| Myocardial bridge (MB) is a congenital anatomic variation. Normally, the main coronary arteries and the proximal segments of their major branches lie free on the surface of the heart under the epicardium. In some instances, these vessels goes intramurally through the myocardium, resulting in the tunneled segment compressed and make the lumen narrow as a stenosis or occlusion during the systolic phase. The myocardium that covers the artery is defined as a myocardial bridge and the artery itself is defined as a mural coronary artery (MCA) or tunneled segment. In the proximal of the mural coronary arteries, the prevalences of the atherosclerotic plaques reaches as high as 86%, significantly higher than the MCA and the distal segment. In the past, MB was considered to be a benign variation, but many recent reports have implied that MB can impact the coronary flow and lead to hemodynamic abnormalities, causing a series of clinical symptoms such as angina, myocardial infarction, life-threatening arrhythmias and even sudden death. Much research has been done on the hemodynamic state in the patients with MB, but the study on the systolic function is very limited so far. The current evaluation of systolic function of left ventricle in two-dimensional echocardiography, such as stroke volume, ejection fraction ,wall-motion analysis and other indicators, are usually normal, then are the contraction of heart totally unaffected?Speckle tracking imaging (STI) has emerged as an alternative technique that analyzes motion by tracking natural acoustic reflections and interference patterns within an ultrasonic window. The imaging-processing algorithm tracks user-defined regions of interest which are comprised of blocks of approximately 20 to 40 pixels contain stable patterns that are described as speckle. Using analytical software to calculate strain, strain rate, rotation angles and other indicators to assess the movement of myocardium, then get a knowledge of the global and regional function of the heart. In this study, STI were used for quantitative assessment the influence on regional and global left ventricular systolic function by myocardial bridge of the left anterior descending (LAD) coronary artery.Part 1. The assessment of left ventricular systolic function in patients with myocardial bridge of the left anterior descending coronary arteryIn this part, to probe into the speckle tracking imaging assessment of the influence on regional left ventricular systolic function by myocardial bridge of the left anterior descending coronary artery. 21 symptomatic patients with myocardial bridge of LAD, 19 patients with myocardial bridge of LAD accompany with stenosis of proximal mural coronary artery verified by coronary angiogram and 30 patients of the control group were entrolled in this study. Compare the peak longitudinal systolic strain (LS) of the endo-myocardium and epi-myocardium of the left ventricle 18 segments. RESULTS①The LS of the endo-myocardium were higher than that of the epi-myocardium in all 18 segments in the control group (P<0.05).②In the MB group, there were no differences of the LS between the endo-myocardium and epi- myocardium in the anterior and anteroseptal at the level of papillary muscle and apex (P>0.05); The LS of the endo-myocardium and epi-myocardium in all segments were not statistically different from the control group (P>0.05).③In the MB of LAD accompany with stenosis of proximal MCA groups, the LS are lower than that of the control group and the groups with MB of LAD in most segments supplied by the left anterior descending coronary artery (P<0.05). Part 2. Evaluation of left ventricular twist in patients with myocardial bridge of left anterior descending coronary arteryThe aim of this part is to assess the differences in subendocardial and subepicardial left ventricular twist in patients with myocardial bridge of the left anterior descending coronary artery by using STI. 21 symptomatic patients with myocardial bridge of LAD, 19 patients with myocardial bridge of LAD accompany with stenosis of proximal mural coronary artery verified by coronary angiogram and 30 patients of the control group were entrolled in this study. The two-dimensional loop-cinec were obtained at the left ventricular short-axis view of such groups above. Compare the peak subendocardial and subepicardial global rotation of the level of basal and apical planes. RESULTS①As seen from the apex, left ventricle performed a wringing motion with a clockwise rotation at the base and countclockwise rotation at the apex in all groups.②The peak global rotation of the subendocardium was obviously greater than the one of the subepicardium in the basal and apical planes in all subjects (P<0.05); the peak subepicardium left ventricular twist was also lower than the peak subendocardium.③There were no differences of the peak global rotation of the subendocardium and the subepicardium between the control group and the MB group of LAD (P>0.05).④In the MB of LAD accompany with stenosis of proximal mural coronary artery groups, the peak global rotation of the subendocardium and the subepicardium in the apical plane are significantly lower than that of the control group and the groups with MB of LAD (P<0.05), the peak subepicardium and subendocardium left ventricular twist were also impaired, but have no difference in the basal plane.CONCLUSIONS①Speckle tracking imaging can exactly evaluate the local and global contractile function in patients with myocardial bridge of the left anterior descending coronary artery.②Isolated myocardial bridge would lead to the abnormalities of regional myocardial contractile function, but the global rotation keep normal.③Accompany with stenosis of proximal mural coronary artery, the LS of myocardial segments supplied by MCA were lower; In the apical plane, the global rotation of subendocardium and subepicardium of such segments were significantly impaired. The segments involved maybe have transmural ischemic injury. ④In the symptomatic patients with MB of LAD, the regional left ventricular systolic functions are impaired, the atheromatous plaque probably work for this. |
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