Acute effects of pacing site on repolarization and haemodynamics of the canine ventricles

AIMS: To determine the repolarization duration gradients in different ventricular regions at atrial and ventricular pacing and to test the hypothesis that acute haemodynamic response to ventricular pacing is related to the lead position with respect to repolarization gradients. METHODS AND RESULTS: Repolarization durations estimated as activation-recovery intervals (ARIs) were measured from unipolar electrograms recorded in the subepicardial (Epi), mid-myocardial (Mid), and subendocardial (Endo) layers of the apical and basal parts of the right ventricle (RV) and left ventricle (LV) of 15 healthy dogs under atrial and ventricular pacing. Cardiac haemodynamic variables were measured as well. At atrial pacing, ARIs were shorter in Epi than in the innermost layers (P< 0.05) in the RV apex and LV base, but not in the LV apex and RV base. Activation-recovery intervals increased from apex to base and from base to apex in RV and LV, respectively (P ≤ 0.05). At apical or basal pacing of RV and LV, repolarization gradients decayed. The dispersion of repolarization increased at LV apical pacing and preserved at RV apical pacing. The pump function of a ventricle was altered dramatically at pacing of the area with the shorter ARIs and to a lesser degree at pacing of the area with the longer ARIs (P ≤ 0.051). CONCLUSION: The transmural and apicobasal differences in repolarization durations were heterogeneously distributed at atrial pacing. The acute haemodynamic response of the individual ventricle was better with pacing of the region with the longest repolarization suggesting a promising criterion for the lead position selection on the basis of ARIs measurements.