MORPHOLOGY OF THE CARDIAC CONDUCTION SYSTEM IN PATIENTS WITH ELECTROPHYSIOLOGICALLY PROVEN DUAL ATRIOVENTRICULAR NODAL PATHWAYS

Introduction: Although the electrophysiologic criteria for dual atriov entricular nodal pathways are well established, the anatomical substra te is stilt unclear. Methods and Results: We examined the hearts from 10 patients who had been studied electrophysiologically prior to cardi ac transplantation. All 10 patients were male, aged 22 to 60 years. Ni ne of the 10 patients had dual atrioventricular nodal pathways accordi ng to accepted criteria. Histologic studies of the atrioventricular co nduction system showed normal structure of the atrioventricular node i n all 10 hearts, with minor variations within the node in 3 cases, wit hin the penetrating bundle in 3 cases, and within the nonbranching bun dle in 3 cases. The atrial approaches to the atrioventricular node wer e generally scanty in 6 hearts. The solitary case that was shown elect rophysiologically to lack dual pathways had no obvious difference in t he structure of the nodal area other than sparsity of transitional cel ls. We were unable to locate any extranodal atrial tracts as described by other investigators. Conclusion: The anatomical substrate for cond uction over dual pathways may be too subtle to be detected by gross mo rphologic studies. Since dual pathways were unmasked in all patients b ut one during electrophysiologic studies, it may be that the potential for these pathways is ubiquitous.