In this chapter, we will address the various congenital coronary arterial anomalies that may be found in the otherwise structurally normal heart. The coronary arterial circulations found specifically with major cardiac structural anomalies will be discussed in the respective chapters elsewhere in this textbook. Similarly, those abnormalities of the coronary arteries that are acquired or associated with diseases will be discussed separately in their respective chapters.
INCIDENCE AND PREVALENCE
Anomalies of the coronary arteries are rare, occurring in 0.3% to 1.3% of one autopsy series. 1 The prevalence, however, is extremely difficult to estimate, as this depends upon accurate recognition and specific identification. This task is complicated by the occurrence of coronary arterial anomalies that, in many individuals, do not lead to symptoms, morbidity, or mortality. In fact, precise diagnosis may escape notice both during life and postmortem.
MORPHOLOGY
The normal coronary arterial anatomy was well described by James 2 ( Fig. 45-1 ). Two arterial orifices are placed, usually relatively centrally, in the right and left sinuses of Valsalva. The right coronary artery arises from the right sinus of Valsalva. Having entered the atrioventricular groove, it sends an infundibular branch anteriorly, and then courses backward and inferiorly, terminating in the majority of hearts in the inferior interventricular groove. In approximately 50% of people, there is a separate origin of the infundibular branch. 3 The main stem of the left coronary artery arises from the left sinus of Valsalva, emerging perpendicularly for a few millimetres. It then bifurcates into anterior interventricular and circumflex branches. The former courses in the anterior interventricular groove toward the cardiac apex, while the latter courses around the left atrioventricular groove and, in one-tenth of individuals, gives rise to the inferior interventricular artery, often then continuing to supply the diaphragmatic surface of the right ventricle. In 1% of people, there are separate origins of the circumflex and anterior interventricular arteries from the left sinus. 3
When both right and circumflex coronary arteries supply a branch to the inferior interventricular groove, the system is said to be balanced. More usually, in 90% of individuals, it is the right coronary artery that supplies one large or two smaller branches to this groove, with no contribution from the circumflex artery. This is called right coronary arterial dominance. In the left dominant system, as already described, the converse is true. All three variations of coronary arterial supply to the inferior interventricular groove and the diaphragmatic surface of the hearts are considered to be normal ( Fig. 45-2 ).
The left and right coronary arteries provide branches superiorly to the atriums, and inferiorly to the ventricles. The major branches remain superficial, and are visible through the epicardium until they terminate in broom-like arborisations that penetrate the myocardium. Over the left ventricle, these penetrating arteries proceed perpendicularly through the wall, being occluded by ventricular contraction. In consequence, the left ventricular myocardium is perfused predominately during diastole.
MORPHOGENESIS
The normal development of the coronary arteries is well proven, and provides the context in which the various anomalies and abnormalities can be understood. When myocardial cells are first observed to contract, there is no defined coronary circulation. The cells are loosely assembled, being bathed in the blood which they pump. The walls of the heart condense in gradual fashion, initially with persistence of an extensive trabeculated luminal meshwork. Early studies 4 had suggested that the coronary arteries themselves appeared as buds from the developing roots of both the aorta and the pulmonary trunk. It was subsequently shown that the coronary arteries originate specifically from the sinuses adjacent to the pulmonary trunk, which have a particular spatial configuration such that there is a positive transverse and a negative longitudinal curvature. 5 This has an effect on the wall tension whereby it is increased, perhaps acting as a stimulus for coronary bud development. The distal coronary arteries develop from a network of capillaries originating in the epicardium, with this system then sending major branches into the aortic sinuses. 6
The numerous anomalies of the coronary arteries can then be well explained on the basis of abnormal patterns of morphogenesis. For example, there can be rudimentary persistence of an embryological coronary arterial structure, failure of normal coronary arterial development, failure of the normal atrophic process of development, or misplacement of connection of an otherwise normal coronary artery. 7 As a result, anomalies include abnormal origin, abnormal course, abnormal number, abnormal orifices, and abnormal connections or communications. It is these variations, along with their associated pathophysiology, diagnosis and management, which we discuss in the paragraphs which follow.
