ORIGIN OF HEAT-INDUCED ACCELERATED JUNCTIONAL RHYTHM

Accelerated Junctional Rhythm. Introduction: The application of high-f requency current to the AV junctional area results in a temperature ri se in the myocardium and may cause accelerated junctional rhythm (AJR) , The aim of the study was to characterize heat-induced AJR in an in v itro animal model. Methods and Results: Studies were performed in isol ated perfused pig and rabbit-hearts, Using a small heating probe, we c ould induce AJR from a discrete area located in the middle of the tria ngle of Koch, which was smaller than the area from which RF energy app lication could elicit AJR, Histology showed that the heat-sensitive ar ea was located over, or close-to, the compact AV node. It did not corr espond with the areas where double potentials were found or with the s ite(s) of earliest atrial activation during VA conduction. Microelectr ode recordings revealed that AJR arose in nodal-type cells. Heat incre ased the slope of the phase 4 depolarization and shortened the action potential duration, Two types of AJR were observed: the first one was regular and the second one showed irregularity in the intervals. Inter action of multiple foci and the presence of conduction block between t he foci and the His bundle caused the irregularity of the His-His inte rvals during the second type of AJR. Conclusion: AJR observed during h eat and RF application in the AV nodal area results from the effect of heat on AV nodal cells with underlying pacemaker activity. The heat-s ensitive area is located over, or very close to, the compact AV node.