Chapter 9 – The Coronary Arteries




Abstract




A brief reprise of normal coronary artery structure is followed by a discussion of normal anatomical variants of the coronary arteries. The commoner abnormal variants, including origin of the left coronary artery from the pulmonary artery and intramural course of a coronary artery, are described and illustrated, followed by a discussion of coronary fistula and atresia. A section is devoted to the variations in coronary anatomy associated with the commoner forms of congenital heart disease. Coronary arteritis is discussed, chiefly in the context of Kawasaki disease, but polyarteritis and eosinophilic arteritis are also described. Fibromuscular dysplasia is treated in some detail and idiopathic arterial calcification rounds off the chapter.





Chapter 9 The Coronary Arteries




9.1 Introduction


The anatomy of the normal epicardial coronary arteries has already been described in Chapter 1 and their embryological development is reviewed in Chapter 3. The coronary arteries have a fairly consistent basic normal anatomy, but variations do occur that at their most extreme result in disease. The large burden of congenital heart disease carries with it variations in coronary artery anatomy, particularly in those cases with abnormal ventricular outflow tracts, and these variations have implications for the natural history of the diseases as well as having an impact on the approach to their surgical correction. Atherosclerosis, which accounts for so much morbidity and mortality in adult pathology practice, is very rare in children, but other diseases scarcely seen in adults, such as Kawasaki disease, have a disproportionate effect on the coronary circulation.



9.2 Normal Structure


The normal neonatal coronary artery has an endothelial cell layer resting directly on the internal elastic lamina. The tunica media is muscular and contains a few fine elastic fibrils. The tunica adventitia is fibrous, and an external elastic lamina is not well developed. At the origins of the coronary arteries from the aortic sinuses the elastic tissue of the aortic tunica media extends for a variable distance into the tunica media of the proximal coronary arteries, usually for no more than a millimetre or two (Figure 1.76) [1]. During the first few months of life the coronary arteries develop irregular intimal thickenings, most pronounced in the left anterior descending artery and usually in association with arterial branching points. These areas are fibrous and contain elastic fibres and cells (Figure 1.77). There may be associated breaks in the underlying internal elastic lamina. The exact nature of these histological lesions is still debated. Some claim them to be progenitors of atherosclerosis in later life [2], and others suggest that they arise at points of weakness in the vessel wall associated with branching [3]. Similar changes may sometimes be seen in late stillbirths. They become less conspicuous with the growth in size of the vessels.



9.3 Common Normal Variants of the Coronary Arteries


In the normal situation, the coronary arteries arise from the right- and left-facing sinuses of the aortic valve close to the sinotubular junction. The right coronary artery travels downwards and to the right to enter the right atrioventricular groove and, in that location, courses around to the posterior aspect of the heart. It supplies branches to the pulmonary infundibulum and to the sinoatrial node, the right ventricular myocardium and in about 90% of cases supplies the posterior interventricular artery (right dominant circulation) (Figure 9.1A). The left coronary artery branches after a course of a few millimetres from its origin from the aorta to give an anterior descending artery and a circumflex branch, the latter travelling in the left atrioventricular groove to supply a variable amount of the left ventricular myocardium (Figure 9.1B). The coronary arteries exit the aorta at right angles to that vessel, and although both main vessels skirt the pulmonary trunk, they are not compressed between it and any other structure.






(A) Right dominant normal circulation: the right coronary artery supplies the posterior interventricular artery.





(B) Left dominant normal circulation: the left circumflex artery provides the posterior interventricular artery.





(C) Single coronary artery: in this instance the single artery arises from the left sinus and the right coronary artery runs posterior to the aorta.





(D) Origin of the left coronary artery from the right sinus: the left artery runs anterior to the pulmonary trunk before giving of an anterior interventricular artery and continuing around the left side of the heart as the circumflex artery.





(E) Origin of the right coronary artery from the left sinus: the right artery runs posterior to the aorta to reach the right heart. This configuration has similarities to 9.1C, but there are separate orifices for right and left coronary arteries.





