Is respiratory sinus arrhythmia present in atrial fibrillation? A study using two quantitative methods.

Two quantitative techniques have been evaluated to examine whether respiratory sinus arrhythmia can be detected in atrial fibrillation. Cyclical changes in heart rate during deep breathing indicating respiratory sinus arrhythmia were seen in 11/15 control patients, but only 1/44 patients with atrial fibrillation. Power spectrum analysis suggested that more subtle variations in heart rate with breathing may be present in some patients with atrial fibrillation where it was not detectable by simpler techniques. These results support the hypothesis that although respiratory sinus arrhythmia is not detectable in atrial fibrillation by conventional means, there may still be some mediation of heart rate either by vagal or extravagal mechanisms.