ORIGIN OF THE LEFT CORONARY ARTERY FROM THE PULMONARY TRUNK
Incidence
Origin of the left coronary artery from the pulmonary trunk ( Fig. 45-3 ) is one of the more common coronary arterial abnormalities encountered in children. Also referred to as anomalous left coronary artery from the pulmonary artery, this variation occurs in from 1 in 250 to 1 in 400 of all congenitally malformed hearts, with an overall incidence of approximately 1 in 300,000 children. 8 This anomaly is seen with greater frequency in boys than it is in girls, with the ratio being 2.3 to 1. 9
Pathophysiology
In the fetus with the origin of the left coronary artery from the pulmonary trunk, the myocardium, valves, and vessels otherwise develop quite normally. The perfusion pressure for the coronary arteries is the arterial pressure in the arterial trunk supplying these vessels minus the pressure of the chamber receiving the coronary venous flow. As the myocardium is contracting during systole, most flow occurs during diastole. Thus, in the normal situation, the coronary perfusion pressure is the aortic diastolic pressure minus the pressure in the right atrium. During fetal development, the diastolic pressure is nearly identical in the pulmonary arteries and the aorta. Thus, the coronary arterial perfusion in the fetus with the origin of the left coronary artery from the pulmonary trunk is virtually the same as in the normal fetus.
After birth, as long as the pulmonary arterial pressure remains at or near systemic levels, the left ventricular myocardium supplied by the anomalous artery remains well perfused. As the pulmonary vascular resistance, and subsequently the pressure, in the pulmonary trunk falls postnatally, the perfusion of the left ventricle becomes vulnerable, the period during which pressure in the left coronary artery exceeds intramural left ventricular pressure becoming shorter. This circulatory handicap reduces left ventricular function, and raises left ventricular end-diastolic pressure. In time, there may be a reversal of flow through the left coronary artery should the pressure in the pulmonary arteries fall below that of the left ventricle. This reverse flow leads to the phenomenon referred to as coronary arterial steal, which can lead to further ischaemia of the ventricular myocardium. When the left coronary artery originates from the pulmonary trunk, it is, of course, also perfused with pulmonary blood, which after birth has a much lower content of oxygen than does the blood in the aorta. In some cases, the ischaemic myocardium can be perfused increasingly by a set of developing collateral connections from the right coronary artery, which arises normally ( Fig. 45-4 ). Ideally, a superb set of perfectly distributed collateral arteries could be developed before the pulmonary arterial pressure has fallen sufficiently to result in significant ischaemic damage to the left ventricle. In many circumstances, however, the collateral connections may develop, but be poorly distributed. In consequence, some portions of the left ventricle may be well perfused, while others become ischaemic.
In another pattern of abnormal distribution of the collateral arteries, there are large interconnections proximal to the branches supplying contracting myocardium that act as left-to-right, or aortopulmonary, arterial shunts, requiring extra work from the left ventricle while deviating blood supply from its myocardium. This malformation presents a picture postnatally that may vary enormously from patient to patient, and also from time to time in a given patient. 10 The end result is best evaluated in terms of time of onset of clinically observable myocardial ischaemia. At one extreme, this may never occur, while, at the other, there is disastrous damage to the myocardium in the first weeks of infancy ( Fig. 45-5 ).
Typically, the right coronary artery enlarges at its origin, while the left tends to be small, and relatively thin-walled. The collateral circulation between the right and left systems may be diffusely large, and well distributed. As a result, the left ventricle may remain quite well perfused, allowing the heart to retain its essentially normal form and function. When the collateral connections are poorly developed, the left ventricle becomes ischaemic, dilated, infarcted and fibrosed (see Fig. 45-5 ). Often the fibrosis extends into the papillary muscles and the mitral valve itself. Mitral valvar competence may be compromised by these changes, as well as by dilation caused by ischaemia, resulting in stretching of the annulus. The right ventricle, and parts of the left, which are perfused by the right coronary artery, continue to contract well. The left atrium tends to enlarge, as a result of the increasing left ventricular filling pressure, the mitral regurgitation, or both. This will lead to passive congestion of the lungs, an increase in the pulmonary arterial pressure, and subsequently an increase in the pressures in the right heart.
