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Anatomy & distribution of coronary arteries in pig in comparison with man.

Background & objectives: The suitability of pig as an animal model for research in coronary artery disease is well established. As coronary arteries (CAs) of the pig are reportedly closely resemble those of man. We investigated the CAs of the pig (Sus scrofa) and study differences between the two, if any.

Methods: The origin and pattern of the coronary arteries were studied in the hearts of 30 fully grown pigs obtained from a slaughter house in Chandigarh (India). The openings of the CAs were identified at the commencement of the ascending aorta. The arteries were washed with acetone by introducing appropriate sized cannulae in their ostia. A 20 per cent solution of cellulose acetate butyrate (CAB), a plastic material, dissolved in acetone was injected in the CAs. The hearts were fixed in 10 per cent formalin solution for three to four days after which the CAs and their branches were dissected.

Results: Both coronary arteries arose from the aortic sinuses below the supravalvular ridge in all the cases. Sinuatrial nodal artery (SAN) arose from the RCA in 70 per cent and from the circumflex artery (CX) in 30 per cent of instances. There was RCA dominance in all hearts of the pig. The atrioventricular nodal artery (AVN) and the posterior interventricular artery (PIV) were branches of RCA. The coronary arterial circulation in the pig was found to be similar to that in human.

Interpretation & conclusions: By and large the coronary arterial pattern of the pig was similar in that of the humans. We can conclude that the heart of a pig can be used for experiments but differences have to be kept in mind.

Key words Comparison - coronary arteries - heart - man - pig

Literature available on the coronary arteries (CAs) of the pig (Sus scrofa) is meagre. The pattern of the CAs in the pig was similar to that of the humans and the right coronary artery (RCA) was the dominant artery (1-3).

Comparison between the distribution patterns of CAs in pig and man has not been studied. In India, no investigation seems to have been conducted on CAs of the pig. We carried out this study to assess the coronary arterial pattern in the pig (Sus scrofa), and an attempt was made to compare it with those of our findings in the human heart (4-8) to elucidate the, differences, if any, in the pattern of CAs in the two species.

Material & Methods

The study was conducted in the Department of Anatomy, Postgraduate Institute of Medical Education & Research, Chandigarh, on 30 hearts of domesticated pigs. The hearts were obtained from a slaughter house in Chandigarh, India. The hearts were intact without any injury to blood vessels. The animals were fully grown but their weight, age and sex were not known. Each heart was washed under running tap water as in the case of human heart (4). After a gross inspection of each heart, the openings of the CAs were identified at the commencement of the ascending aorta. The arteries were washed with acetone by introducing appropriate sized cannulae in their ostia. A 20 per cent solution of cellulose acetate butyrate (CAB), a plastic material dissolved in acetone was injected in the CAs (4). The hearts were fixed in 10 per cent formalin solution for three to four days. Fat and connective tissues surrounding the CAs and their branches were carefully dissected without injuring the blood vessels. The interventricular septum (IVS) was exposed as in human hearts (6), the septal arteries (perforators) running subendocardially were dissected. The study protocol was approved by the Ethics committee of the Institute.

Results

Right coronary artery (RCA)

The RCA arose from the middle of the anterior aortic sinus below the supravalvular ridge in all specimens. After origin, it extended to the right behind the pulmonary trunk and thereafter between the pulmonary trunk and the right atrium and then in the right anterior atrioventricular sulcus to reach the acute margin of the heart, where it turned around to lie in the posterior atrioventricular sulcus (Fig. 1). The portion of the artery which was lying in the anterior atrioventricular sulcus was called the first segment while the part lying in the posterior atrioventricular sulcus was named the second segment. About 5 mm proximal to the crux, the artery turned downwards and to the left describing a curve (Fig. 2, see arrow), the convexity of which was directed upwards and to the left. This curve was present in all the hearts. Beyond the curve the artery extended in the posterior interventricular sulcus, where it constituted the third segment. Extending in that for three-fourths of the distance between the crux and the apex, it divided into two branches the right and the left. The right branch extended on the posterior surface of the right ventricle while the left branch either continued in the posterior interventricular sulcus or on the posterior surface of the left ventricle (Fig. 2). There was no visible surface anastomosis between the terminal branches of this artery and the ventricular branches of the left coronary artery (LCA).

Branches from the first segment

Sinuatrial nodal artery (SAN): In 21 (70%) hearts the SAN artery arose as the first branch from its right side at a mean distance of 20 mm distal to the origin of the RCA (Fig. 1). It extended upwards and to the left on the surface of the right atrium to reach the S.A. node between the right atrial appendage (RAA) and the superior vena cava (SVC).

Atrial branches: One to three atrial branches arose from the right side of the RCA and extended upwards and to the right on the anterior surface of the right atrium. They were very small branches. There was no visible anastomosis between them.

Right conus artery (RC): It was the first but a small branch which arose from the left side of the RCA and extended to the left on the anterior surface of the right ventricle. It did not show any anastomosis with a similar left coronary branch. Hence, there was no anastomotic circle around the pulmonary trunk ('annulus of Vieussens').There was no third coronary artery arising directly from the aorta.

Ventricular branches (VB) : Three to four ventricular branches arose from the left side of the RCA and passed to the anterior surface of the right ventricle; they descended obliquely downwards and to the left towards the incisura (Fig. 3). There were no gross anastomosis seen between them and the branches of the anterior interventricular artery (AIV).

Acute marginal branch (AM): On reaching the acute margin of the heart, the RCA gave a small marginal branch which extended to the left towards the apex (Fig. 3). It did not show any anastomosis with the branches of the AIV.

No specimen showed the middle or a posterior border branches.

Branches from the second segment

Atrial branches: Usually, there were two to three atrial branches which extended upwards from the second segment to the posterior surface of the right atrium. Ventricular branches (Fig. 2): This segment also gave three to four short ventricular branches (VB) which extended downwards and to the right on the posterior surface of the right ventricle.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

A. V. nodal artery (AVN): An AVN artery arose separately or jointly with the left atrioventricular sulcal branch (SB) from the convexity of RCA near the crux of the heart, the AVN artery could be traced to the AV node. The sulcal branch passed to the left in the posterior atrioventricular sulcus and might anastomose with the sulcal branch of the circumflex artery (CX).

Branches from the third segment

Posterior interventricular artery--Ventricular branches: Three or four obliquely directed ventricular branches arose from the right side of the third segment of RCA and extended downwards and to the right and passed on the posterior surface of the right ventricle (Fig .2). Small septal perforators arose from the deeper surface of posterior interventricularartery.

Left coronary artery (LCA)

In all instances, LCA arose from the left posterior aortic sinus and extended to the left behind the pulmonary trunk for a mean distance of 5 mm and divided into anterior interventricular and CX arteries (Fig. 4).

Anterior interventricular artery (AIV)

It passed in the anterior interventricular sulcus usually for three or fourths of its length when it divided into two terminal branches (Fig. 5). In four hearts, the AIV terminated as three to four branches near the incisura on the acute margin. There seemed to be anastomosis between the right terminal branches of the AIV and ventricular branches of the first segment of RCA including the acute marginal artery.

Branches from AIV (Figs 4 & 5): A left conus (LC) branch and three to four short ventricular branches arose from the right side of the AIV. The conus artery was the first branch. It was a short artery; it did not show any anastomosis with the conus artery of the RCA. Three to four diagonally directed branches also arose from the left side of AIV and continued on the anterior surface of the left ventricle. One of them usually the upper could be long and considered to be the diagonal artery (DB). Septal perforators also arose from its deeper aspect.

Circumflex artery (CX)

After origin, it continued in the left anterior atrioventricular sulcus to reach the obtuse margin of the heart (Fig. 6), crossing the same it passed in the left posterior atrioventricular sulcus usually for half the distance between the obtuse margin and the crux, where it divided into a sulcal branch and a ventricular branch (Fig. 2). The former usually anastomosed with the sulcal branch of RCA while the later extended downwards on the posterior surface of the left ventricle. The part of the artery lying in the anterior atrioventricular sulcus was called the first segment while the portion lying in the posterior part of the atrioventricular sulcus was named the second segment.

Branches from the first segment of circumflex artery

S.A. nodal (SAN) artery: The SAN artery was found to arise from the upper border of proximal part of the CX in 9 of the 30 hearts (30%). After origin, it ran upwards and to the right on the anterior surface of the left atrium behind the aorta and pulmonary trunk to reach the S.A. node (Fig. 6).

Atrial arteries: There were one to two atrial branches which arose from its upper border. They ran upwards on the anterior surface of the left atrium to supply the same.

