Increased wave break during ventricular fibrillation in the epicardial border zone of hearts with healed myocardial infarction

Background-The action potential duration (APD) restitution hypothesis of wa ve break during Ventricular fibrillation (VF) in the epicardial border zone (EBZ) of hearts with chronic myocardial infarction is unknown. Methods and Results-VF was induced by rapid pacing, and the EBZ with the tw o adjoining sites (right ventricle and lateral left ventricle) were sequent ially mapped in random order in 7 open-chest anesthetized dogs 6 to 8 weeks after left anterior descending artery occlusion and in 4 control dogs. At each site, 3 seconds of VF was mapped with 477 bipolar electrodes 1.6 mm ap art. The number of wave fronts and approximate entropy were significantly ( P<0.01) higher in the EBZ than all other sites in both groups independent o f the rate of invasion of new wave fronts and epicardial breakthroughs, The higher wavelet density in the EBZ was caused by increased (P<0.01) inciden ce of spontaneous wave breaks. There was no difference between the two grou ps in either reentry period (80 episodes) or VF cycle length. Reentry in th e EBZ had a smaller core perimeter, slower rotational speed, and a small or no excitable gap (P<0.01), often causing termination after one rotation. T he dynamic monophasic action potential duration restitution curve in the EB Z had longer (P<0.01) diastolic intervals, over which the slope was >1. Con nexin43-positive staining was significantly (P<0.01) and selectively reduce d in the EBZ. Conclusions-A selective increase in wave break and alteration of reentry oc cur in the EBZ during VF in hearts with healed myocardial infarction. Incre ased wave break in the EBZ is compatible with the action potential duration restitution hypothesis.