(F) Origin of the left anterior descending artery from the right sinus: the vessel runs anterior to the pulmonary trunk.





(G) Origin of the left circumflex artery from the right sinus: the circumflex vessel runs posterior to the aorta. In none of the examples above does any of the coronary arteries run between the aorta and the pulmonary trunk. Contrast with Figure 9.7.



Figure 9.1 Variant coronary artery patterns in the structurally normal heart. Plasticine models of the base of the heart. The pulmonary trunk is to the top of the model and the aorta in the centre of the base of the heart. The atrial walls are not shown. The mitral valve is represented on the left of the model and the tricuspid valve to the right. The proximal course of the epicardial coronary arteries is in red.


A variant of normal is the presence of a single coronary artery, usually arising from the left-facing sinus of the aorta, that then gives rise to all the epicardial arteries (Figure 9.1C). The incidence of an isolated, single coronary artery is noted to be 0.03% of adults referred for coronary arteriography [4]. The incidence of single coronary artery is much higher in patients with congenital heart disease and in particular those with conotruncal malformations: approximately one-third of the cases of isolated coronary arteries have been reported in the setting of transposition of the great vessels and tetralogy of Fallot (Figure 9.2). The single artery may arise from either the right or left sinus of the aortic valve, and the epicardial course is very variable [5].





Figure 9.2 Single coronary artery in congenital heart disease. A case of pulmonary atresia with VSD. A single coronary artery arises from the right sinus of Valsalva and immediately divides into right and left branches. The atretic pulmonary trunk is visible as a fibrous cord to the left of the artery origin


(From Khong TY & Malcolmson RDG (eds) Keeling’s Fetal and Neonatal Pathology. London: Springer; 2015, with permission).

For most of their proximal course the coronary arteries rest on the epicardial surface of the heart. They may dip down into the myocardium for a variable length and to a variable depth before re-emerging onto the epicardial surface (Figure 9.3). The significance, if any, of this myocardial bridging is debated. It is generally not thought to have any pathological significance, except perhaps in the context of hypertrophic cardiomyopathy [6]. Some variations to the above pattern occur so frequently as to be part of the normal spectrum. In about 50% of cases, two, sometimes even three, right coronary arteries arise from the right-facing sinus (Figure 1.42) [7]. The extra vessel is usually small, supplying only a small part of the pulmonary infundibulum and may anastomose with the left coronary system [8].





Figure 9.3 Intramyocardial course of epicardial coronary artery. A case of pulmonary atresia with intact septum. There is no epicardial pulmonary trunk. The left anterior interventricular artery dips into the myocardium from the epicardial surface and emerges more distally where it is crossed by the vein.


One or both of the major coronary arteries may take origin from an inappropriate aortic sinus of Valsalva. The possibilities involve usually only the right- or left-facing sinuses and include origin of both coronaries from the right sinus, origin of both arteries from the left sinus, origin of either the left anterior descending artery or the left circumflex artery from the right sinus, or independent origin of both left anterior descending artery and left circumflex from the left sinus (Figure 9.1DG).


Abnormal origin involving the non-coronary (posterior) sinus is very rare, but possibilities include origin of both right and left coronary arteries from the posterior sinus or origin of either the left or the right artery from the posterior sinus. Of these possibilities, the least uncommon is origin of the right artery from the posterior sinus, a pattern seen with some frequency in transposition of the great arteries [9]. A case is described of right coronary artery arising from the posterior sinus in a normal heart by MRI [10]. The left coronary artery has been described on at least one occasion as arising from the posterior sinus in a normal heart [11].



9.4 Abnormal Variations in the Epicardial Distribution of the Coronary Arteries in the Normally Formed Heart


Abnormalities of origin of the arteries occur with a frequency of about 0.5% in paediatric autopsies [12] and of 1.55% in a large population investigated by angiography [13]. Many forms are described not all of which are pathological.