Ventricular branches: One to two ventricular branches arose from its lower border; they passed downwards on the anterior surface of the left ventricle.

Diagonal branch : In 50 per cent hearts a long diagonal branch extended on the anterior surface of the left ventricle towards the apex of the heart.

Obtuse marginal branch (OM): The obtuse marginal branch was seen in 90 per cent hearts. It extended along the obtuse margin of the left ventricle (Fig. 5)

Branches from the second segment of circumflex artery (Fig. 2)

One to two atrial branches arose from its upper border and passed upwards on the posterior surface of the left atrium. Two to four ventricular branches arose from the lower border of the CX which extended on the posterior surface of the left ventricle. In four instances even six ventricular branches were also seen.

There was RCA dominance in all the specimens (100%).

Blood supply to the interventrieular septum

As in human heart septal branches which may be called as perforators arose from the anterior and posterior interventricular arteries. Anterior interventricular artery was a branch of LCA while the posterior was that of RCA in all instances.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Perforators from the anterior interventricular artery (AIV)

The origin of the first anterior perforator was very constant; it arose from the deeper surface of the AIV, a branch of the LCA, at approximately 15 mm from the origin of the later. It extended across the posterior wall of the infundibulum of the right ventricle. In the interventricular septum it divided into number of branches (Fig. 7). There were five additional small perforators which supplied the septum and anastomosed with the perforators from PIV in all the hearts.

Perforators from the posterior interventricular artery (PIV)

Nine or ten small perforators arose from the deeper surface of PIV. They extended anteriorly in the septum as perforators and anastomosed with the perforators from AIV (Fig. 8).

Discussion

The prospect of using pig organs for human xenotransplantation is becoming increasingly likely due to advances in the transgenic technology. Futhermore, pigs share important characteristics with the anatomy of human cardiovascular system, making them useful models for the study of human diseases. Comparative morphological studies on the coronary arteries of the left ventricular free wall were carded out on human, dog, and monkey hearts by using postmortem coronary arteriography, soft X-ray photograms, and the clearing method. The results showed that the types of coronary arteries (types I, II, and III) and connecting portion of anastomotic vessels in the pig and monkey hearts closely resembled those in man (9). With this in mind we discuss the anatomy and distribution of coronary arteries of the porcine heart and compared the same to that of our earlier study in man (4-6). The study showed that the distribution and branching of the CAs in the pig heart appeared about the same and similar to earlier general descriptions given in the literature except some variations observed in the present study.

Trifurcation of LCA: The division of the LCA into three branches-AIV, CX and an intermedium branch had been observed previously in 20 per cent cases (10), such a variation has neither been seen in the present study nor has been mentioned by any other author.

Dominance: Variation in the total cardiac supply mainly affects the diaphragmatic surface of the heart as the posterior surfaces of the both ventricles consist of the relative 'dominance' of blood supply of a branch from RCA or LCA. Although the term is misleading as the LCA supplies a greater volume of heart tissue, yet the most acceptable definition of 'dominance' is designated as the coronary artery which extends in the posterior interventricular sulcus. In 'right dominance' the PIV is derived from the RCA, in 'left dominance' it is from the LCA and in 'balanced' circulation branches of both arteries in or near the groove. In the present study, consisting of 30 specimens, the RCA was always seen to extend as the PIV and extended along the entire posterior length of interventricular sulcus. This is in agreement with the observations of earlier authors (1,2) but in contradiction to Weaver et al (10) who found dominance of RCA in 78 per cent and LCA in 5 per cent and balanced circulation in 17 per cent swine hearts.

Intercoronary anastomosis: Blumgart et al (1) studied the coronary arteries of 44 pigs and did not find any visible intercoronary anastomoses in 43 hearts. However, in one heart inter-communicating twigs were seen between left anterior descending and branches of RCA at the apex. In the present study, surface anastomosis was hardly observed which is in confirmation with the observations of earlier authors.

