Analysis of randomness of atrial and ventricular rhythm in atrial fibrillation.

The aim of the present study was to examine the relationship between randomness of atrial and ventricular rhythm during atrial fibrillation. Atrial fibrillation was induced in 10 open-chest pigs by application of metacholine on the surface of the right atrium followed by incremental pacing. Local atrial rhythm (AA intervals) was recorded with a bipolar epicardial electrode, and episodes of atrial fibrillation corresponding to 500 ventricular (RR) intervals were selected for analysis. Randomness of the distribution of AA and RR intervals was assessed by autocorrelation. Pearson's test was used for statistical analysis. Random AA and RR interval distribution was observed in nine pigs (P > or = 0.05). In the remaining pig, atrial fibrillation had changed to atrial tachycardia. This was associated with immediate transition of a random to a non-random ventricular rhythm. These findings provide strong circumstantial evidence in support of the contention that randomness of ventricular rhythm during atrial fibrillation is due to randomness of atrial rhythm.