a cadaveric study on muscle bridges in human hearts

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http://www.eternalpublication.com IJAPB: Volume: 2; Issue: 3; March 2015 ISSN(Online):2394-3440 A Cadaveric study on Muscle Bridges in human hearts

Published online on 1st March 2015©www.eternalpublication.com ———————————————————————————————————————————————————————————————————

DR. CHANDRASEKHAR KT 1

DR. HARSHA BR 2

1Assistant Professor, Department of Anatomy, MMC&RI, Mysore, Karnataka. 2Assistant Professor, Department of Anatomy, CIMS, Chamarajanagar, Karnataka. Corresponding Author:

Received: 6th Feb 2015; Accepted: 18th Feb 2015

How to cite this article: Chandrasekhar KT, Harsha BR. A cadaveric study on muscle bridges in human hearts. International Journal of Anatomy Physiology and Biochemistry 2015; 2(3):1-6.

Abstract: Background: Muscle bridge/ myocardial bridge are structures consisting of heart muscle tissue which pass above the coronary arteries and their branches. The frequency of myocardial bridging varies widely. Myocardial bridge has been considered a benign condition, but the various complications have been reported. Thus in view of its complication, myocardial bridge should be considered an anatomical risk factor in evaluating coronary artery disease. There is a wide variation in percent of hearts showing myocardial bridges in every study reported. All these factors made to take up the present study, and perform detailed anatomical study of myocardial bridge in human heart. Materials and Methods: Study was carried out on 50 normal formalin fixed human heart specimens. Dissection was performed according to standard techniques. The percentage of hearts showing myocardial bridges, the distribution of myocardial bridges over the different branches of the coronary arteries were observed and documented. Results: Myocardial bridges (MB) were found in 35 (70%) of the hearts with a total of 46 bridges. Single bridge was found in 25 of these hearts and multiple bridges were observed in 10 (9 with double bridges and 1 with triple bridges).They were most often found over the anterior interventricular artery (28 MB), on its middle third (20 MB). Bridges were also found over the diagonal branch (4 MB) and over the left marginal branch (3 MB) branch of the left coronary artery. Out of 11MB found over the right coronary artery, 5 MB was found over the first segment and 6 MB over the posterior interventricular branch of the right coronary artery. Conclusion: The present study adds up the information regarding the prevalence, relationship of myocardial bridges to coronary arteries.. The possibility of myocardial bridges should be borne in mind in individuals with ischemia but no evidence of coronary atherosclerosis. Keywords: anterior interventricular artery, coronary artery, left anterior descending artery, myocardial bridge

Introduction: Human heart is one of the vital organs of our body. The blood supply to the heart is always of interest to

Dr. Chandrasekhar KT. Assistant Professor Department of Anatomy MMC&RI Mysore-570001(Karnataka, India)

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[email protected]

ORIGINAL RESEARCH ARTICLE

INTERNATIONAL JOURNAL OF ANATOMY PHYSIOLOGY AND BIOCHEMISTRY

IJAPB: Volume: 2; Issue: 3; March 2015 Original Article ISSN(Online):2394-3440

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every medical person, as in the present clinical scenario, most of the disease process affects the arteries directly or indirectly. The first description of myocardial bridge dates from 1737 – Reymann1 who observed that segments of the left coronary artery can be covered with a thin layer of heart muscle fiber.

Muscle bridge/ myocardial bridge are structures consisting of heart muscle tissue which pass above the coronary arteries and their branches. The coronary arteries and their major branches travel along the surface of heart under the epicardium. However occasionally a portion of these arteries may be embedded in muscle, finding that has been variously described as a mural coronary artery, submerged coronary artery, tunneled artery or more frequently myocardial bridge.2,3

The epicardial cells undergo epithelial-to-mesenchymal transition controlled by factors from the myocardium. The mesenchymal cells thus formed migrate through the spaces generated in the developing myocardium finally forming the coronary arterial system. This migration of these mesenchymal cells through the developing myocardium could explain the embryogenesis of myocardial bridges over the portions of coronary arteries.4

