Demonstration of dual A V pathways in a patient with Lown Ganong Levine syndrome

Electrophysiologic evidence suggestive of dual A V transmission (atrium to His bundle) is presented in a patient with short P R, narrow QRS, and paroxysmal supraventricular tachycardia. A 'fast pathway', probably representing an A V nodal bypass tract (James tract) and a 'slow pathway' possibly reflecting the A V node were defined using the extrastimulus technique. The 'fast pathway' conduction time (A H) did not increase appropriately with rapid atrial pacing or with premature atrial stimulation. The 'slow pathway' showed increase in A H interval, with shortening of the atrial coupling interval. The 'fast pathway' effective refractory period was longer than the 'slow pathway's'. The echo zone coincided with A₁ A₂ equal or less than the 'fast pathway' effective refractory period.