Paroxysmal supraventricular tachycardia caused by 1 : 2 atrioventricular conduction in the presence of dual atrioventricular nodal pathways

One-to-two atrioventricular conduction, ie, the double response to a single sinus or atrial impulse, resulting in two QRS complexes for one P wave, is a rare manifestation of dual atrioventricular (AV) nodal pathways. This re port describes the case of a 61-year-old woman with continuous episodes of supraventricular tachycardia caused by independent conduction to the ventri cles of sinus impulses over both the fast and the slow AV nodal pathway, gi ving rise to a ventricular rate that was twice the sinus rate. A wide spect rum of electrocardiographic manifestations of 1:2 AV conduction was observe d on the surface electrocardiogram. The diagnosis was suggested by several elements including evidence of dual AV nodal pathways during sinus rhythm a nd cycle length alternans during tachycardia. The patient underwent success ful slow pathway ablation with complete disappearance of symptoms and elect rocardiographic manifestations of 1.2 AV conduction,