Myocardial bridge is a congenital anomaly characterised by narrowing during systole and some of epicardial arterial segment running in the myocardium.5

Myocardial bridge has been considered a benign condition, but the following complications have been reported: ischemia and acute coronary syndrome, coronary spasm, ventricular septal rupture, arrhythmias (including supraventricular tachycardia and ventricular tachycardia), exercise induced atrio-ventricular conduction block, stunning, transient ventricular dysfunction, early death after cardiac transplantation and sudden death.6

Bridging of coronary arteries in otherwise angiographically normal arteries generally is not hazardous to the patient. However strenuous physical exertion results in compression of a portion of a coronary artery by a myocardial bridge.7

The degree of coronary obstruction by a myocardial bridge depends on factors such as location, thickness, length of muscle bridge, and degree of contractility. Thus in view of its above complication, myocardial bridge should be considered an anatomical risk factor in evaluating coronary artery disease. There is a wide variation in percent of hearts showing myocardial bridges in every study reported. All these factors made to take up the present study, and perform detailed anatomical study of myocardial bridge in human heart by dissection method.

Materials and Methods:

The study was carried out on 50 formalin fixed human hearts from patients who had died of non-vascular causes and were autopsied. Specimens with injury or underwent any surgical procedure on coronary arteries and with gross abnormality were rejected. After exploring the pericardial cavity, the heart was detached from the major venous channels (superior vena cava and inferior vena cava) and the aorta was cut 3 centimetres above the level of the coronary sinus and then the heart was extracted with intact epicardium and coronary vessels. The specimens were stored in 10% formalin solution. The right and left coronary arteries were traced carefully from its origin to its most distal end by cleaning the epicardium and fat piecemeal using blunt and pointed forceps. The left coronary artery along with its branches was dissected as it passed between the auricle and pulmonary trunk and was followed to its most distal end. The right coronary artery along with its branches were also dissected and followed to its distal end. The presence, location and the length of myocardial bridges was noted with the part of the artery and or its branch it was crossing. Specimens showing the myocardial


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bridges were photographed from various angles and were numbered.

Observations and Results:

Out of 50 heart specimens, 35 heart specimens (70%) showed the presence of myocardial bridges. In which Twenty five (71.43%) hearts showed single bridge, nine (25.71%) hearts presented with double bridge and one heart (2.86) had triple bridge out of 35 hearts. Thus out of 35 hearts 46 myocardial bridges (MB) were present. Out of total 35 hearts with myocardial bridges, 6 (17.14%) showed MB on the right coronary artery only, 24 (68.57%) showed MB on the left coronary artery only and 5 (14.29%) showed MB on both the right and left coronary artery. Out of 46 total myocardial bridges, maximum number 20 (43.49%) of MB were present in middle segment of anterior interventricular branch of left coronary artery, 7 (15.23%) MB was present on the proximal segment of anterior interventricular branch of left coronary artery, 4 (8.69%) MB was present on the left diagonal and 3 (6.52%) MB was present on the left marginal branch of left coronary artery. On the first segment of right coronary artery 5 (10.87%) MB and on the posterior interventricular branch of right coronary artery 6 (13.04%) MB was present. Least number of MB were noted on distal 1/3rd of anterior interventricular branch of left coronary artery which was 2.17% (1 out of 46).Out of 28 MB on, maximum number of MB were present on the middle 1/3rd i.e. 20 (71.43%), 7 (25%) MB were present on the proximal 1/3rd and 1 (3.57%) MB was present on the distal 1/3rd of anterior interventricular branch of LCA which was statistically significant (p value < 0.0001).

Figure 1: Single Myocardial bridge (MB) in the anterior interventricular (AIV) branch of left coronary artery (LCA).

Figure 2: Showing double MB over AIV branch of LCA

Figure 3: Showing triple MB, two MB over AIV branch of LCA.


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Figure 4: Showing triple MB, one MB over posterior interventricular (PIV) branch of right coronary artery (RCA).

