Supernormal conduction in the left bundle branch unmasked by the linking phenomenon.
This presentation reflects a case of phase-3 left bundle branch block (LBBB). Analysis reveals that relatively early QRS complexes are wide, whereas beats occurring later than a critical time are narrow. There are, however, two unexpected phenomena: (1) an overlap occurs between the range of R-R intervals resulting in normal intraventricular conduction and the range of R-R intervals resulting in LBBB pattern. Complexes that follow a wide beat are often wide although they are associated with relatively long R-R intervals, whereas complexes that follow a normal beat tend to be normal even after relatively short R-R cycles. This is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction (the so-called linking phenomenon). (2) Some early supraventricular impulses, paradoxically, resulted in normal intraventricular conduction. The phenomenon is a manifestation of supernormal LBB conduction, and only occurs following a wide QRS complex associated with retrograde activation of the LBB. The linking phenomenon reveals or unmasks the supernormal phase of LBB conduction. Following a retrograde and delayed activation of the LBB, the refractory period of the bundle branch is postponed, in such a way that a supraventricular impulse is allowed to occur during the early phase of supernormal conduction.
Luzza
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F
Istituto Pluridisciplinare di Clinica Medica-Cattedra di Malattie Cardiovascolari, Università di Messina, Italy.
Oreto
G
G
Donato
A
A
Satullo
G
G
Scimone
I M
IM
D000368:Aged; D002037:Bundle-Branch Block / Q000503:physiopathology*; D004562:Electrocardiography; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans