ANISOTROPIC CONDUCTION IN THE TRIANGLE OF KOCH OF MAMMALIAN HEARTS - ELECTROPHYSIOLOGIC AND ANATOMIC CORRELATIONS

Objectives, The purpose of this study was to characterize anisotropy i n the triangle of Koch by relating electrophysiology with anatomy, Bac kground. Atrioventricular (AV) node fast and slow pathway characterist ics have been suggested to be due to nonuniform anisotropy in the tria ngle of Koch,Methods, During atrial pacing, we determined the electric al activity within the triangle of Koch by multichannel mapping in 11 isolated hearts from pigs and dogs, Orientation of fibers was determin ed in nine hearts, Results, Fibers were parallel to the tricuspid valv e annulus (TVA) in the posterior part of the triangle of Koch, In the midjunctional area, the direction of the fibers changed to an orientat ion perpendicular to the TVA, During stimulation from posterior and an terior sites, activation proceeded parallel to the TVA at a high condu ction velocity (0.5 to 0.6 m/s), During stimulation from sites near th e coronary sinus, a narrow zone of slow conduction occurred in the pos terior part of the triangle of Koch where activation proceeded perpend icular to the fiber orientation, Above and below this zone, conduction was fast and parallel to the annulus, After premature stimulation, co nduction delay in the triangle of Koch increased by 4 to 21 ms; in con trast, the AH interval increased by 80 to 210 ms, Conclusions, Data su pport the concept of anisotropic conduction in the triangle of Koch, A ctivation maps correlated well with the arrangement of superficial atr ial fibers, Comparison of conduction delay in the triangle of Koch and AH delay after premature stimulation disproves that anisotropy in the superficial layers plays an important role in slow AV conduction. (C) 1998 by the American College of Cardiology.