Electrophysiological profile after inward rectifier K channel blockade by barium in isolated rabbit hearts. Altered repolarization and unmasked decremental conduction property

AIMS: The aims of this study were to define the changes of cardiac conduction properties after selective IK1 blockade in isolated hearts. METHODS AND RESULTS: Intracardiac recording and stimulation in Langendorff-perfused rabbit hearts were used to define cardiac conduction properties after Ba2+, a well known IK1 blocker. Ba2+ prolonged the corrected QT interval and decreased, or even abolished, the amplitude of the T wave. The conduction time through the sinoatrial (SA interval), the atrioventricular node (AH interval) and His-Purkinje system (HV interval) were not significantly changed. However, at higher atrial pacing rates the HV interval was lengthened by Ba2+ in a frequency-dependent manner. The recovery curve of the His-Purkinje system (the relationship of H2V2 to V1H2) was changed by Ba2+ to a prematurity-dependent pattern (AV nodal behaviour). Such a response was neither observed with 4-aminopyridine (Ito blocker) nor with d-sotalol (IK blocker). The atrial and ventricular refractory periods as well as the relative refractoriness (measured by the difference between relative refractory period and the absolute refractory period) of the ventricular tissue were increased by Ba2+. CONCLUSION: The electrophysiological profile of selective IK1 block in isolated hearts revealed altered repolarization of cardiac tissue. The decremental conduction properties, which are normally present in the atrioventricular node (with a paucity of IK1), were unmasked by IK1 block in the His-Purkinje system. The T wave, particularly its amplitude, is more closely related to IK1 than to Ito.