Abstract 14603: Post-Myocardial Infarction Secondary Mitral Regurgitation Elevates Circumferential Strain in the Remote Zone and Contractile Dyssynchronicity in a Swine Model

Abstract

Introduction: Post-myocardial infarction (MI) secondary mitral regurgitation (SMR) worsens left ventricular function and mortality, due to the volume overload it imposes on the ventricle. In this study, we sought to investigate the effects of the volume load from SMR on regional myocardial mechanics and dyssynchrony. Methods: Ten Yorkshire swine were induced with MI by occluding the left circumflex branch. Cardiac MRI and PV loop were performed at baseline (prior to MI), and at termination (3 months after MI). SMR was quantified using epicardial echo. Pigs were divided into 2 groups: no/mild MR (nmMR, n=4) and moderate/severe MR (msMR, n=6). MRI images were analyzed to measure infarction size, end-diastolic (EDV) and end-systolic volume (ESV), circumferential strain (CS), and standard deviation of time to peak of CS as systolic dyssynchrony index (SDI) to evaluate the dyssynchrony. The myocardial region was divided into the infarction, border, and remote zone, based on the LCx-supplied region (Fig. A and B1) . Results: There were no differences in infarction size between the two groups. The changes (Δ) of EDV and ESV from baseline to 3M were greater in msMR compared to nmMR (63.8±24.6mL vs 33.5±9.2 mL, p<0.05, and 48.1±18.9 mL vs 23.0±4.9 mL, p<0.05, respectively) (Fig. B) . Group-wise comparison of CS between baseline and 3M for each zone demonstrated that CS in the infarction zone decreased in both groups. However, CS in the remote zone was elevated at 3M only in msMR (-12.07±3.65 % vs -16.36±3.07 %, p<0.01) and there was a strong correlation between EDV and CS in the remote zone (Pearson r=-0.6614, p=0.01) (Fig. C) . Also, SDI of CS was significantly elevated at 3M in msMR (0.09741 vs 0.1255, p=0.015) (Fig. D) . Conclusions: Elevated CS in the remote zone and dyssynchrony due to volume load could impair LV function, potentially increasing oxygen demand and reducing pumping efficiency.