Key result
Endocardial pacing delays supernormal AV conduction, enabling consecutive conducted sinus impulses in complete heart block.
Why the study?
The concept of a supernormal phase of AV conduction had recently been challenged.
Case Report (n=1)
Demonstrates the existence of a supernormal phase of AV conduction in a patient with heart block that persists during endocardial pacing.
Answers are grounded in this paper and cite their sources.
Should not alter pacing strategies in heart block; hypothesis-generating and requires prospective validation.
A distinct, well-defined phase has been identified in a patient with heart block during which sinus impulses were conducted to the ventricles.This phase persisted during pacing but its onset and termination were delayed.No significant difference was found at varying pacing rates.On four occasions while pacing, two consecutive sinus impulses were conducted to the ventricles but this was not seen during the long recordings taken when in spontaneous idioventricular rhythm.This phase of conduction cannot be satisfactorily explained either by a vagal mechanism or refractory variations within the AV junctional tissue, and lends strong support to the recently challenged concept of a supernormal phase of conduction.
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D O Williams (1973) conducted a case report in Heart block (n=1). Endocardial pacing vs. Spontaneous idioventricular rhythm was evaluated on Supernormal phase of AV conduction of sinus impulses to the ventricles. Endocardial pacing in 1 patient with heart block delayed the supernormal AV conduction phase and enabled 2 consecutive conducted sinus impulses on 4 occasions vs 0 during spontaneous rhythm.
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