Noninvasive support for and characterization of multiple intranodal pathways in patients with mitral valve disease and atrial fibrillation

Twenty-four-hour ambulatory ECG recordings were made in 22 patients with mitral valve disease and sustained atrial fibrillation. Computer analysis was used to stratify 64-beat periods according to the average ventricular rate levels. The distribution of pooled RR-intervals from heart-rate levels 50-60, 60-70 ... 160-170 were then presented as histograms, using a 20 ms width. This heart-rate stratified analysis revealed a bi- or trimodal RR-distribution in 16 of the 22 patients. This finding was interpreted as indicating the presence of two separate atrionodal pathways and in some cases nodal escape activity in addition. A limited heart-rate range may have obscured this phenomenon in 5 of the 6 cases without signs of bimodality. At high heart rates, AV-nodal conduction occurred via a 'fast pathway' whilst at successively lower heart rates, this conduction was blocked and a 'slower pathway' was used instead. In addition, at successively slower rates, the dominant cycle of conduction via either pathway tended to lengthen according to a linear relationship. The change of dominance from the fast to the slow pathway occurred between 90 and 120 beats per minute in almost all cases. The further electrophysiological characterization of patients with 2 pathways was done by calculation of differences and ratios between lengths of dominant cycles of different pathways at the rate of change of dominance. The findings may serve as reference data for further studies of AV-nodal conduction using the same method. Furthermore, the study strongly indicates that dual AV-nodal pathways are an ubiquitous phenomenon and supports the hypothesis that even in man, AV-nodal input follows two main routes: along the crista terminals between the coronary sinus and the tricuspid valve and from the interatrial septum.