Lidocaine and His Bundle Extrasystoles

Abstract

Concealed discharge from the bundle of His was first postulated by Langendorf and Mehlman in 1947¹to explain an unusual case of first- and second-degree atrioventricular (AV) block associated with junctional extrasystoles. Twenty-three years later, Rosen et al²demonstrated the presence of concealed His bundle extrasystoles, and several subsequent reports have confirmed the observation.^3-8 We present here another case demonstrating periods of PR prolongation and second-degree AV block mimicking types I and II, which resulted from concealed His bundle extrasystoles. The His bundle extrasystoles in this patient neither were coupled by a fixed interval to the previous QRS nor were they parasystolic; the His bundle extrasystoles either conducted normally, conducted with functional right bundle-branch block or functional left bundle-branch block, or blocked entirely, depending on the preceding cycle length and the coupling interval. These events afforded us a unique opportunity to study the effects of lidocaine on