9.4.1 Anomalous Origin of the Coronary Arteries from the Pulmonary Artery


Among the most serious of the anomalous coronary artery origins is origin of one of the coronary arteries from the pulmonary trunk (Figure 9.4) [14]. The commonest manifestation of this condition is origin of the left coronary artery from one of the sinuses of the pulmonary trunk, usually the left sinus, occasionally the anterior sinus. The right coronary artery in these cases arises normally from the right-facing sinus of the aorta (Figure 9.4). The condition is sometimes referred to by the acronym ALCAPA or Bland–White–Garland syndrome. Much less frequently, both right and left coronary arteries arise from the pulmonary trunk and, even more rarely, may arise from the branch pulmonary arteries.






(A) Model of the abnormality.





(B) On the epicardial surface of the heart the anomalous coronary artery is visible in the left atrioventricular groove and coursing over the anterior wall of the left ventricle. It is dilated and thin-walled.





(C) The right ventricular outflow tract is opened to expose the pulmonary valve. To the right of the picture a coronary artery is seen to arise from the sinus of the valve. On the external surfaces a thin-walled, partially collapsed large artery is visible.





(D) The corresponding view of the left ventricular outflow tract shows the origin of the coronary artery from the right sinus of Valsalva just beneath the sinotubular junction and towards the commissure with the non-coronary cusp, to the right of the field. The left sinus is plainly visible, to the left of the picture, and does not contain a coronary artery orifice.





(E) A four-month-old who died suddenly and at post-mortem an ALCAPA was identified. There was associated dilated cardiomyopathy. The probe is in the left coronary artery orifice as it arises from the pulmonary trunk. The left coronary artery abuts the aorta where it would normally be expected to arise, but there was no communication with the aortic lumen. The right coronary artery can be seen arising normally from the aorta


(From Suvarna SK (ed.) Cardiac Pathology: A Guide to Current Practice. London: Springer; 2013, with permission).


Figure 9.4 Anomalous origin of the left coronary artery from the pulmonary artery.


Origin of the left coronary artery from the pulmonary trunk usually presents in the neonatal period when the perfusion pressure in the pulmonary artery relative to the aorta plummets. This results in myocardial infarction in the area supplied by the left artery. The infant is restless, crying, tachypnoeic, tachycardic and sweaty, and death may ensue from heart failure. If the infant survives, by developing a collateral circulation, the infarcted area scars and the child develops dilated cardiomyopathy and is at risk of sudden death on exertion. Pathologically, the affected left coronary artery is dilated and thin-walled, resembling a vein (Figure 9.4). The left ventricle is enlarged and dilated and, if there has been prolonged survival, there is scarring of the anterolateral wall with fibrosis of the papillary muscles and sometimes calcification. There is endocardial fibroelastosis throughout the left ventricle (Figure 9.5), sometimes also affecting the right ventricle. There may be mitral regurgitation because of ischaemic papillary muscle damage. The intramyocardial branches of the left coronary artery may show intimal thickening (Figure 9.6) [14]. Anomalous origin of the right coronary artery from the pulmonary trunk is much less common than ALCAPA and compatible with normal life.





Figure 9.5 Dilated cardiomyopathy due to ALCAPA. Death in the early teenage years in a case of undiagnosed ALCAPA. The case was thought to be one of dilated cardiomyopathy, and the phenotype is that of DCM with a dilated LV showing EFE


(From Suvarna SK (ed.) Cardiac Pathology: A Guide to Current Practice. London: Springer; 2013, with permission).




Figure 9.6 Intramyocardial coronary arteries in ALCAPA. There is an increase in adventitial collagen, the tunica media is hypertrophied and there is concentric intimal fibroelastic proliferation.


Treatment is surgical and involves either re-implantation of the coronary artery into the aorta or the so-called Takeuchi procedure whereby an aortopulmonary window is created and a patch inserted to create an intrapulmonary tunnel directing aortic blood to the anomalous coronary artery [15]. Those patients who survive the perioperative period have a good prognosis, and cardiac function improves greatly. However, myocardial damage persists and cardiovascular events (arrhythmia, sudden death, heart failure) may occur especially in the post-infantile presentation group [16].



