Abstract 635: The Proximal AV Bundle in the Human Heart and Related Morbidity

Abstract

INTRODUCTION: The proximal AV bundle (PAVB) has been shown to be the only input to the AV node (AVN) in the canine heart in anatomoelectrical reports over the past 20 years. The anatomic studies utilized photographic correlations of epi- and endocardial aspects of whole hearts through blocking, and serial histologic parallel, perpendicular and transverse plane Goldner Trichrome stained sections of the flattened heart; Karnovsky’s fixative at pH 7.2 and sucrose buffer rinses; direct 3D and stereotaxic analysis. Electrical studies, under direct observation of in-vitro superfused hearts, delineated unique wire, catheter, and micropipet electrode potentials via high K, transections, Lucifer Yellow iontophoresis and photoablations during spontaneous and paced SA node rhythms and with simultaneous SA node, atrionodal bundles, PAVB, AVN and distal AV bundle recordings. HYPOTHESIS: The PAVB exists in the human heart. METHODS AND RESULTS: Explanted normal human hearts, deemed unsuitable for transplantation, processed as above with transverse sections, revealed that the AVN (Figs. A–C ) is joined by the PAVB at a 90-degree angle (Figs. B, C ). These “normal” hearts from older patients (57– 80 yr) had atrophic or absent atrial myocardium. In Figure C , most of the right medial atrial wall myocardium, but not the left atrium (LA), had been replaced by fat. CONCLUSIONS: PAVB is the only AVN input in the human heart. As in the canine heart, PAVB also runs away from the annulus and is apposed to LA. Knowledge of the PAVB should be helpful in decreasing morbidity associated with clinical procedures. Care must be taken in ablating the fast superior atrionodal bundle pathway input to the PAVB. Figures A and B are from the same 60 yr and C is from a 71 yr old heart. AVN (A) is apposed to the left ventricular outflow tract (LVOFT and dotted line) along with the PAVB ( B and C ). But as seen in C , PAVB assumes a position apposed to LA, And, as in the dog heart, thereafter (not shown here) PAVB is completely apposed to LA.