[Paroxysmal supraventricular tachycardia with complete atrio-ventricular block or dissociation]

Recent studies have shown the high incidence of concealed Bundles of Kent in the reentry circuits of paroxysmal supraventricular tachycardia. Arguments in favour of the nodal or junctional level of reentry were observed in supraventricular tachycardia with complete atrioventricular dissociation. Two such cases under went electrophysiological investigation. In the first case, tachycardia was terminated by a complete infrahisian block. However, during atrioventricular dissociation, tachycardia could be initiated by a single atrial stimulus after an increased nodal conduction time and terminated by a single atrial stimulus or cardiac message. In the second case the supraventricular tachycardia presented with complete atrioventricular dissociation due to a retrograde ventriculo-atrial block. Atrial stimulation at progressively higher rates and premature atrial extra stimuli initiated the tachycardia but could not terminate it, so confirming the non-participation of the atrium in the reentry circuit. These two cases suggest that the ventricle (case I) and the atrium (case II) are not indispensable links in junctional or nodal reentry circuits. Case II was suggestive of a common initial pathway developing retrograde unidirectional block during tachycardia.