WALL THICKNESS OF MAJOR CORONARY ARTERIES IN PAKISTANI POPULATION.
Objectives: To measure the wall thickness of major coronary arteries in Pakistani population, through micrometry.
Study design: An observational study.
Place and duration of study: Combined Military Hospital Rawalpindi, Khyber Medical College Peshawar and District Headquarter Hospital, Rawalpindi, in collaboration with Departments of Anatomy and Pathology, Army Medical College Rawalpindi. The duration of study was six months with effect from September 2009 to March 2010.
Material and methods: After incising pericardium, 1mm long segments of major coronary arteries i.e. right coronary artery (RCA), left anterior descending artery (LAD) and left circumflex artery (LCX) were taken 1cm distal to their origin, from adult male cadavers of up to 40 years age. After processing for paraffin embedding, 5um thick sections were prepared, mounted on glass slides and subsequently stained with Hematoxylin and Eosin (H and E) for routine histological study. Verhoeff's elastic stain was used to make the elastic lamina more prominent. Wall thickness for each section was measured through micrometry, circumferentially at eight different places along the planes at 45o to each other and then their mean taken as a reading for the respective artery.
Results: The total wall thickness of major coronary arteries and of the individual tunicae was less in Pakistani population. The mean thickness of RCA was 0.61+-0.05 mm; LAD had mean thickness of 0.55 +-0.06 mm whereas that of LCX was 0.66 +-0.13 mm. The mean thickness of tunica intima of RCA was noted to be 0.230 +-0.044 mm; tunica media measured 0.205 +-0.031 mm whereas tunica adventitia was 0.172 +-0.023 mm thick. The mean thickness of tunica intima of LAD measured 0.156 +-0.032 mm; tunica media was observed to be 0.224 +-0.026 mm thick whereas the tunica adventitia was 0.170 +-0.032 mm thick. The mean thickness of tunica intima of LCX was observed to be 0.203 +-0.059 mm; tunica media to be 0.282 +-0.097 mm whereas that of tunica adventitia was noted to be 0.179+-0.037 mm.
Conclusion: The normal mean values of total wall thickness and of each of the individual tunica of coronary arterial wall in Pakistani population are lower than those reported in international literature. This might be due to geographic and / or ethnic variations in the histological structure of coronary arterial wall.
The available literature shows a great variety of histomorphometric observations of coronary arteries in different populations of the world1-3. There is paucity of data on the histological features of the major coronary arteries in Pakistani population and, to our knowledge, no reference cadaveric data is available on the histological features of human coronary arteries. The present study was designed to conduct the histomorphometric analysis of coronary arteries in Pakistani population. Since the reported observations are based largely on a study of relatively few normal hearts and because of the difficulty in obtaining material that would give a fair representation of what might be called the normal coronary vessel, this study was made on twenty carefully chosen specimens. Diseases that were likely to implicate the coronary vessels were excluded, as were those hearts that showed obviously diseased coronary arteries on gross inspection.
The results of this study will serve as a baseline reference data in medico-legal investigations of undiagnosed and / or sudden deaths in this part of the world.
MATERIAL AND METHODS
The study was conducted on twenty adult male hearts obtained during routine autopsies at CMH Rawalpindi, Khyber Medical College Peshawar and DHQ Hospital, Rawalpindi from Sept 2009 to March 2010, in collaboration with Depts of Anatomy and Pathology, Army Medical College Rawalpindi. The cause of death was accident, suicide or homicide and therefore occurred suddenly. History was taken from the relatives of the deceased in order to exclude cases with risk factors for coronary artery disease (CAD). The time lapsed between death and autopsy was 12-72 hours. The protocol for the research project was approved by a suitably constituted Ethics Committee of the institute and the study conformed to the provisions of the Declaration of Helsinki in 1995 (as revised in Edinburgh, 2000). Weight was recorded, and hearts weighing more than 400 grams were excluded to avoid the possibility of hypertensive cases.
