Extra-and intracellular recordings from the AV junction: discerning the mechanisms for irregular ventricular responses during supraventricular arrhythmias

Abstract

Introduction There has been a long-standing controversy regarding the mechanism(s) to explain the irregular ventricular response during atrial tachycardia (AT) or atrial fi brillation (AF) and where the site of block, if any, resides in the atrioventricular (AV) junction.Methods We studied 12 Langendorff preparations perfused with modifi ed Tyrode’s solution containing 5-10 mM diacetyl monoxime which suppressed contractility but allowed the use of intracellular action potential (AP) recordings. Octapolar catheters (2-mm rings, 2-mm spacing) were secured along the tricuspid annulus from the apex to the base of the triangle of Koch and along the anterior limbus of the fossa ovalis to record extracellular, slow pathway, fast pathway, His bundle (Hb) and AV nodal (AVN) extracellular potentials as well as intracellular action potentials.Results AT or AF induced by rapid atrial pacing showed a variety of irregular responses due to: (1) Wenckebach conduction showing decrement within the AVN and progressive diminution of extracellular AVN potentials (n = 5); (2) repetitive concealed conduction proximal to the AVN (n = 3); (3) ectopic beats arising within the AVN (n = 2); (4) ectopic beats arising at the Hb (n = 2).Conclusions In this experimental preparation, extracellular and intracellular recordings provided presumptive evidence for the mechanisms causing the irregularities of the ventricular response such as repetitive concealed conduction, enhanced automaticity or electrotonically triggered activity. Also more defi nitive determinations of the site of block in the AV junction were also obtained.