Viable Myocardium Impact on Left Ventricular Function after Late Revascularization of Infarct-related Artery in Acute Myocardial Infarction

Objectives The long-term benefit of late reperfusion of infarct-related artery （IRA） after acute myocardial infarction （AMI） is controversial, and the benefit mechanisms remain uncertain. Low dose dobutamine stress echocardiography （LDSE） can identify viable myocardium and predict improvement of wall motion after revascularization. Methods Sixtynine patients with first AMI who did not received early reperfusion therapy were studied by LDSE at 5 to 10 days after AMI. Wall motion abnormality and left ventricular size were measured at the same time. Successful PCI were done in all patients at 10 to 21 days after AMI onset. Patients were divided in two groups based on the presence or absence of viable myocardium. Echocardiography was repeated six months later. Results There were 157 motion abnormality segments. 89 segments （57%） were viable during LDSE. 26 patients （38%） with viability and 43 （62%） without. In viable group, left ventricular ejection fraction （LVEF） was increased （P 〈 0.05）, and left ventricular end systolic volume index （LVESVI） and wall motion score （WMS） were decreased （P 〈 0.05 and P 〈 0.01） significantly at 6 months compared with baseline. But in patients without viability, LVEF was decreased （P 〈 0.01）, and LVESVI and left ventricular end diastolic volume index （LVEDVI） were increased （P 〈 0.05） significantly after 6 months, and the WMS did not changed （P 〉 0.05 ）. LVEF increased （P 〈 0.05 ） and WMS decreased （P 〈 0.05） on LDSE during acute phase in patients with viability, but they were not changed in the nonviable group. Conclusions Late revascularization of IRA in patients with presence of viable myocardium after AMI is associated with long-term preservation left ventricular function and less ventricular remodeling. Improvement of left ventricular systolic function on LDSE indicates late phase recovery of left ventricular function after late revascularization.

Detection of viable myocardium by low dose of dobutamine cine MR imaging in miniswine

Objective To evaluate the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for myocardial viability.Methods Ten male miniswines underwent left ventriculography and coronary angiography, followed by stenosis of the left circumflex coronary artery (LCX) using ameroid constrictor. More than one month later, left ventriculography and coronary angiography were performed again, followed by cine-MRI at rest and during stress with incremental dose of dobutamine 5 -20 μg·kg-1·min-1. Traditional and/or breath-hold cine-MRI were used to evaluate regional left ventricular wall motion, corresponding to basal, midventricular and apical short-axis tomograms. Regional wall motion score index (WMSI) was calculated. The miniswines were finally sacrificed for pathological examination. Triphenyl tetrazolium chloride ( TTC) delineated myocardial infarction. Microscopy was used to identify myocardial cellular changes.Results One pig died, one pig suffered from aneurysm and another showed no negative findings. The other seven pigs were found with hypokinetic (n = 4) or akinetic (n = 3) myocardial regions related to stenosed LCX. Their mean WMSI at rest for the lateral and posteroinferior walls (ischemic regions) of the left ventricle was 2. 27±0.32, as compared with 1. 00±0. 00 ( P < 0. 01) for the corresponding nonischemic anteroseptal regions. Further, the mean WMSI for the ischemic regions was 2. 27±0. 32 at rest compared with 1. 40±0. 39(P<0. 01) at the dose of dobutamine 5 μg·kg-1 ·min-1. However, the mean WMSI at the doses of dobutamine 10 and 20 μg·kg-1·min-1 were 1. 70±0. 76 and 1. 75±0. 83, respectively, with no significant difference as compared with the mean WSCI at rest (P>0. 05). The pathologic examination showed viable myocardium at the ischemic regions.Conclusion Low-dose dobutamine (5μg·kg-1·min-1) recovers hypokinetic or akinetic myocardial regions, and dobutamine stress MRI can be used to detect myocardial viability.

Effects of Late Reperfusion on Left Ventricular Function and Its Relationship With Viable Myocardium After Acute Myocardial Infarction in Patients With or Without Diabetes

Objectives To compare the different effects of late successful reperfusion with PCI on left ventricular function and its relationship with viable myocardium after acute anterior wall myocardial infarction in patients with or without diabetes. Methods A total of 125 consecutive subjects with acute anterior wall myocardial infarction were selected, and divided into diabetes mellitus （DM） group （ n = 43） and Non-DM group （ n = 82） according to WHO diabetes diagnosis criteria. All patients received successful PCI at 12 ± 8 days from onset. Ischemic viable myocardium was detected with low-dose dobutamine echocardiography, and left ventricular function and wall motion abnormality were also assessed with echocardiography before PCI. The data of clinical manifestations and angiograms before and after PCI were analyzed. Levels of creatinine kinase-MB （CK-MB）, and troponin T （TnT） before PCI, 6 hours and 24 hours after PCI were assessed. All patients received clinic and echocardiography follow-up for 6 months. Results Higher rate of TIMI 2 flow, and lower rate of TIMI 3 flow in DM group were demonstrated immediately after PCI, and the rate of serum CK-MB and/or TnT levels were higher in DM group, compared with Non-DM group（P 〈 0.05）. 63% of DM patients and 56% of non-DM patients had viable myocardium before PCI（ P 〉 0. 05）. There were no significant differences of left ventricular ejection fraction （LVEF）, left ventricular end diastolic volume index （LVEDVI）, left ventricular end systolic volume index （LVESVI）, and wall motion score （WMS） between two groups at baseline before PCI（P 〉 0.05）. After six months, WMS was decreased and LVEF was increased in Non-DM group, but the WMS and the LVEF did not changed, and the LVEDVI was increased in DM group compared with baseline; the LVEDVI, LVESVI, LVEF, and WMS were significantly different between two groups （P 〈 0.05 or P 〈 0. 01 ）. Conclusions Compared with non-diabetics, delayed successful revascularization with PCI in diabetics patient with acute myocardial infarction has less benefitial effect on the improvement of late phase left ventricular function, and it may be because the insufficient reperfusion or reperfusion injury to myocardium but not the viable myocardium contributing to the poor result. （S Chin J Cardiol 2009; 10（4） ： 196 -203）

Early prediction of myocardial viability after acute myocardial infarction by two-dimensional speckle tracking imaging

Background Identifying the transmural extent of myocardial necrosis and the degree of myocardial viability in acute myocardial infarction （AMI） is important clinically. The aim of this study was to assess myocardial viability using two-dimensional speckle tracking imaging （2D-STI） in patients with AMI. Methods 2D-STI was performed at initial presentation, three days, and six months after primary percutaneous coronary intervention （PCI） in 30 patients with AMI, who had a left anterior descending coronary artery （LAD） culprit lesion. In addition, 20 patients who had minimal stenotic lesions （〈 30% stenosis） on coronary angiography were also included in the control group. At six months dobutamine echocardiography was performed for viability assessment in seven segments of the LAD territory. According to the recovery of wall motion abnormality, segments were classified as viable or non-viable. Results A total of 131 segments were viable, and 44 were nonviable. Multivariate analysis revealed significant differences between the viable and nonviable segments in the peak systolic strain, the peak systolic strain rate at initial presentation, and peak systolic strain rate three days after primary PCI. Among these, the initial peak systolic strain rate had the highest predictive value for myocardial viability （hazard ratio： 31.22, P 〈 0.01）. Conclusions 2D-STI is feasible for assessing myocardial viability, and the peak systolic strain rate might be the most reliable predictor of myocardial viability in patients with AMI.