INTERMITTENT PREEXCITATION AND MESOTHELIOMA OF THE ATRIOVENTRICULAR NODE - A HITHERTO UNDESCRIBED ENTITY

This is the first documented case of spontaneous intermittent preexcit ation associated with mesothelioma of the atrioventricular (AV) node, A 66-year-old male with recurrent atrial arrhythmias, palpitations, he art failure, and marked intra-atrial conduction defect that required a pacemaker died during sleep, Electrophysiologic study revealed left f ree-wail bypass tract with marked intra-atrial conduction defect and p rolonged conduction across the bypass tract, With atrial pacing, high degrees of block were noted in the bypass tract, Serial section of the conduction system and both AV rims revealed two left posterior and la teral bypass pathways with patchy areas, of fibrosis, A large mesothel ioma (benign AV nodal tumor) almost completely replaced the AV node, I n addition, there was marked fatty infiltration of the atria, In summa ry: (1) the intermittent preexcitation with prolonged conduction acros s the bypass tract and block with atrial pacing were probably related to the incomplete patchy degenerative changes in the bypass tract, and /or almost complete replacement of the AV node by the tumor; (2) the i ntra-atrial conduction defect was probably related to the replacement of the AV node by mesothelioma and/or the fatty infiltration of the at ria; and (3) the paroxysmal atrial arrhythmias probably reflect-the ma rked atrial pathology.