A-V Nodal Tachycardia with Block

Abstract

Paroxysmal as well as nonparoxysmal varieties of rapid ectopic rhythms originating in the A-V node may be associated with various conduction disorders involving propagation of regularly generated impulses to the atria and ventricles as well as within the ventricles. This may occur following treatment of a paroxysmal tachycardia by digitalis or when impulse formation within the node becomes accelerated as a consequence of digitalis excess. Since retrograde and forward conduction may vary independently and since the tachycardia frequently develops in a presence of atrial fibrillation, actual conduction times through the A-V junction may not be measurable. The nature of the arrhythmia must be diagnosed from the spacing and characteristic grouping of ventricular and/of atrial complexes or from changes in the configuration of the ventricular beats. Several varieties of such nodal tachycardias with block are presented, including examples of (a) A-V dissociation in atrial fibrillation with Wenckebach periods of forward conduction; (b) A-V dissociation during sinus rhythm with Wenckebach periods of antegrade nodal impulses; (c) Wenckebach periods of forward conduction with constant retrograde conduction; Wenckebach periods of both forward and retrograde conduction with blocked re-entry as a possible mechanism of intermittence of the tachycardia; (e) complete and incomplete A-V dissociation due to acceleration of two nodal pacemakers; and (f) aberrant ventricular conduction simulating ventricular premature beats or resulting in a bidirectional type of tachycardia.