Rate-dependent changes in excitability of depressed cardiac Purkinje fibers as a mechanism of intermittent bundle branch block.
Population
Isolated bundles of Purkinje fibers placed in a three-chambered tissue bath
Design
Preclinical
Authors
Discussion
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Implication
Challenges necessity of phase 4 depolarization for intermittent bundle branch block; hypothesis-generating for excitability mechanisms, human validation required.
Structured PICO
P
Population
Isolated bundles of Purkinje fibers placed in a three-chambered tissue bath
I
Intervention
Induction of depressed excitability via sucrose solution superfusion (with controlled phase 4 slope) or Tyrode's solution with high concentrations of KCl and CaCl2 or isoproterenol (0.1 microgram/ml)
O
Outcome
Conduction impairment, block, and time dependence of conduction during premature stimulation or changes in basic cycle lengthsurrogate
Phase 4 depolarization and abnormally prolonged action potentials are not necessary for intermittent bundle branch block, which may instead be driven by time-dependent variations in excitability of depolarized conducting fibers.
Cite This Study
Jalife et al. (1983) studied this question.