European Journal of Cardiovascular Medicine

Nowadays coronary artery disease is one of the major causes of death in developing countries.¹ Congenital, inflammatory, metabolic and degenerative diseases may affect the coronary circulations. So to combat with this problem much more progress has been made in last few decades than in all forgoing medical history in the management of cardiovascular diseases. Presence of even minor variations may lead to considerable amount of mortality and morbidity among patients when encountered during surgery.

Recently myocardial bridges (MB) have received attention of clinicians. There is large amount of literature available on myocardial bridge descriptions but researchers do not present uniform attitude towards the phenomenon.² Noble et al.,³ described the milking effect and put forward the hypothesis that myocardial bridge may be the cause of myocardial ischemia. Most of scientists agree that the existence of myocardial bridges can significantly modulate the hemodynamic phenomenon. There are also reports suggesting that the bridge may influence the dynamics of sclerotic changes and cause deficit of myocardial bridge during high heart rate.⁴ Also the angiographic appearance at the site of myocardial bridge show distortion resembling focal disease process and could result in misinterpretations in coronary angiographies.⁵

Literature regarding coronary artery circulation is continuously enriched in order to avoid wrong interpretation of coronary angiographies, assessment of findings of coronary insufficiency, understanding the functional disturbances of heart in coronary artery disease and to improve surgical outcome in management of congenital and acquired heart disease and myocardial revascularization. Present study was aimed to study coronary dominance and myocardial bridges in human cadaveric hearts.

Present study was prospective, observational study, conducted in department of anatomy, at Govt. medical college, Miraj, India. Study duration was of 2 years (July 2018 to June 2020). Study was approved by institutional ethical committee.  50 adult human hearts fixed in 10% formalin were obtained from the cadavers in department of anatomy. The age, sex, socioeconomic status, religion or pathologic basis was not known.

Costosternum was resected. The fibrous and serous layers of pericardium were incised longitudinally in the midline extending from the root of the great vessels to the diaphragm. The longitudinal incision was followed by a horizontal incision at its upper and lower end. Aorta was cut open at the arch, pulmonary trunk was cut at the level of bifurcation; superior and inferior venae cavae were transected and pulmonary veins were cut. The heart was removed out of the middle mediastinum. All the specimens collected were serially numbered prior to commencement of the dissection of the hearts.

The right & left coronary arteries were dissected further to study, origin, course and branching pattern of arteries, Pattern of coronary dominance & Presence of myocardial bridges.  All the data was recorded as per the proforma in the master chart. Statistical analysis was done using descriptive statistics.

It was observed that the right coronary artery was found to be bifurcated in 1 (2%) specimen in this study. It was bifurcated into small right conus artery and larger right coronary artery.

The left coronary artery was bifurcated in 29 (58%) specimens, trifurcated in 16 (32%) specimens and showed tetrafurcation in 5 (10%) of the heart specimens. It was observed that SA Nodal artery originated from right coronary artery in 36 (72%) specimens while from circumflex branch of left coronary artery in 14 (28%) specimens.

The AV nodal artery originated from right coronary artery in 40 (80%) specimens and left coronary artery in 10 (20%) specimens. In all specimens, the marginal artery was derived from right coronary artery and the anterior interventricular artery from left coronary artery.

Table: 1 Origin of various branches of right and left coronary arteries.

Posterior interventricular artery was derived from right coronary artery i.e. a case of right dominance in 37 (74%) hearts and from left coronary artery i.e. a case of left dominance  in 9 (18%) hearts while it was the case of codominance (both RCA and LCA giving posterior IV branch) in 4 (8%) specimens.

Table 2: Dominance

Myocardial bridges were seen in 18 (36%) specimens while remaining 32 (64%) did not demonstrate such bridging. Bridging was observed on left coronary artery branches in 14(28%) hearts and on right coronary artery branches in 4 (8%) heart specimens. Thus, amongst the heart specimens showing myocardial bridging, 75% showed exclusively on left coronary artery territory while 25% showed exclusively on right coronary artery.

Myocardial bridging was seen more commonly on anterior interventricular branch in 9 (18%) specimens. Thus 50% of all heart specimens showing the presence of bridging had it on anterior interventricular artery. Incidence of bridging seen on other branches is as follows: marginal artery 4 (8%), posterior interventricular 1 (2%), left circumflex 3 (6%) and left diagonal 3 (6%) heart specimens.

Table 3: Contribution of arteries showing myocardial bridges.

The present study was conducted to see the variation pattern in coronary arteries. All heart specimens had single ostial opening in left posterior aortic sinus except the one heart showing two openings. Gajbe UL et al.,⁶ also got similar findings with all the 30 hearts in their study showing RCA originating from right aortic sinus and LCA originating from left posterior aortic sinus. Joshi SD et al.,⁷ in their study found that 98% (103/105) specimens had single ostial opening in left aortic sinus. Only 2 hearts had dual openings in the left aortic sinus.

Right coronary artery was found to be bifurcated in 1 (2%) specimen in this study. RCA was bifurcated into small right conus artery and larger right coronary artery. This heart specimen also showed the presence of right anterior ventricular branch originating from the right conus artery.