9.4.2 Pathological Anomalous Origin of the Coronary Arteries from the Aorta


The clinical significance of anomalous origin of the coronary arteries depends principally on two factors, the obliquity of the course of the vessel through the aortic wall and on whether or not the coronary artery courses between the aorta and the pulmonary artery (Figure 9.7), both of which factors may result in compression of the vessel [17]. Such abnormalities have been linked to sudden death [18].






(A) Origin of the left anterior descending (LAD) artery from the right sinus. The proximal LAD runs between the aorta and pulmonary artery where there is a theoretical risk of compression. Probably of more significance is the acute angle of origin from the aorta.





(B) Origin of the right artery from the left sinus.





(C) The left main stem rather than just the LAD takes origin from the right sinus.



Figure 9.7 Anomalous origin of one coronary artery from an inappropriate sinus and with an inter-arterial proximal epicardial course. A plasticine model of the three commonest occurrences of such a situation.


In this group the most common anomaly is origin of the left coronary artery from the right sinus of Valsalva (Figure 9.8). Origin of the right artery from the left sinus is less frequent (Figure 9.9). It is proposed as a cause of sudden death usually on exertion. In a proportion of cases the artery has an intramural course in the aortic wall before exiting onto the adventitial surface. Frequently there is fibrosis in the myocardium of the affected supplied part of myocardium.






(A) The left ventricular outflow tract of the heart opened to demonstrate anomalous origin and intramural course of the left coronary artery from the right sinus of Valsalva. The right coronary artery can be seen at the centre of the field arising from the right-facing sinus of the aortic valve. Immediately to its left is an elliptical depression where the left coronary artery takes origin, running through the aortic wall to exit on the epicardial surface adjacent to the usual position of the left coronary artery. No coronary artery orifice is seen in the left sinus.





(B) The aorta viewed from behind. The origins of the coronaries can be discerned in the opened aorta. To the left the emergence of the left artery from the aortic wall is visible.





(C) A histological section demonstrates the intimate relation of the proximal course of the left coronary artery and the aortic wall. The pulmonary trunk is to the left and the coronary artery runs between the two great vessels.



Figure 9.8 Origin of the left main stem from the right sinus of Valsalva.






(A) The left ventricular outflow tract is opened to show the aortic valve. The left coronary artery orifice is the larger and arises from the centre of the left sinus of Valsalva. The right artery orifice is smaller and arises from the left sinus close to the commissure.





(B) The epicardial aspect of the same case showing the oblique origin of the right coronary artery and its proximal course between the aorta and the pulmonary trunk


(From Suvarna SK (ed.) Cardiac Pathology: A Guide to Current Practice. London: Springer; 2013, with permission).


Figure 9.9 Origin of the right coronary artery from the left sinus of Valsalva.


An abnormally high take-off of the coronary arteries from the aorta, arbitrarily defined as greater than 1 cm above the sinotubular junction, may be associated with increased cardiac morbidity, possibly because of an oblique course through the aortic wall [19,20].


The situation of disconnection of the coronary arteries from their aortic attachment has already been mentioned in the context of pulmonary atresia with intact ventricular septum [21].



9.5 Coronary Artery Fistula


Congenital coronary fistula is rare [22]. The fistulous communication is between one or both coronary arteries and the coronary sinus, the pulmonary trunk or one of the cardiac chambers. Coronary fistula may occur in isolation, or may be associated with other cardiac abnormalities such as pulmonary atresia with VSD (Figure 4.41A) or hypoplastic left heart [23]. The defect results in left-to-right shunt and, depending on the magnitude of the shunt, symptoms develop. This usually does not occur until adulthood when the patient may develop congestive cardiac failure or bacterial endocarditis [24]. Only 10–20% of childhood cases are symptomatic [25]. Rupture is a very rare occurrence [26]. Intervention in childhood is rarely needed [27].


