Ventricular response to atrial fibrillation: Role of atrioventricular conduction pathways

Irregularity of the ventricular rhythm is a hallmark of patients with atrial fibrillation, yet the genesis of the irregularity is not yet fully understood. The role of the atrioventricular (AV) node in determining the irregularity of the ventricular response to atrial fibrillation was investigated by comparing the frequency distributions of the atrial (AA) and the ventricular (RR) intervals. Atrial electrograms and surface electrocardiographic leads were recorded during sustained atrial fibrillation in 12 patients with conduction over the AV node. The scaling factor (mean RR interval/mean AA interval) quantified the ability of the conduction pathway to scale the atrial input to a slower ventricular response and ranged from 2.55 to 5.92 (mean ± SD 3.77 ± 0.92). The coefficient of variation (SD/ mean) measured the relative variability of the AA and RR interval distributions. The atrial and ventricular coefficients of variation were not significantly different (0.20 ± 8.04 versus 0.21 ± 0.03, p > 0.27). Similar recordings were analyzed in six patients with conduction over an accessory AV pathway. The scaling factor ranged from 1.54 to 2.46 (2.02 ± 0.39) and, as was significantly differ (0.24 ± 0.68 versus 0,27 ± 0.10, p > 0.6). For both groups of patients, ventricular variability and the maximal RR intervals were predicted by the product of the scaling factor and either atrial variability or maximal AA intervals, respectively. This study adds direct observation of atrial events to a body of data that suggests that the irregularity of the ventricular response to atrial fibrillation is primarily a consequence of the irregularity inherent in the atrial activity. This relation was observed regardless of the nature of the AV conduction pathway, suggssting that no special properties of the AV node need to he considered to account for the irregularity of the ventricular response to atrial fibrillation.