Irregularity of the ventricular rhythm during atrial fibrillation: Effect of slow atrioventricular nodal pathway ablation

Background: The contribution of dual atrioventricular (AV) nodal pathway ph ysiology to the irregularity of the ventricular rhythm during atrial fibril lation has not been clarified. Hypothesis: This study was performed to assess the effects of slow AV nodal pathway ablation on the irregularity of the ventricular rhythm during atri al fibrillation. Methods: Irregularity of the ventricular rhythm was quantified using analys is of heart rate variability. In 20 patients with AV nodal reentrant tachyc ardia, absolute heart rate variability during atrial fibrillation was quant ified before and after slow AV nodal pathway ablation by the standard devia tion of all NN intervals (SDNN). Relative heart rate variability was determ ined by computing the coefficient of variation, SDNN normalized for the sta ndard deviation of the mean ventricular cycle length (MVCL-AF). Results: The slope of the regression between MVCL-AF and SDNN was significa ntly more gradual after slow pathway ablation (slope 0.39 vs. 0.23, p < 0.0 01). Coefficient of variation increased in 12 patients with heart rates > 1 20 beats/min at baseline (18.6 +/- 3.9 vs. 22.1 +/- 2.7% MVCL-AF, p < 0.05) , but decreased in 8 patients with heart rates < 120 beats/min at baseline (25.6 +/- 3.1 vs. 22.2 +/- 2.2% MVCL-AF; p = 0.05). Furthermore, coefficien t of variation correlated with MVCL-AF only at baseline (slope 0.034, r = 0 .66), but no relation was found after slow pathway ablation (slope 0, r = 0 ). Conclusions: Slow AV nodal pathway ablation alters the relation between abs olute heart rate variability and mean ventricular rate during atrial fibril lation and eliminates cycle length dependency of relative heart rate variab ility. These data indicate that dual AV nodal pathway physiology contribute s to the irregularity of the ventricular rhythm during atrial fibrillation.