Discussion:

Table 1: The Prevalence of Muscular bridges

Sr No

Study Sample Size

Prevalence of MB (%)

Comment

AUTOPSY METHOD

1 Geiringer E6 100 23 AIV

2 Polacek7 70 86 AIV- 60%

3 Lee and Wu9 108 58 AIV

4 Ferreira AG Jr et al8

90 56 All coronaries

5 Baptista & DiDio11

82 54 All coronaries, 35% in AIV

6 Kosinski & Grzybiak2


7 Present study


ANGIOGRAPHIC METHOD

8 Angelini et al12

1100 4.5 All patients

9 Harikrishnan et al13


10 Mavi A et al14


The prevalence varies substantially among studies with a much higher rate at autopsy versus angiography. Variation at autopsy may in part be attributable to the care taken at preparation and the selection of hearts. Polacek7 who included myocardial loops, reports the highest rate with bridges or loops in 86% of cases. The prevalence of myocardial bridges in the present study is 70% which is less than Polacek10 but more than other studies.

Myocardial bridges were more frequently found on male hearts in the present study which is even supported by Ferreira AG Jr8 1991, Kosinski A2 2004, Loukas15 2006.

Observation was made on the number of myocardial bridges on the hearts in the present study. Geiringer6 1951 did not observe double and triple MB, the analyses of majority of investigators tabulated below and our own observation confirms that these can potentially occur either over one or more coronary arteries.

Table 2: Comparison of number of myocardial bridges in the hearts with other studies

SrNo

Studies No. of hearts studied

No. of hearts with MB (%)

Total no. of bridges

Hearts with myocardial bridges (MB)

Single Double Triple

1 Present study

50 35 (70%)

46 25 (50%)

9 (18%)

1 (2%)

2 Ferreira AG et al8

90 50 (55.6%)

70

35 (38.9%)

10 (11.1%)

5 (5.5%)

3 Kosinski A et al2

300 94 (33.3%)

114 75 (24.9%)

18 (5.9%)

1 (0.3%)


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4 Loukas M et al15

200 69 (34.5%)

81 59 (29.5%)

8 (4%) 2 (1%)

All the studies tabulated above showed the single MB in majority of cases followed by double and triple MB. But the percentages of MB are high in the present study when compared with others.

Apart from the studies above, authors like Bapista and Didio11 found double MB in 6 hearts but related only to anterior interventricular branch of left coronary artery. Voelkar et al17 observed 3 MB in one heart which was over anterior interventricular artery, left diagonal and left marginal branch of left coronary artery during coronary angiography. In the present study we observed double MB in 9 hearts, out of which 1 heart had MB over same artery (AIV branch of left coronary artery) and other 8 hearts had MB over different branches of coronary arteries. We also observed triple MB in 1 heart over posterior interventricular branch of right coronary artery, proximal 1/3rd and distal 1/3rd of AIV branch of left coronary artery.

In the light of previous studies by Ferreira AG8 1991, Vanildo Junior de Melo Lima18 2002, Kosinski A2 2004, AyferMavi et al14 2008, MB are most often associated with the left coronary artery on AIV, mainly the middle 1/3rd of this. These results are consistent with our observation. The searching for the nature of this coexistence should probably focus on analysis of the processes connected with the development of the coronary vessels during foetal life. The formation of superficial arterial system begins between 5 and 6 weeks after fertilization and before the development of the myocardium has been completed. It is likely that the coincidence of these processes is a prerequisite for a MB arising. The earlier development of the artery leads to a greater probability of some fibres of the myocardium forming a MB over it. Initially arteries occur in grooves along the places with maximum concentration of connective tissue. The AIV stands

apart as the first and MB are observed most frequently over this artery.

Vanildo Junior de Melo Lima18 2002 also did not found MB on distal 1/3rd of AIV but we observed MB over this in our study.

The current study found that the next most common sites of myocardial bridges were over the proximal 1/3rd of anterior interventricular artery (15%) followed by posterior interventricular branch of right coronary artery (13.04%), Ist segment of right coronary artery (10.87%), the diagonal branch of the left coronary artery (8.69%), the left marginal branch (6.52%). However, whereas Kosinski A et al2 (2004) reported the AIV as the most common site for bridges in a study of 300 specimens, he also reported that the diagonal branch of the left coronary artery was the second most common site and the posterior interventricular branch of the right coronary artery the third most common.