Hearts showing obvious pathological changes of atherosclerosis were also excluded. After incising pericardium, 1mm long segment of major coronary arteries i.e. right coronary artery (RCA), left anterior descending artery (LAD) and left circumflex artery (LCX) were taken 1cm distal to their origin, from adult male cadavers of up to 40 years age4. Segments of the coronary arteries were fixed in 10% formalin and processed for paraffin embedding.
Sections of paraffin blocks were prepared at 5um thickness, mounted on glass slides and subsequently stained with Hematoxylin and Eosin (H and E) for routine histological study. Verhoeff's elastic stain was used to make the elastic lamina more prominent in order to clearly differentiate the various tunicae. Wall thickness for each section was measured through micrometry, circumferentially at eight points along the planes at 45o to each other and then their mean taken as a reading for the respective artery5.
In all the slides, thickness of tunica intima was measured from luminal border upto internal elastic lamina; tunica media was measured between internal elastic lamina and external elastic lamina whereas thickness of tunica adventitia was measured from external elastic lamina up to its outermost boundary which could be easily identified. Mean thickness of each of the tunica intima, tunica media and tunica adventitia and of total wall were calculated separately for the elementary coronary arteries i.e. RCA, LAD and LCX. Slides were observed with an Olympus BX41 multi-head microscope and digitally photographed. Data was analyzed using SPSS (Statistical Package for Social Sciences) windows version 18. Descriptive statistics were used to describe the data. Mean and Standard deviation (SD) were calculated for quantitative variables. Analysis of variance (ANOVA) was used to compare quantitative variables between main coronary arteries.
The age of study population ranged from 21 to 36 years with a mean +- SD 29.0+- 4.16 years. Heart weights of all the specimens was determined before studying which ranged from 243 to 397 grams with a mean value of 314.15+-36.60 grams.
The mean total wall thicknesses and of each of the individual tunica of major coronary arteries (RCA, LAD, LCX) were measured through micrometry in this study (Table 1 and 2).
Table-1: Mean values of total wall thickness of main coronary arteries (in mm)
Math coronary arteries###n###MIN###MIN###MAX###S.D
Table-2: Mean tunicae thickness of rca, LAD and LCX.
values are given in mm
The tunica adventitia was observed to consist of a meshwork of connective tissue. Particularly in the inner layers of the adventitia were found elastic fibers running largely in a circular direction. The media consisted of smooth muscle, circular in arrangement with scattered circularly arranged elastic elements among the smooth muscle fibers that were generally more conspicuous towards the outer layers of the media. The intima, as a function of age, consisted of splitting of the internal elastic lamina into two membranes between which smooth muscle fibers were seen, constituting the 'musculoelastic layer'. The outermost of these elastic membranes represented the border line between intima and media - the internal elastic lamina whereas the innermost layer labeled as "inner limiting membrane".
The earlier data on dimensions of coronary arteries is based on angiographies / echocardiographies of living subjects mostly with symptomatic CAD1-3.
The coronary arterial wall comprises three concentric layers: an inner (luminal) layer, the tunica intima; a middle layer, the tunica media; and an outer layer, the tunica adventitia6. In our study, the mean total thickness and mean thicknesses of individual tunicae of major coronary arteries (RCA, LAD, LCX) were measured through micrometry, as described by Joshi et al.5. The mean total thickness of each individual major coronary artery is less than those reported in literature and collected from living subjects1-3. The mean thickness of each individual tunica of RCA, LAD and LCX was also less than those reported in literature and collected from angiographic studies3. The reason for lower values of wall thickness in our study is the postmortem changes since postmortem changes and decomposition are always present at autopsy7.
The circumferential shrinkage of all the layers of vessel wall with fixation and then subsequent processing (embedding and dehydration) is an established fact8 and results in a decrease in wall thickness. The observations of Siegel et al9. support the results of wall thickness in our study, being less than those reported in angiographic and echocardiographic studies which are conducted in living subjects with symptoms of CAD and having significant intimal atherosclerotic thickening of coronary wall, though atherosclerosis is somewhat a normal aging phenomenon and has been reported to begin right from the infancy10. Additionally, great care had been taken in implementing the selection criteria. The subject population selected was below 40 years of age with no apparent risk factors for CAD, resultantly giving a picture of somewhat normal coronary arterial dimensions in our population. Our study supports the observations of Podesser et al11.
who, in an autopsy study on 52 coronary arterial segments of 10 Austrian adults, observed the wall thickness of coronary arteries ranging from 0.08 - 0.80 mm. Furthermore, even in normal patients and with no history of CAD, the wall thickness of coronary arteries has been reported to be greater than ours1,2 and hence contradicting our observations. This must be indicating the factor of geographic and/or ethnic variation too, as a reason for lower observed values in our study.
