Abstract
372
Background: Left ventricular mechanical dyssynchrony (LVMD) may occur after acute myocardial infarction (AMI), and is closely associated with left ventricular (LV) dysfunction and poor prognosis. Previous studies found that LVMD is present in the infarcted area after AMI. However, whether the mechanical dyssynchrony present in remote myocardium outside the infarct area remains controversial. The mechanism of global and regional LVMD after AMI and its pathophysiological changes have not been well established.
Objectives: To quantitatively evaluate the global and regional LVMD early after AMI by phase analysis of single photo emission computed tomography gated myocardial perfusion imaging (SPECT GMPI) and further to explore the underlying mechanism.
Methods: Bama minipigs (n = 11) were subjected to left anterior descending (LAD) occlusion by balloon to introduce AMI models. All animals underwent SPECT GMPI before, 1 day and 1, 4 weeks after LAD block, respectively. Global bandwidth(BW), regional BW, regional summed motion score(SMS) and regional summed thickening score (STS) were measured by SPECT GMPI. Meanwhile, myocardial injury markers and 12-lead electrocardiogram were detected at the corresponding time points. After the last SPECT GMPI, the hearts of AMI models were excised for histopathological analysis. Repeated measurement ANOVA, paired t tests, and pearson linear correlation analysis were performed to analyze the data.
Results: 8 pigs were successfully established as AMI models and complete the study. The BW in the infarct area (LAD-dominated area) at 1 day, 1 week and 4 weeks post-AMI was significantly higher than that pre-AMI, so was the BW in the non-infarct areas (LCX, RCA-dominated area), which revealed less dyssynchrony at 3 time-points post-AMI when compared with the infarct area. The global LVMD is positively correlated with the mechanical dyssynchrony in the infarct area (r= 0.762~0.884, all P < 0.05). Furthermore, the changing trend of global LVMD is in concert with regional mechanical dyssynchrony in the infarct area. The regional mechanical dyssynchrony parameter BW in the non-infarct area after AMI showed moderate to good correlation with regional SMS (r = 0.734~0.841, all P < 0.05) and regional STS (r = 0.724~0.836, all P < 0.05), respectively. HE staining showed myocardial edema, hypertrophy and steatosis, accompanied by inflammatory cell infiltration in the remote myocardium.
Conclusions: The mechanical dyssynchrony occurs in both the infarct and non-infarct areas. The global LVMD is mainly influenced by the mechanical dyssynchrony in the infract area. The extent of mechanical dyssynchrony in non-infarcted myocardium is closely associated with the abnormality of regional wall thickening and motion, which represents the decreased myocardial contractility. The reduced wall thickening and motion in normal perfusion myocardial segments may be an effective therapeutic target to improve the mechanical dyssynchrony of non-infarcted myocardium.