The affected vessel is more frequently the right coronary artery. The vessels are enlarged and thin-walled and tortuous (Figure 9.10); further aneurysmal dilatations may be present with fibrosis and calcification of their walls. The changes become more noticeable with age. When there is fistula between the coronary artery and coronary sinus, the coronary sinus is also dilated and tortuous. Histologically the walls of the affected but non-aneurysmal artery show medial hypertrophy with disruption of its elastic laminae, and intimal fibrosis (Figure 4.41B). The aneurysmal parts show fibrous replacement of the wall with focal calcification [27]. The treatment of choice is transcatheter closure [28].





Figure 9.10 Coronary artery fistula. Fistula between the right coronary artery and the coronary sinus. The course of the right coronary artery in the right atrioventricular groove is opened from its aortic origin. The vessel is greatly dilated and tortuous and has a roughened intimal surface.


Anomalous connections of the coronary arteries to the pulmonary trunk are dependent on an accessory coronary artery arising from the pulmonary trunk. Coronary artery fistula may be acquired, particularly in association with Kawasaki disease [29].



9.6 Coronary Artery Hypoplasia and Atresia


Both coronary artery hypoplasia and atresia are rare and are usually associated with other cardiac defects. Pulmonary atresia with intact septum and ventriculocoronary sinusoids may be associated with coronary atresia. Isolated hypoplasia has been reported as a cause of sudden death [30].



9.7 Variations in the Epicardial Coronary Arteries in Congenital Heart Disease


The frequency of abnormal epicardial coronary artery distribution in congenital heart disease with normal outflow tracts appears to be no higher than in normal hearts [31]. Those with conotruncal abnormalities have the highest rate of abnormal coronary distribution.



9.7.1 Tetralogy of Fallot


The commonest abnormality described in tetralogy of Fallot is the origin of the LAD artery from the right sinus of Valsalva or as a branch of the right coronary artery (Figure 9.11). This abnormality accounts for about 80% of abnormal coronary artery patterns [32]. A dominant left coronary artery is found more frequently in tetralogy of Fallot patients compared to normal subjects (28% vs 10%) [33]. In all cases of tetralogy of Fallot the conal branch arising from the right coronary artery is enlarged to supply the hypertrophied right ventricle (Figure 9.12). In some cases it may arise via a separate ostium in the right sinus [32]. The incidence of major coronary artery crossing the right ventricular outflow tract is between 5% [34] and 19% [33], the discrepancy being accounted for, to some extent, by the investigation method (echocardiography vs angiography). There may be fistulae between the left circumflex artery and the bronchial arteries [35].





Figure 9.11 LAD from RCA in tetralogy of Fallot. A one-day-old infant with tetralogy of Fallot. There is a single coronary artery arising from the right sinus of Valsalva.





Figure 9.12 Large conal branch tetralogy of Fallot. The epicardial surface of the heart exposing the right coronary artery. The artery gives rise to several infundibular branches immediately after exiting from the aorta and then turns sharply to the left in the right atrioventricular groove. The LAD artery is visible emerging to the left of the pulmonary trunk.



9.7.2 Transposition of the Great Arteries


Variations in coronary artery anatomy in transposition of the great arteries are more prevalent when the great arteries have a side-by-side arrangement than when the aorta is anterior [36]. The commonest pattern found is the origin of the left artery from the left sinus of Valsalva but with a course anterior to the pulmonary trunk (Figure 9.13). The right coronary artery arises from the posterior sinus [32]. The circumflex artery may also arise from the posterior sinus. There is a six-fold increase in early mortality after arterial switch operation associated with the presence of an intramural coronary artery and a three-fold increase in mortality associated with a single coronary artery [37].






(A) The aorta lies beside the pulmonary artery. The right coronary artery is exposed. In addition to the usual right coronary artery anatomy, the LAD artery arises from the vessel.





