SLOW POTENTIALS IN THE ATRIOVENTRICULAR JUNCTIONAL AREA OF PATIENTS OPERATED ON FOR ATRIOVENTRICULAR NODE TACHYCARDIAS AND IN ISOLATED PORCINE HEARTS

Objectives. The purpose of this study was to 1) investigate extracellu lar electrograms in the atrioventricular (AV) junctional area of patie nts with AV node reentrant tachycardia, 2) compare them with recording s made in isolated porcine hearts, and 3) study their origin. Backgrou nd. Electrograms with slow components have been use to to target the d elivery of radiofrequency energy for the cure of AV node reentrant tac hycardia. The origin of these electrograms is unknown. Methods. In 12 human and 19 porcine hearts, extracellular recordings were made simult aneously from 64 sites. In five other porcine hearts, intracellular re cordings were made at sites at which extracellular electrograms reveal ed slow potentials. Histologic investigations were carried out in four of these hearts.Results. Electrograms with slow components were recor ded in five human and eight porcine hearts. These signals were found a t sites up to 12 mm from the His bundle. Characteristics of the electr ograms did not differ significantly among human and porcine hearts. El ectrophysiologic evidence for multiple pathways was present in four he arts. Superficial impalements with micro- electrodes at sites with slo w potentials showed action potentials with AV node characteristics. In the majority of these recordings, the upstroke coincided with the dow nstroke of slow potentials. Histologic investigations of the sites of impalement revealed transitional cells directly underneath the endocar dium. Conclusions. Slow potentials were recorded in bath human and por cine hearts in similar measure. They arise from transitional cells and have action potentials similar to N cells.