In our study, LAD at its origin presented a histological picture of that of an elastic artery, with tunica media being the thickest of all the three layers; tunica intima is relatively thick and tunica adventitia is relatively thin (Fig. 1).
RCA has a histological picture of that of a medium sized muscular artery, having almost same size tunica media and adventitia6. LCX at its origin has characteristics intermediate between elastic and muscular arteries; as a clue to its elastic nature, it has thickest tunica media and relatively thick tunica intima and behaves as a muscular artery due to having a relatively thicker tunica adventitia.
The results of this study serve as a reference normal data set against which to compare lumen dimensions in various pathological states. It should be of particular value in the investigation of diffuse atherosclerotic disease in cases of sudden or undiagnosed deaths.
The normal mean values of total wall thickness and of each of the individual tunica of coronary arterial wall in Pakistani population are lower than those reported in international literature.
Future studies should look for the changes in histological structure of coronary arteries with age and sex by employing immunohistochemical techniques. Genetic studies assessing both genotype and phenotype would be required to assess the role of genetic factors in micro-anatomic variations.
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2. Fayad ZA, Fuster V, Fallon JT, Jayasundera T, Worthley SG, Helft G, Aguinaldo JG, Badimon JJ, Sharma SK. Noninvasive in vivo human coronary artery lumen and wall imaging using black-blood magnetic resonance imaging. Circulation.1 Aug 2000;102(5):506-10. PMID: 10920061
3. Gradus-Pizlo I, Bigelow B, Mahomed Y, Sawada SG, Rieger K, Feigenbaum H. Left anterior descending coronary artery wall thickness measured by high-frequency transthoracic and epicardial echocardiography includes adventitia. American Journal of Cardiology. January 2003;91(1): 27-32
4. Velican C and Velican, D. Progression of coronary atherosclerosis from adolescents to mature adults. Atherosclerosis 1983;47(2):131-144
5. Joshi AK; Leask RL; Myers JG; Ojha M; Butany J; Ethier CR. Intimal Thickness Is not Associated With Wall Shear Stress Patterns in the Human Right Coronary Artery.Arteriosclerosis, Thrombosis, and Vascular Biology. 2004;24:2408-2413
6. Junqueira LC, Carneiro J. Basic histology: text and atlas. 12th ed. New York: McGraw-Hill 2010; p: 360-65.
7. Levy AD, Harcke, HT Mallak, Craig T. Postmortem Imaging: MDCT Features of Postmortem Change and Decomposition American Journal of Forensic Medicine and Pathology: March 2010;31(1):12-17.
8. Bancroft JD, Gamble M. Theory and Practice of Histological Techniques. 5th ed. London, England: Churchill-Livingstone 2002.
9. Siegel RJ, Swan K, Edwalds G, Fishbein MC. Limitations of postmortem assessment of human coronary artery size and luminal narrowing: differential effects of tissue fixation and processing on vessels with different degrees of atherosclerosis. J Am Coll Cardiol. Feb1985;5(2 Pt 1):342-6. PMID: 3881498
10. Neufeld HN, Schneeweiss A. Coronary Artery Disease in Infants and Children. Lea and Febiger, Philadelphia 1983; 1-28.
11. Podesser BK, Neumann F, Neumann M, Schreiner W, Wollenek G, Mallinger R. Outer Radius-Wall Thickness Ratio, a Postmortem Quantitative Histology in Human Coronary Arteries. Acta Anatomica 1998;163: 63-68.
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|Author:||Ullah, Qazi Waheed; Qamar, Khadija; Butt, Shadab Ahmed|
|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Mar 31, 2012|
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