(B) The circumflex artery arises normally from the left sinus.



Figure 9.13 Transposition of the great arteries.



9.7.3 Common Arterial Trunk


In common arterial trunk the coronary artery pattern is very variable and depends on whether the arterial valve consists of three, fewer or more leaflets. It is most likely to be normal if the truncal valve is tricuspid (Figure 9.14) [38].





Figure 9.14 Common arterial trunk. The trunk is opened and the VSD is visible as is the orifice of the pulmonary arteries. The origins of the coronary arteries can just be discerned beneath the sinotubular junction.



9.7.4 Double Outlet Right Ventricle (DORV)


The distribution of the coronary arteries in DORV follows the position of the great arteries. The normal pattern is the most frequently observed occurring in about one-third of cases. This is usually the case when the aorta is relatively posterior and rightward and the physiology is similar to tetralogy of Fallot. When the aorta is more anterior, then the coronary artery pattern is similar to the usual pattern seen in TGA (25%). As in transposition, variant coronary artery patterns are often seen in side-by-side great arteries (27%) (Figure 9.15). When the aorta is anterior and leftward, the right coronary artery crosses in front of the right ventricular outflow (Figure 9.16) [39].





Figure 9.15 Double outlet right ventricle. Eleven-year-old with surgically treated DORV. The aortic root is viewed from above. Both coronary arteries arise from the right sinus of Valsalva. They arise very close together, such that from the outside they appear to be a single vessel. But two separate orifices are discernible on the inside. The left artery supplies a branch to the pulmonary infundibulum and the anterior interventricular artery. The right artery supplies the marginal branches on the right side and the posterior interventricular artery and runs behind the left atrium to supply the greater part of the posterior and inferolateral left ventricle.





Figure 9.16 Double outlet right ventricle with anterior and left aorta. The coronary arteries arise from a single sinus of the aortic valve. This sinus is the most anteriorly situated. Two arteries arise each approximately 0.15 cm in diameter. The left artery has a rather oblique angle of origin and supplies the anterior interventricular artery. The posterior interventricular artery is supplied by the right coronary artery. A Blalock–Taussig shunt is visible.



9.7.5 Hypoplastic Left Heart


Left dominance is more frequent in hypoplastic left heart syndrome than in normal hearts, and even more prevalent in the subgroup with mitral stenosis (Figure 9.17) [40]. Ventriculocoronary communications may be present. Most are small and probably have no effect on coronary perfusion (Figure 9.18) [41].





Figure 9.17 Hypoplastic left heart. Explanted heart from a child with mitral and aortic hypoplasia and hypoplastic left ventricle who underwent Norwood operation and subsequently proceeded to heart transplant. The heart is viewed from the base. The Damus–Kaye anastomosis is clearly visible linking the anterior pulmonary trunk and the small aorta. There are two coronary arteries. The right coronary artery is dominant supplying the posterior aspect of the heart. No circumflex artery arises from the left coronary artery.





Figure 9.18 Hypoplastic left heart. Histological section of the left ventricle in an explanted heart with hypoplastic left heart. The left atrium is to the top right of the field, and the arcade of the mitral valve separates it from the left ventricle. The ventricle shows marked fibroelastic thickening of its endocardium, and there is some obliteration of the cavity towards the ventricular apex. The atretic aortic valve site is at the top left. On the right of the picture are multiple irregular channels with fibroelastic walls that communicate with the ventricular cavity and represent coronary artery sinusoids.



9.7.6 Congenitally Corrected Transposition


The coronary artery distribution usually follows that of the ventricles [42]. The coronary arteries arise from an anteriorly situated aorta and have an inverted origin with the coronary artery arising from the left-facing sinus supplying the peripheral distribution of the usual right coronary artery. The right sinus gives rise to an artery supplying the anterior interventricular artery and a circumflex artery [43]. The artery to the sinoatrial node and also that to the AV node arise from the right-sided circumflex artery [44].

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