Presentation
The majority of those with origin of the left coronary artery from the pulmonary trunk present during infancy. The infant with myocardial ischaemia tends to have both the classic signs and symptoms of congestive heart failure. Some affected infants will demonstrate a particular type of anginal attack. Brought on usually by the stress of feeding or defaecation, these are episodes in which the infant suddenly appears to be in severe distress, grunting or crying in short gasps, and is dyspnoeic, grey and sweaty. The child who has escaped myocardial ischaemia in infancy may present rather innocuously on a routine examination with an unexplained heart murmur, mild cardiomegaly or an abnormal electrocardiogram. Myocardial ischaemia may first present in adolescence or young adult life when, under the stress of maximally motivated exertion, either anginal pain or arrhythmia may occur. The latter may produce sudden unexplained death, or so-called near-miss death. The patient also may present with progressive mitral regurgitation, which may or may not be accompanied by electrocardiographic signs of ischaemia. All neonates and infants who present with mitral regurgitation should be evaluated thoroughly for the possibility of origin of the left coronary artery from the pulmonary trunk.
The sick infant may have the general appearance of a baby in chronic congestive heart failure, may have the episodes described above, or may have both. The heart is usually large, and the praecordial impulse is often hyperdynamic. The first heart sound may be loud, normal, or faint, with the second heart sound being loud, and third and fourth heart sounds often present. An apical holosystolic murmur of mitral regurgitation may be heard, and there may be an apical diastolic rumble. The older child with adequate collateral coronary circulation may have completely normal cardiac findings. Sometimes a continuous murmur is heard, resulting from the retrograde flow of blood from the anomalously connected artery into the pulmonary artery. In such patients, the clinical diagnosis may be a small patent arterial duct. In the child with origin of the left coronary artery from the pulmonary trunk, however, there may also be apical murmurs in systole and diastole, resulting from mitral regurgitation and relative mitral stenosis.
Course and Prognosis
It is the extent of collateral vascularisation that dictates the clinical course. Those, likely the minority, with well-developed collateral coronary arteries may have a mild, or even sub-clinical, course with spontaneous improvement. They may present later in childhood, adolescence, or adulthood with progressive mitral regurgitation, congestive heart failure, or myocardial ischaemia with exertion. The overall outlook for the group left untreated, however, is poor. Death may occur suddenly, owing to arrhythmia or to cardiogenic shock from further infarction. In the review of Wesselhoeft and colleagues, 10 almost nine-tenths of the infants with angina and/or failure died. Early and accurate diagnosis to guide surgical treatment, therefore, should be the focus of evaluation.
Management
The treatment is surgical, with several approaches being used over recent years. Surgical treatment has evolved dramatically as the transplantation of small coronary arteries during the arterial switch procedure has become commonplace. The specific aim of therapy is to preserve as much myocardium as possible. 11 The preferred surgical technique in most cases is surgical reimplantation of the left coronary artery into the aorta, thus re-establishing antegrade flow of oxygenated blood. 12 When technical considerations make this operation difficult or impossible, such as when the orifice of the artery is in an unfavourable position, a transpulmonary baffle can be constructed. 13 Bypass grafting using the carotid and internal mammary arteries, or saphenous venous grafts, is now performed much less frequently. The procedure of ligating the left coronary artery has, quite correctly, been abandoned, this decision being supported by long-term studies of outcome. 12 In the small subset of patients in whom the cardiac function is profoundly depressed, transplantation may be a more desirable option. Modern surgical techniques make it possible to support the circulation further by means of devices that assist the left ventricle or provide extracorporeal membrane oxygenation.
