Aims: To assess the involvement of sleep apnoea in nocturnal sudden cardiac death (SCD) by evaluating cardiac electrical instability using T-wave alternans (TWA), a risk marker for lethal cardiac arrhythmias, and severity of sleep apnoea in congestive heart failure (CHF) patients.
Methods and results: A total of 40 CHF patients simultaneously underwent overnight simplified respiratory polygraphy and 24 h continuous electrocardiography. Peak TWA during both daytime and nighttime were calculated by the modified moving average method. The patients were divided into two groups; 30 patients with daytime predominant TWA (whose peak TWA was higher during daytime than during nighttime) and 10 with nighttime predominant. Apnoea-hypopnoea index (AHI) was significantly higher in patients with nighttime predominant TWA than in those with daytime predominant (35.9 +/- 8.1 vs. 23.9 +/- 14.4 events/h, P = 0.02), and was an independent predictor of nighttime predominant TWA (odds ratio, 1.08; 95% confidence interval, 1.01-1.16; P = 0.03). Moreover, peak TWA during the night was correlated positively with AHI (P < 0.001), and AHI was an independent determinant of nocturnal TWA value (r(2) = 0.27, P = 0.009).
Conclusion: In CHF patients, sleep apnoea induces cardiac electrical instability manifested as TWA, reflecting increased risk of nocturnal SCD. Moreover, some CHF patients with sleep apnoea exhibit nighttime predominant TWA. Therefore, TWA should also be evaluated during the night.