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(Circulation. 1973;47:543.)
© 1973 American Heart Association, Inc.

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Paradoxic Phenomenon of Premature Beats with Narrow QRS in the Presence of Bundle-Branch Block

RASHID A. MASSUMI M.D.¹; GENERAL HILLIARD M.D.¹; ANTHONY DEMARIA M.D.¹; RAMON FABREGAS M.D.¹; ALAN E. LINDSAY M.D.¹; EZRA AMSTERDAM M.D.¹; DEAN T. MASON M.D.¹

¹ From the Section of Cardiovascular Medicine, University of California School of Medicine, University of California at Davis, and the Intermountain Clinic, Salt Lake City, Utah.

In contrast to the functional bundle-branch block (BBB) which is frequently rate-related and disappears when heart rate slows, we have encountered seven cases of a paradoxic disappearance of an existing, ischemia-induced BBB in premature beats. Supernormal conduction within the blocked bundle branch was not present in any of the cases. His bundle electrography in three of the cases demonstrated His spikes before each of the narrow-QRS premature beats. The His-Q intervals of the premature beats were considerably shorter than those of the control sinus beats. This finding clearly indicated an ectopic origin midway between the ventricular myocardium and the His bundle, i.e., within the ischemic fascicles of the left bundle, or the ischemic right bundle. From their points of origin such fascicular impulses propagate antegradely toward the respective area of the ventricular myocardium, and retrogradely toward the main His bundle, and at the same time down the remaining two fascicles. The antegrade conduction time in the short pathway down the ischemic fascicle is equaled by the faster conduction through the longer pathways of the remaining, uninjured fascicles, thereby accounting for the almost simultaneous activation of the myocardium of the two ventricles and the resultant narrow-QRS complexes.

Key Words: Supernormality • Functional bundle-branch block • Paradoxic bundle-branch block • Fascicular beats

Submitted on October 28, 1972
Accepted on November 11, 1972

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