Differentiating between patients with vasovagal syncope using the analysis of heart rate variability during head-up tilt test

The aim of this paper is to improve the physiological understanding in order to differentiate between the two types of vasovagal syncope by performing a Head-up Tilt Test. The Head-up Tilt Test is a well known procedure to reproduce vasovagal syncope, patients who had syncope during the test show different orthostatic response depending on they are cardioinhibitory or vasodepressor patients which can be explain by different pathogeneses, although existing knowledge of the autonomic balance in patients with positive response is still not completely clear. The Electrocardiogram signal from 20 patients, 12 cardioinhibitory and 8 vasodepressor were analyzed with the validated software Segmenta (Laboratory of Signal and Image Processing, Rennes) to extract classical heart rate variability parameters then comparison were made within and between group for 5 minutes of resting, the first 5 minutes of the tilt test and the last 5 minutes before syncope. The Results show that Cardioinhibitory patients had higher low frequency parameter in the last 5 minutes before syncope than vasodepressor patients (p<0.05), using Principal Component Analysis, differentiating between cardioinhibitor and vasodepressor group can be done in the 5 minutes of resting and the last 5 minutes before syncope. This study suggests a lack of sympatho-vagal balance activation in subjects with vasovagal syncope which can be explained by attenuation in cardiac rhythm regulation and predominance sympathetic activity for cardioinhibitory patients. In addition we demonstrated that by using one parameter (Low Frequency), we can distinguish between the two types before five minutes of syncope but by a combination of multiple parameters using principal component analysis we can differentiate the two groups from the five minutes of supine position.