .16 -0.40 Hz) data was obtained concerning heart rate variability from 24 hour Holter monitoring. The main difference between the two study populations was in the temporal data over 24 hours especially with res pect to the heart rate (T = 73.5 +/- 6.9; S = 65.4 +/- 6.2/min : p = 0 .004) and the percentage of successive R -R intervals varying by more than SO ms (PNN 50) (T = 20.2 +/- 8.3 % : S = 30.7 +/- 10.2 %; p = 0.0 24). At: night, the lowest SDANN/5 (standard deviation of RR intervals over periods of S minutes) were observed in group S (67.2 +/- 16.7 ms vs 87.3 +/- 24.4 ms; p = 0.026). No statistically significant differe nces between the two groups was observed in the spectral data. The tem poral data of heart rate variability on Holter ECG monitoring over 24 hours could therefore have a good predictive value of the vagal origin of syncope in young adults.