Paradoxical effect of respiration on ventricular rate in atrial fibrillation

1. In 50 subjects with atrial fibrillation we have attempted to demonstrate variation of ventricular rate with respiration, as evidence of cardioregulatory reflex activity. 2. The electrocardiogram was recorded for 3 min during spontaneous respiration. The presence of respiratory variation of R-R intervals was analysed by multiple regression against a cosine function (cosinor analysis), making it possible to determine the phase of respiration when the intervals were longest. 3. Variation in ventricular rate with respect to respiration was demonstrated (P < 0.05) in seven (14%) cases. On average, R-R intervals were longest at the end of inspiration; this contrasts with sinus rhythm where P-P, P-R and R-R intervals are longest around the time of end-expiration. 4. These results suggest that in atrial fibrillation the beat-to-beat ventricular rate may be under the influence of cardioregulatory reflexes, but the effect of respiration is weak and paradoxical.