Effect of the left ventricular overload on epicardial repolarization in the rabbit.

Objective: We have investigated the local durations and sequence of repolarization in the ventricular epicardium in the rabbit under the increase of the left ventricular (LV) afterload.

Methods: The LV overload was produced by the 1-minute aortic stenosis up to systolic blood pressure of 140 mm Hg. The experiments were carried out on eight anaesthetized rabbits (urethane, 1.5 g/kg, ip). Unipolar electrograms were simultaneously recorded from 64 ventricular epicardial leads at 33 degrees C.

Results: At baseline state, the shortest activation-recovery intervals (ARIs) were observed in the right ventricular (RV) base, the longest ARIs in the LV apex and lateral wall, and ARIs of intermediate durations in the RV apex and LV base. According to ARI distribution, a significant gradient in repolarization times was observed between the apex and base (p<0.01). Under acute LV overload, the repolarization duration increased significantly (p<0.01) locally at the LV apex and adjacent area of the free wall. Dispersion of repolarization is increased in the apex. A decrease of ARIs (p<0.05) was observed at the RV base, as well.

Conclusion: Under acute increase in the LV afterload, ventricular epicardial activation sequence remained largely unaltered which, along with changes in local repolarization durations, resulted in the repolarization sequence being quite similar to the baseline one. The earliest repolarization occurred in posterobasal region of RV whereas the areas over the LV apex and adjacent area of the free wall were the last to repolarize.