Abstract 255: Mechanical Stretch is Not a Major Cause of Ectopic Activation During Early Stage Regional Ischemia in an Isolated Left-Ventricular Working Heart Model

Abstract

Background: Acute regional ischemia is a leading cause of death. Ectopic beats may initiate ventricular arrhythmias in the first hour after coronary occlusion; however, the origin of these beats remains poorly understood. Some studies suggest that abnormal mechanical stretch at the ischemic border zone may contribute to the initiation of ectopy. If mechanical stretch plays a major role in triggering ectopic beats, we therefore expect: I , left ventricular working (LVW) hearts will have higher frequency of post-occlusion ectopic activity than non-beating (NB) hearts; II , in LVW hearts, ectopic beats will arise from ventricular sites undergoing mechanical stretch. Methods and Results: Isolated pig hearts were assigned to NB or LVW groups (8 per group) and prepared for Langendorff or LVW perfusion, respectively. Contraction of NB hearts was suppressed with 10 μM blebbistatin. Acute regional ischemia was induced by LAD occlusion. Using a newly developed optical mapping system, electrical activity and mechanical deformation were simultaneously recorded from 0 to 60 minutes after LAD occlusion. Mechanical stretch (positive strain in 2 principal directions) was observed in the ischemic and border zones of LVW but not NB hearts (Figure, Panel A). There was no significant difference in the number of ectopic events in LVW hearts compared to NB hearts (58±35 vs. 32±36, p=0.17). Of the 45 ectopic events that originated from the LV mapping region in LVW hearts, <20% (6) were from sites that underwent mechanical stretch in the prior cardiac cycle (Figure, Panel B). Conclusion: Mechanical stretch does not play a major role in triggering ectopic beats in early acute regional ischemia in this model.