To Explore The Morphology Of The Myocardial Bridge And Its Correlation Factor Analysis

Objective:The aim of the present study was to provide the correlation between the structural characteristics,classification in Myocardial bridge(MB)–mural coronary artery(MC) and the changes of the tunica intima of the coronary artery through the observation and analysis of anatomical and histological structure of MB and mural coronary artery and the coronary artery of the normal heart specimens, so that provide theoretical basis for the correlation between the function of MB and the occurrence of coronary heart disease.Material: The present research was carried out on 96 cases of the human hearts, 63 cases of the male, 33 cases of the female. The hearts were preserved in 4% formalin PBS solution.Methods:1.Grouping:In 96 cases of the human hearts, divided into 3 groups by age: 0～20 years older,20～40 years older, above 40 years older. First, to find out the beginning of the coronary artery, the perivascular fatty tissues was carefully removed, along the epicardial course of the coronary arteries and its branches, to find out the MB, then they were divided into two groups: one group with MB in the left anterior descending (experimental group) and anther group without MB (control group ).2.Anatomical observations:To MB groups, record the occurrence of myocardial bridge,location,type,the direction of fiber of the MB. The width of the MB is the maximum distance, which the fibers run across mural coronary artery. The length is the distance from initial point to the end point of MB. The thickness is the distance from the surface of the MB to the surfaces of the mural coronary artery. The datas were measured by Vernier caliper, the protractor and the ruler. The accuracy is 0.02mm.3.Histological observation:Experimental groups: the mural coronary artery in the left anterior descending was removed from the hearts together with surrounding adipose and myocardial bridge. Cut out mural coronary artery and cut out a 2cm-long proximal to mural coronary artery and a 2cm-long distal to mural coronary artery.Contral groups: These hearts without MB sections with the length of 2 cm were obtained from the beginning of the anterior interventricular branch, take 3 consecutive 2cm-long sections and named as proximal section,middle section,distal section according to the distance.The samples embedded in paraffin,sliced(Cross cut,Longitudinal cut),stained with HE. They were observed under the Nikang AZ100 Stereoscope microscope and gathered the pictures with the computerized image analyzer. SigmaScan Pro 5 measured and analysised the blood vessel caliber, internal membrane thickness.4.Results:1. Result of anatomy observation:(1) In 96 cases (male 63 cases, female 33 cases) of human hearts, 59 cases (61.45%) presented myocardial bridge. Among of them, the male and female occupy 40 cases (63.49 %) and 19 cases (57.58%) respectively.(2) All of the MB, 44 cases were located in the left anterior descending, 5 cases in the diagonal branch, and 7 cases in the left circumflex arteries, 7 cases in the anterior branch of right coronary artery, 3 cases in the posterior interventricular branch of right coronary artery. Among of the 59 cases of MB, Single bridge was found in 53 cases and multiple bridges were observed in 6 cases (five with double bridges and one with triple bridges).(3) Average distance from MB to the coronary sinus is (5.68±3.98)cm.(4) The length,width,thickness of the MB were (19.45±11.02)mm,(3.35±1.39)mm,(2.20±1.22)mm respectively.(5) The average angle between the direction of the musculature and of the vessels is 45.01±25.39°.2. Result of histology observation:(1) The thickness of the tunica intima of the coronary artery increased thickness with ageing, especially from the adult to the senior citizens. The tunica intima is relatively stable, after 40 years old. The tunica intima thickness of the two adjacent segments had no statistical significance (P>0.05) in the same age group.(2) The average tunica intima thickness of proximal to the mural coronary artery was 383.48±186.18μm. The segment of MC was 119.89±54.18μm. The distal segments was 195.77±99.21μm. The tunica intima of the anterior segment of the mural coronary artery was significantly thicker than that of the posterior and inferior segment (P<0.05). The tunica intima of the segment of the mural coronary artery was significantly thinnner than that of the posterior segment (P<0.05).(3) There were positive correlation between the length,thickness of the MB and the intima of the proximal segment to the mural coronary artery. There were negative correlation between the length,thickness of the MB and the intima of the segment of the mural coronary artery, after 20 years old.Conclusion:(1) In autopsy, occurrence of myocardial bridge was 61.45%;The most common location of myocardial bridges was over the outset 1/3 section of the interventricular branch of the left coronary artery;It mainly appears by the sole form; Average distance from MB to the left coronary sinus is 4.86±1.74 cm;The average angle between the direction of the musculature and of the vessels is 45.01±25.39°;(2) The normal coronary artery intima thickness increases with the aging. The intimal thickness is proportional to vascular caliber and blood-fluid pressures. Myocardial bridge is obviously much greater than the impact of aging changing for the intimal of the normal coronary.(3) The myocardial bridges can promote thickening intima of the proximal to the mural coronary artery. The myocardial bridge can reduce the thickness of MC intima.The myocardial bridge has the function to promote atherosclerosis to the intima of the pro-MB, Myocardial bridges may provide protection against the formation of atherosclerotic plaque to the mural coronary.