Comparison between the pattern of distribution of the coronary arteries of the pig and man: On comparing the observations of the pattern of distribution of CAs in the pig to that of man (4-8), it was found that the pattern was almost similar to the later except some gross percentage frequency differences. In all instances in pig's heart both CAs arose from the sinus below the supravalvular ridge, however, in the human hearts the RCA arose below the supravalvular ridge in 85 per cent of males and 87 per cent of females; the LCA arose from the sinus in 67.8 per cent of males and 71.3 per cent of female (5). In the pig the SAN arose from the RCA in 70 per cent instances while the incidence in human was 74.7 per cent in male and 68 per cent female hearts (4). The acute marginal artery arising from RCA was present in 60 per cent hearts of the pig; 87 per cent in male and 90 per cent in female hearts in the humans. It has been emphasized that the coronary arterial circulation of the pig is remarkably similar to man (1-3,10,11).

Our observations, have demonstrated some significant differences in the coronary circulation of pig and human hearts; recognition of these differences is important for the surgeons. The main differences in the pattern of CAs of the pig from that of man was that the third coronary artery and the border branches were not seen in any of the specimen in the former. The posterior interventricular artery was always a branch of RCA in the hearts of pig hence there was 100 per cent RCA dominance which was not so in human hearts. Besides this, AIV terminated proximal to apex in the pig hearts while in human hearts it usually crossed the apex. The origin and course of both the anterior and posterior septal arteries were similar to the analogous arteries in the human heart except that posterior perforators were always from the RCA in pig's heart. In about 85 per cent of human hearts the RCA or its conus branch gave an interventricular septal branch, which established anastomoses with the septal perforators of AIV; this artery was not seen in the hearts of pig.

In conclusion, as far as the coronary blood supply is concerned the heart of the pig was similar to that of man with small differences. Therefore, pig's heart could be used for conducting experiments on coronary arteries.

Acknowledgment

Authors thank the Director of the Postgraduate Institute of Medical Education and Research, Chandigarh, for financial support.

Received April 23, 2007

References

(1.) Blumgart HL, Zoll PM, Freedberg AS, Gilligan DR. The experimental production of intercoronary arterial anastomoses and their functional significance. Circ J 1950; 10:10-27.

(2.) Lumb G, Singletary HE Blood supply to the antrioventricular node and bundle of His: A comparative study in pig, dog, and man. Am J Pathol 1962; 41 : 65-71.

(3.) Schwarze E, Schroder L. Kompendium der Veterinar Anatomie, Band III Jena, VEB Gustav Fisher Verlag 1964.

(4.) Sahni D, Jit I. Sinuatrial nodal artery in the north-west Indians. Indian Heart J 1988; 40 : 29-36.

(5.) Sahni D, Jit I. Origin and size of the coronary arteries in the north-west Indians. Indian Heart J 1989; 41 : 221-8.

(6.) Sahni D, Jit I. Blood supply of the human interventricular septum in north-west Indians. Indian Heart J 1990; 42 : 161-9.

(7.) Sahni D, Jit I. Size of the valves and thicknesses of anterior walls of the ventricles of the adult Indian hearts. Indian Heart J 1991; 43 : 361-5.

(8.) Sahni D, Jit I. Incidence of myocardial bridges in north-west Indians. Indian Heart J 1991; 43 : 431-6.

(9.) Kato T, Yasue T, Shoji Y, Shimabukuro S, Ito Y, Goto S, et al. Angiographic difference in coronary artery of man, dog, pig, and monkey. Acta Pathol Jpn 1987; 37 : 361-73.

(10.) Weaver ME, Pantely GA, Bristow JD, Ladely HD. A quantitative study of the anatomy distribution of coronary arteries in swine in comparison with other animals and man. Cardiovasc Res 1986; 20 : 907-17

(11.) Christensen GC, Campeti FL. Anatomic and functional studies of the coronary circulation in the dog and pig. Am J Vet Res 1959; 20 : 18-26.

Reprint requests: Dr Daisy Sahni, Additional Professor, Department of Anatomy, Postgraduate Institute of Medical Education & Research, Chandigarh 160 012, India e-mail: daisy_sahni@rediffmail.com

Daisy Sahni, G.D. Kaur, Harjeet & Indar Jit *

Department of Anatomy, Postgraduate Institute of Medical Education & Research, Chandigarh, India

* Late Emeritus Professor, Department of Anatomy, Postgraduate Institute of Medical Education & Research, Chandigarh 160 012, India
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Author:Sanhi, Daisy; Kaur, G.D.; Jit, Harjeet; Jit, Indar
Publication:Indian Journal of Medical Research
Article Type:Clinical report
Geographic Code:9INDI
Date:Jun 1, 2008
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