Abstract 9825: Cardiac Strain in a Swine Model of Regional Hibernating Myocardium: Effects of Bypass Surgery on Contractile Reserve

Abstract

Background: Clinical studies have suggested that functional recovery of hibernating myocardium may be delayed following coronary artery bypass graft (CABG) surgery. We have shown in a swine model of hibernating myocardium, that recovery of regional function and oxygen consumption during an infusion of high dose catecholamine is sub-maximal at 4-weeks following CABG. Using the same swine model of hibernating hearts along with MRI estimates of circumferential strain (ECC), we tested whether contractile reserve within hibernating myocardial regions during a low dose infusion of dobutamine improves post-CABG. Methods. Ten pigs underwent thoracotomy with placement of a constrictor around the LAD artery. At 12 weeks, MRI imaging was performed prior to CABG and repeated 4-weeks following off-pump revascularization with a left internal mammary artery graft to the LAD artery. MRI studies were performed at baseline and during an infusion of low dose dobutamine (5 μg/kg/min). Results: MRI studies prior to CABG showed that circumferential strain in the Hibernating (LAD) Region was lower than the Remote Region at rest (-14.5±0.7 versus -15.1±0.7 respectively; P<0.05) and did not improve during dobutamine (-14.7±0.8 versus -16.7±0.8 respectively; P<0.05). Following CABG, strain measurements in the hibernating LAD region remained lower than remote regions at rest, but improved during the same dose of dobutamine (Figure). Summary: Baseline function in hibernating myocardium does not fully recover at 4 weeks post-CABG but contractile reserve during an infusion of low dose dobutamine does improve compared with estimates of strain obtained prior to surgery. Future studies should address the time course of recovery of regional function post-CABG and test whether additional interventions might facilitate earlier recovery of contractile reserve.