ENZYME-HISTOCHEMICAL STUDY OF THE ATRIOVE NTRICULAR JUNCTIONAL AREA -CORRELATIONS WITH SLOW AND FAST ATRIAL PATHWAYS

It was traditionally admitted that junctional tachycardia was based on an intranodal reentry pathway. However, lesions created at a distance from the atrioventricular node by surgery or other physical means (fu lguration or radiofrequency energy ablation) demonstrated that the ree ntry circuit could use the slow and fast atrial pathways. This study p erformed in 6 human hearts less than 1 hour after death was undertaken to perform enzyme histochemical analysis of the atrial pre-nodal regi on. The specimens were rapidly frozen in liquid nitrogen and sliced wi th a cryostat. After localisation of the different regions by routine staining methods, histochemical reactions were performed using the sem i-permeable membrane method for weakly bound enzyme. Ten enzymes were studied covering the principal metabolic pathways. Though routine hist ological stain did not show any particular structures, the enzyme hist ochemical reactions showed a band of myocardium following the septal i nsertion of the tricuspid valve, joining the orifice of the coronary s inus to the posterior part of the compact atrioventricular node. This zone of myocardium had an enzymatic make-up similar to that of the sin us node. An analogous structure was also observed above the insertion of the anterior mitral leaflet. These two regions could constitute the trajectory of die slow conduction pathways.