Key takeaways:A study of 150 patients with atrial fibrillation found that sleep apnea alters heart rate variability more during wakefulness than during sleep. The findings suggest that daytime monitoring and optimally timed medications could improve atrial fibrillation care for patients with sleep apnea. Using CPAP therapy improved patients’ sleep apnea and normalized overall heart rate variability. The researchers expected heart rate variability to be more abnormal while people were sleeping, when sleep apnea occurs. After using a CPAP machine, patients’ sleep apnea improved, and overall heart rate variability became more normal.