Concealed extrasystoles causing pseudo AV block can originate below the bifurcation of the His bundle in patients with distal conduction system disease.
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Concealed left bundle ectopy may cause pseudo-AV block in distal conduction disease; case reports leave open its prevalence and diagnostic implications.
In the majority of the reported cases where concealed extrasystoles caused pseudo A V block, impulse formation occurred above the so-called bifurcation of the His bundle. The two patients reported in this communication, however, showed manifest and concealed ectopic impulses originating in the left bundle-branch or its posteroinferior division. Both had prolonged HV intervals which were attributed to organic disease of the distal ventricular specialized conducting system. The ectopic beats remained confined to the two major com- partments of the A V conducting system, namely A V nodal and ventricular specialized. Thus, for the purposes of concealment the A V junction extended from the atrial pre-A V nodal regions to the peripheral (physiological) ventricular 'gates'.
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Castellanos et al. (1974) studied this question.
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