We have showed the distribution of hearts having MB in both RCA and LCA which was not commented in the study of these authors.

Conclusion:

Muscle bridges are still an open issue. The discussion whether it is pathology or a variation of physiology is still ongoing. It is known that their existence is congenital. In the present study, we have tried to find out the prevalence, over coronary arteries and the relationship of myocardial bridges to coronary artery dominance in the adult human hearts. In most of the individuals they do not cause symptoms but particularly in those with long and deep myocardial bridges, the anatomical relation of the myocardial fibres can distort the artery that can be identified angiographically. The possibility of myocardial bridges should be borne in mind in individuals with ischaemia but no evidence of coronary atherosclerosis.

References:


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1. Reymann HC. Disertatio de vasiscordispropriis. Med Diss Univ Gottingen 1737:1-32.

2. Kosinski A, Grzybiak M, Skwarek M, Hreczecha J. Distribution of muscular bridges in the adult human heart. Folia Morphol 2004;63(4):491-8.

3. Soran O, Pamir G, Erol C, Kockavak C, Sabah I. The incidence and significance of myocardial bridge in a prospectively defined population of patients undergoing coronary angiography for chest pain. Tokai J Exp Clin Med 2000;25(2):57-60.

4. Alegria JR, Herrmann J, Holmes DR Jr, Lerman A, Rihal CS. Myocardial bridging. European Heart Journal 2005;26:1159-68.

5. Cotlar JM. Myocardial bridging. J Insur Med 2004;36:335-38.

6. Geiringer E. The mural coronary artery. Am Heart J 1951;41:359-68.

7. Polacek P, Kralove H. Relation of myocardial bridges and loops on the coronary arteries to coronary occlusions. Am Heart J 1961;61:44-52.

8. Ferreira AG Jr, Trotter SE, Konig B Jr, Decourt LV, Fox K, Oslen E G J. Myocardial bridges: morphological and functional aspects. British Heart J 1991;66:364.

9. Lee SS, Wu TL. The role of the mural coronary artery in prevention of coronary atherosclerosis. Arch Pathol 1972;93:32-5.

10. Naczyn PBS, Im OKS, Poznaniu SJ. Intracoronary stent implantation for treatment of myocardial ischemia induced by myocardial bridge-A case report. Polish Heart J 1998;48:6.

11. Baptisda CAC, DiDio LJA. The relationship between the directions of myocardial bridges and the branches of the coronary arteries in the human heart. SurgRadiolAnat 1992;14:137-40.

12. Angelini P, Tivellato M, Donis J, et al.Myocardial bridges: a review. Prog Cardiovasc Dis. 1983;26:75-88.

13. Harikrishnan S, Sunder KR, Thakaran J, Titus T, Bhat A, Sivasankaran S, et al. Clinical and angiographic profile and follow up of

myocardial bridges: A study of 21 cases. Indian Heart J 1991;51(5):503-7.

14. Mavi A, Sercelik A, Ayalp R, Karben Z, Batyraliev T, Gumusburun E. The angiographic aspects of myocardial bridges in Turkish patients who have undergone coronary angiography. Ann Acad Med Singapore 2008;37:49-53.

15. Loukas M, Curry B, Bowers M, Louis RG, Bartozak A, Kiedrowski M, et al. The relationship of myocardial bridges to coronary artery dominance in adult human heart. Journal of Anatomy 2006;209:43-50.

16. Mohlenkamp S, Hort W, Ge J, Erbel R. Update on myocardial bridging. Circulation 2002;106(20):6-11.

17. Voelkar W, Schick KD, Karsch KR. Myocardial bridges at multiple sites over left coronary artery in a patient with hypertrophic cardiomyopathy. Int J Cardiol 1989;23:258-60.

18. Vanildo Junior de Melo Lima, Cavalcanti JS, Tashiro T. Myocardial bridges and their relationship to the anterior interventricular branch of the left coronary artery. Arq Bras Cardiol 2002;79(3):219-22.

a cadaveric study on muscle bridges in human hearts

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