There was no other anterior ventricular branch originating from RCA. The marginal branch of RCA was also not large enough to compensate for the absence of other anterior ventricular branches. As the only ventricular branch was derived from a relatively small lumen right conus artery, if obstructed, there is increased risk of infarction of a larger right ventricular area in such cases.

Wilkins et al.,⁸ reported 0.02% incidence of bifurcation of the main right coronary arterial trunk into anterior interventricular branch and rest of right coronary artery. Koser P et al.,⁹ in their 64-slice CT angiographic study on 700 patients found 1 case (0.1%) where the RCA split into two arteries just after originating from its ostium in the right sinus of Valsalva and termed it as duplication of RCA. Left coronary artery was found to be bifurcated in 29 (58%), trifurcated in 16 (32%) and tetrafurcated in 5 (10%) specimens.

The incidence of bifurcation and trifurcation in this study was found to be differing from that found in some of the studies while it was similar to the findings by Koser P et al.,⁹ and Reig J et al.,¹⁰ A study by Lujinovic et al.,¹¹ found similar type of differences in incidence with dissection method and angiographic method. Tetrafurcation was also found in other studies with Kalbfleisch et al.,¹² finding it in 6% cases and Kalpana R¹ reporting in 11% specimens.

The anatomical and physiological importance of this branching pattern is not well understood from the literature. There could be few advantages of having a trifurcation instead of bifurcation    The importance of any proximal left anterior descending (LAD) lesion in these patients is negated by 33% as two other vessels are there to take care of the rest of the heart.

Dominance of the coronary artery system is determined according to the origin of posterior interventricular artery. Coronary artery systems with posterior interventricular artery originating from right coronary artery (RCA) are defined as right dominant and those originating from left coronary artery (LCA) are defined as left dominant. . Coronary artery systems where posterior interventricular artery is derived from both RCA and LCA or branches from both arteries run in or near the posterior interventricular groove are termed as codominant. In present study posterior interventricular artery was a branch of RCA i.e. a case of right dominance in 37 (74%) specimens, originated from LCA or its branches i.e. a case of left dominance in 9 (18%) specimens while it was a case of codominance in 4 (8%) heart specimens.

Dominance can be a significant determinant of prognosis in acquired coronary artery disease. In most individuals with left dominance the right coronary artery is usually small and often fails to reach the acute (right) margin of heart so that an acute, proximal occlusion could have disastrous consequences, as the potential for rapid development or re- opening of collateral vessels is likely to be diminished. Furthermore, cardiac rhythm may be deranged as the branch passing to atrioventricular node usually arises from the dominant artery, as does that to the sinoatrial node.

Preoperative information about the coronary arterial anatomy and extent of coronary artery disease may be helpful in planning the use of coronary perfusion and other myocardial preservation techniques during surgery in order to reduce the incidence of myocardial infarction.

Intramyocardial course of a coronary artery, which normally has an epicardial course, is referred to as myocardial bridging (MB). The incidence of MB varies greatly and is reported as 0.5% to 2.5% in conventional angiographic studies and 15% to 85% in pathologic studies. Its incidence has been reported between 3.5% and 38.5% in various studies made with 4 or 16-slice CT Angiography. Myocardial bridging is considered as a benign finding and in vast majority of patients does not cause myocardial ischemia. Rarely, it is the cause of acute myocardial infarction, fatal arrhythmias, and sudden death.

In present study, MB was seen in 18 (36%) specimens while remaining 32 (64%) did not demonstrate such bridging. MB was observed in 4 (8%) specimens on RCA branches and in 14 (28%) hearts on LCA branches.

One of the consistent finding in almost all of the studies is the more incidence of affecting anterior interventricular branch. In present study anterior interventricular artery was most commonly affected with 9(18%) heart specimens demonstrating bridging pattern on this artery. Out of the entire heart specimens showing MB, 50% had bridges on the anterior interventricular branch. The findings of present study are more similar to those derived by Loukas M et al.,¹³ In present study bridging was seen in 28% and 8% heart specimens on LCA and RCA respectively and on anterior interventricular branch in 18%.

The knowledge of variation pattern in coronary arteries prevalent in the population and the associated risks or precautions to be taken in the specific condition is of prime importance for a treating surgeon. The findings in this study may favourably add to the sparsely available data of such kind in Indian population.

A case of right dominance was observed in 37 (74%) specimens, left dominance in 9 (18%) specimens while codominance was found in 4 (8%) heart specimens. Dominance can be a significant determinant of prognosis in acquired coronary artery diseases.

Myocardial bridges were seen in 18 (36%) specimens. Bridging was observed in 4 (8%) specimens on RCA branches and in 14 (28%) hearts on LCA branches. Anterior interventricular artery was most commonly affected with 18% heart specimens demonstrating bridging pattern on this artery. Out of the entire heart specimens showing myocardial bridging, 50% had bridges on the anterior interventricular branch.

Conflict of Interest: None to declare

Source of funding: Nil

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