Time-frequency analysis of the autonomic response to head-up tilt testing in Brugada syndrome

Cardiac events in Brugada syndrome (BS) usually occur at rest and mainly at nighttime, commonly relating changes in autonomic modulation to arrhythmogenesis. A major challenge today is to differentiate symptomatic and asymptomatic patients in order to optimize their therapy. Since autonomic assessment can be improved by the application of standard maneuveurs, this study analyzes and compares the autonomic response to head-up tilt (HUT) testing on 20 symptomatic and 45 asymptomatic BS patients. Their standard 12-lead ECG recordings were collected during a HUT test composed of the following three phases: (1) supine rest for 10 minutes, (2) tilting with an inclination of 60° for 45 minutes and (3) supine rest for 10 minutes. Spectral non-stationary heart rate variability indicators were extracted by means of a Smoothed Pseudo Wigner Ville distribution approach that adapts frequency bands to respiratory information. Symptomatic patients showed an increased parasympathetic tone and a reduced sympathovagal balance with respect to asymptomatic patients during tilting, and particularly before the 15th minute of the test. The results provide new insights into the autonomic function in BS, with a potential impact on the use of time-reduced HUT testing for risk stratification.