Research on Electrical Remodeling After Short Term Pacing in Canine Model

Objectives To evaluate the changes in atrial effective refractory period (AERP) proprieties and in ionic currents in PVs myocytes from dogs subjected to rapid atrial pacing in PVs and right atrial appendage (RAA) and to relate these changes to the ability to induce AF.Methods Twelve mongrel dogs in normal sinus rhythm were paced from the superior left PVs or RAA at 500 bpm for 4 hours. Electrophysiologic studies conducted to determine changes in AERP, dispersion and rhythm. Ionic currents were studies with the patch clamp technique in single PVs myocytes in sham operated dogs and compared with those from PVs pacing and RAA pacing groups.Results The presence of rapid atrial pacing was associated with a marked shortening in AERP in both PVs and RAA pacing group with a marked increase of AERP dispersion in PVs pacing. Both L-type calcium current (ICa, L) and the transient outward current (Ito) were reduced in both groups with an increased significance in PVs pacing group. The density of ICa-Lwas decreased significantly from (-6.03±0.63) pA/pF in the control group to (-3.21±0.34) pA/pF in PVs pacing group and (-4, 75±0.41) pA/pF in RAA pacing group (n=6, P<0.05) while the density of Ito was decreased significantly from (8.45±0.71) pA/pF in the control group to (5.21±0.763) pA/pF in PVs pacing group and (6, 84±0.69) pA/pF in RAA pacing group (n=6, P<0.05).Conclusions Our findings provide likely ionic mechanisms of shortened repolarization in induced atrial tachycardia with a decrease in ICa, L and Ito current densities which is the likely mechanism for a decrease in Action potential duration (APD) rate adaptation in the canine rapid pacing model more pronounced in PVs pacing group underlying the crucial role of PVs in initiating AF.