Isopotential and isochronal epicardial mapping during external cardiac pacing in dogs

To investigate cardiac entrainment by external pacing, ventricular epicardial mapping was performed in dogs with atrio-ventricular block. Isopotential maps recorded with 128 unipolar leads during the stimulation artifacts showed that the electrical field was little affected by the electrode type and depended mostly on the electrode position. An antero-posterior electrode pair produced a reproducible and uniform apex-to-base potential gradient which induced activation sequences showing inter-individual differences: the areas of initial activation tended to remain the same in each dog (e.g., apical, apico-lateral, antero-septal) despite changes in the stimulation protocol. Inverting the polarity of the current did not change the site of origin of activation (81% remained the same). Increasing the current intensity from 99 to 120 mA, decreased the total epicardial activation time from 86±16 to 61±16 ms (p<0.05). In conclusion, this preliminary study indicates that epicardial mapping may provide useful information about the cardiac response to external pacing