Ventricular Repolarization Measurement
arousals
EVENTS
In 2,558 men, a total of 407,541 arousal episodes were observed, on average 159 events (27 per hour) per participant. For every arousal, beat-to-beat RR and QT intervals were automatically extracted from the ECG channel of the PSG using our validated two-dimensional signal-warping algorithm that tracks QT changes with high precision (The 15 s prior to every arousal onset were extracted to capture the baseline characteristics in the ECG. Because the cardiac response elicited by brief sympathetic activation, such as caused by arousal, largely diminishes within 10 s, and most arousals do not exceed a few seconds, the 15 s following arousal onset were captured. To investigate the effect of arousal on repolarization in detail, we measured both QT and RR intervals beat-to-beat across three 10 s time windows: (1) baseline period, –15 to –5 s prior to arousal onset detected in the central EEG channels; (2) arousal onset, –5 s prior to arousal onset to 5 s following arousal onset; and (3) postarousal onset, 5 to 15 s following arousal onset.To quantify the ventricular repolarization dynamics prior to, during, and following arousal onset, we computed the QT variability index (QTVi):where SD