Bimodal RR interval distribution in chronic atrial fibrillation: Impact ofdual atrioventricular nodal physiology on long-term rate control after catheter ablation of the posterior atrionodal input

Bimodal RR Interval Distribution. Introduction: Radiofrequency (RF) cathete r modification of the AV node in patients with atrial fibrillation (AF) is limited by an unpredictable decrease of the ventricular rate and a high inc idence of permanent AV block. A bimodal RR histogram has been suggested to serve as a predictor for successful outcome but the corresponding AV node p roperties have never been characterized. We hypothesized that a bimodal his togram indicates dual AV nodal physiology and predicts a better outcome aft er AV node modification in chronic AF, Methods and Results: Thirty-seven patients were prospectively subdivided in to two groups according to the RR histogram of 24-hour ECG monitoring. Befo re to RF ablation, internal cardioversion and programmed stimulation were p erformed. Among the 22 patients (group I) with a bimodal RR histogram, dual AV nodal physiology was found in 17 (77%) patients, Ablation significantly decreased ventricular rate with loss of the peak of short RR cycles after ablation (mean and maximal ventricular rates: 32% and 35% rate reduction, r espectively; P < 0.01), In 15 patients with a unimodal RR histogram (group II), dual AV nodal physiology was found in 2 (13%), and rate reductions wer e 16% and 17%, respectively. At 6 months, 3 (14%) patients in group I and 6 (40%) in group II underwent elective AV nodal ablation with pacemaker impl antation due to intolerable rapid ventricular response to AF, Conclusion: Bimodal RR interval distribution during chronic AF suggests the presence of dual AV nodal physiology and predicts a better outcome of RF a blation of the posterior atrionodal input.