ORIGIN OF THE RIGHT CORONARY ARTERY FROM THE PULMONARY TRUNK
This is a far less common anomaly. Though it may occur in isolation, it is associated with other forms of congenital heart disease in up to two-thirds of cases, such as aortopulmonary window, tetralogy of Fallot, or double outlet right ventricle. Like the origin of the left coronary artery from the pulmonary trunk, the anomaly may produce myocardial ischaemia, but often those affected are asymptomatic. 14 Diagnosis is usually made by detailed echocardiography, and may be confirmed by other high-resolution imaging, such as magnetic resonance imaging or computed tomography. The approach to treatment is difficult, since the natural history remains unclear in the asymptomatic patient. In those patients with any evidence of myocardial ischaemia, surgery with re-implantation of the right coronary artery into the aorta is the preferred approach. 15
ANOMALOUS ORIGIN OF A CORONARY ARTERY FROM THE OPPOSITE SINUS OF VALSALVA
Either the right or the left coronary artery can arise from the opposite sinus of Valsalva. Such an anomalous connection may or may not be associated with any symptoms or problems. If the anomalous artery takes an intramural course, or an interarterial course between the pulmonary trunk and the aorta, then significant clinical symptoms may occur. Sudden death may occur, frequently during or soon after competitive sporting events or strenuous exercise. Unfortunately, such sudden death may be the initial presenting event. Although a mechanism for sudden death has not been definitively established, conjecture is that coronary arterial flow is compromised by compression of the coronary artery, so-called interarterial entrapment, restriction at the site of its orifice from the sinus of Valsalva, kinking of the coronary artery itself, or arterial stenosis resulting from the intramural course. 16
Anomalous origin of the left coronary artery from the right aortic sinus carries a higher risk of sudden death than does the anomalous origin of the right coronary artery from the left coronary aortic sinus. 17 The prevalence of the lesion has been estimated at 0.17%. 18 In nine-tenths of cases, there is also an intramural course of the coronary artery. 16 Although the incidence of sudden death in these individuals is unknown, the annual risk of death for the overall population is reported to be 0.24 per 100,000 person-years. 19 Surgical repair is the preferred treatment for symptomatic individuals. 16 There remains, however, considerable discussion as to the best approach to the asymptomatic child known to have this lesion. 7
OTHER ANOMALIES AND VARIATIONS OF ORIGIN AND COURSE OF THE CORONARY ARTERIES
Most anomalies are extremely rare, and may not present in childhood. They may become important in adolescence and early adult life, when extremes of physical exertion may cause significant intolerance of malfunction previously well tolerated. They may also become significant with aging, when the additional effects of atherosclerotic changes typically manifest. These malformations are increasingly recognised, albeit still very rarely, in the investigation of syncopal episodes or near-miss sudden death.
Stenosis or Atresia of the Main Stem of the Left Coronary Artery
This lesion has variable presentation, but may be lethal in infancy. The origin, and sometimes a short length of the artery, either fails to canalise or else involutes after formation ( Fig. 45-6 ). Much as when the left coronary artery arises from the pulmonary trunk, the circulation on the left side depends upon collateral blood flow from the branches of the right coronary artery. The severity of symptoms, signs, and laboratory findings are related inversely to the size and distribution of the collateral vessels. 20 Some of those affected can survive without symptoms for many years. Infants who present with evidence of myocardial ischaemia are urgently in need of correct diagnosis and treatment. Results obtained by angiography during catheterisation in these infants may be confused with those occurring with origin of the left coronary artery from the pulmonary trunk. Typically, aortic angiography will reveal a large right coronary artery that fills the distribution of the left coronary artery via multiple connections from collateral branches. No contrast material will be seen entering the pulmonary trunk. There may be a slight filling of the left coronary artery from the aorta. There will certainly be no filling of the left coronary circuit from the pulmonary trunk on pulmonary arteriography, thereby excluding the origin of the left coronary artery from the pulmonary trunk as the diagnosis. Cross sectional echocardiography will demonstrate the left coronary artery in its normal location, but it will be diminutive or atretic for a few millimetres. Surgical treatment should be undertaken in these symptomatic patients.
