Overnight T-wave alternans in sleep apnea patients

Sleep apnea (SA) is linked to cardiovascular complications and to an increased risk of sudden cardiac death. Microvolt T-wave alternans (TWA) is a noninvasive electrocardiographic (ECG) index of cardiovascular risk; its rate of occurrence in SA patients remains unknown. Thus, this study investigated the occurrence of TWA in SA patients during night. To this aim, overnight ECG recordings of 16 SA patients were analyzed for TWA identification by means of our heart rate adaptive match filter. Results indicate that overnight TWA was characterized by a low mean amplitude (mean TWA: 6±3 µV). However, higher-amplitude transient TWA episodes (max TWA: 29±21 µV) occurred overnight, sometimes when patients were awake (max TWA: 33±18 µV; 56% of cases) and sometimes when patients were sleeping (max TWA: 24±23 µV; 44% of cases with 13%, 19%, 6% and 6% during sleep stage 1, 2, 3 and 4, respectively). In only 3 subjects (19%) TWA peaks occurred during an SA episode: during obstructive apnea with arousal in two cases (max TWA of 7 µV and 17 µV, during stages 1 and 2, respectively) and during hypoapnea with arousal in one case (max TWA of 6 µV while awake). Thus, SA patients show significant transient overnight TWA episodes, not necessarily occurring during a SA episode