Concealed discharge from the bundle of His was first postulated by Langendorf and Mehlman in 19471 to explain an unusual case of first- and second-degree atrioventricular (AV) block associated with junctional extrasystoles. Twenty-three years later, Rosen et al2 demonstrated 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
Bonner AJ, Zipes DP. Lidocaine and His Bundle Extrasystoles: His Bundle Discharge Conducted Normally, Conducted With Functional Right or Left Bundle-Branch Block, or Blocked Entirely (Concealed). Arch Intern Med. 1976;136(6):700–704. doi:10.1001/archinte.1976.03630060052011
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