The role of electrical uncoupling in the genesis of atrioventricular conduction disturbance

The contribution of electrical uncoupling between the atrioventricular (A-V) nodal cells to the genesis of A-V nodal conduction disturbance was studied in isolated rabbit hearts. The electrical coupling was estimated by measuring the input resistance through a microelectrode. The A-V nodal conduction time was measured by recording atrial and His bundle electrograms (A-H interval).Treatment with ouabain (6.8 × 10^?7 m) for an hour increased the input resistance of the A-V nodal cells with a concomitant prolongation of the A-H interval. It also decreased the action potential amplitude, the maximal rate of depolarization, and the resting potential of these cells.High calcium perfusate containing 3.6 mm, 5.4 mm and 7.2 mm Ca increased the input resistance of the A-V nodal cells dose-dependently associated with a prolongation of the A-H interval. No significant change in the action potential configurations of the A-V nodal cells was caused by the high calcium perfusate.The increase in the input resistance of the A-V nodal cells under these conditions was considered to reflect an increase in the axial resistance which would cause a reduction in the electrical coupling. It is suggested that the reduction in the electrical coupling between the A-V nodal cells plays an important role in the genesis of the A-V nodal conduction disturbance caused by ouabain or high calcium perfusate.