Origin of the Right or Left Pulmonary Artery from the Ascending Aorta

Definition

Anomalous origin of a pulmonary artery from the ascending aorta is a condition in which the right pulmonary artery (RPA) or rarely, the left pulmonary artery (LPA), arises from the ascending aorta in the presence of separate aortic and pulmonary valves and without interposition of ductal tissue. This condition is sometimes referred to as hemitruncus . Hemitruncus is also used to describe a subset of truncus arteriosus (see Chapter 43 ). Rarely, both right and left pulmonary arteries arise from the ascending aorta in the presence of two separate semilunar valves.

Origins of one or both pulmonary arteries from the transverse aortic arch via a ductus arteriosus or collateral arteries and from the descending thoracic aorta via collateral arteries are not discussed; these conditions are most commonly part of tetralogy of Fallot, but they can occur in the presence of other intracardiac defects or even with normal intracardiac morphology (see Chapter 38 ). When both the RPA and LPA or only one pulmonary artery arise from the ascending aorta with a common semilunar valve, the condition is a subset of truncus arteriosus (see Chapter 43 ).

Historical Note

The first description of this entity was by Fraentzel, who in 1868 reported the case of a 25-year-old woman dying in heart failure, with the RPA arising from the ascending aorta and an aortopulmonary window. In 1914, Doering reported aortic origin of the RPA in an infant dying at age 8 months whose only associated anomaly was a patent ductus arteriosus. Bopp, in 1949, gave a detailed report of this condition ; since then, and with development of cardiac catheterization and angiography, other cases have been reported.

In 1957, Caro and colleagues corrected the malformation by disconnecting the RPA from the ascending aorta and connecting it with an interposition graft to the pulmonary trunk. The patient, a 23-year-old man, died a short time after operation. The first successful repair, which was in a 12-month-old infant, was reported in 1961 by Armer and colleagues. They interposed a graft between the pulmonary trunk and distal end of the divided RPA and closed a coexisting patent ductus arteriosus. In 1967, Kirkpatrick and colleagues reported the first successful cases of retroaortic direct anastomosis of the divided RPA to the pulmonary trunk. The first report of successful surgical treatment of aortic origin of the LPA, in a 6-week-old infant, was by Herbert and colleagues in 1973.

Morphogenesis and Morphology

Morphology

Anomalous Origin of Right Pulmonary Artery

The RPA usually arises from the right or posterior aspect of the ascending aorta ( Fig. 45-1 ) in this condition, but occasionally it arises from the leftward posterior aspect. Its origin is usually within 1 to 3 cm of the aortic valve. Uncommonly, it arises from the distal portion of the ascending aorta just proximal to the origin of the brachiocephalic artery. The RPA origin is rarely stenosed, and the vessel is usually as large as or larger than the normally connected LPA; it is normal in structure, course, and distribution.

When the RPA arises anomalously from the ascending aorta and no other anomalies are present, pulmonary vascular beds of the two lungs may be similar despite differences in origin of the pulmonary arteries. Occasionally, pulmonary and tricuspid valves are dilated as a result of right heart failure, and the tricuspid leaflets may be thickened and edges rolled. Origin of the RPA from the ascending aorta is an isolated lesion in about 20% of cases. In the remainder, the most common coexisting lesion is patent ductus arteriosus, present in about 50% of cases.

Other less common associations are with tetralogy of Fallot, ventricular septal defect, aortopulmonary window, coarctation of the aorta, interrupted aortic arch, and atrial septal defect. Severe contralateral (left) pulmonary vein stenosis may coexist. The vein stenoses are typically tubular, with dilatation of the left pulmonary veins proximal to the stenoses. Also, Sievers and colleagues report coexisting subtotal obstruction of the left pulmonary vein orifices by a membrane that was excised at operation.

Anomalous Origin of Left Pulmonary Artery

Origin of the LPA from the ascending aorta is rare. It occurs as an isolated lesion in about 40% of cases, usually coexisting with right aortic arch. In contrast to origin of the RPA from the ascending aorta, the most common associated anomaly is tetralogy of Fallot. Then, the aortic arch may be left sided. Tetralogy of Fallot with absent pulmonary valve syndrome is also observed ( Fig. 45-2 ).

Anomalous Origin of Both Pulmonary Arteries

Origin of both RPA and LPA from the ascending aorta has been reported in one patient who had no other cardiac anomaly. The origin was by way of a short single trunk coming off the posterior aspect of the ascending aorta, with the pulmonary trunk arising normally from the right ventricle and connected only to a patent ductus arteriosus. Repair was attempted unsuccessfully at age 11 days.

Clinical Features and Diagnostic Criteria

When the condition is isolated except for a patent ductus arteriosus, the patient characteristically presents early in infancy with respiratory distress and heart failure. Frequently the infant is acutely ill. There may be cyanosis from (1) venous admixture in the lungs or (2) reversed shunting through a patent ductus arteriosus or a patent foramen ovale resulting from right heart failure.

There are no typical auscultatory findings, and murmurs may or may not be present. When present, the murmur is usually systolic and heard along the left sternal border. Rarely, it may be continuous as a result of kinking or stenosis of the artery. The peripheral pulses are jerky or bounding because of rapid runoff from the aorta into the lung and consequent left-to-right shunting. Electrocardiographic findings are not diagnostic and usually indicate biventricular and right atrial enlargement. Cardiomegaly is usually severe on the chest radiograph, with the heart assuming a globular shape. Pulmonary plethora is usually of similar degree bilaterally.

When tetralogy of Fallot is present with severe pulmonary stenosis, clinical features are dominated by the tetralogy. The condition may be suspected, however, because the lung supplied by the anomalously arising artery is usually plethoric, whereas the other lung is oligemic. Since the early 1990s, correct diagnosis and assessment have been adequately made with two-dimensional echocardiography alone, making cardiac catheterization unnecessary ( Fig. 45-3 ). However, cardiac catheterization and cineangiography provide additional information. Pressure in the pulmonary artery arising from the aorta is systemic in almost all cases, because ostial stenosis is rare. As already noted, pressure in the pulmonary artery that arises normally is usually also elevated to systemic or suprasystemic levels. Accurate measurement of pulmonary and systemic blood flows is difficult in this situation but not critical, because the infants usually present with clear clinical evidence of increased pulmonary blood flow. Pulmonary vascular resistance in the normally connected lung can be calculated and is a useful guide to operability—and an essential guide in older patients.

Cineangiography is diagnostic, and a right ventriculogram or pulmonary angiogram opacifies only the normally connected pulmonary arteries. Antegrade or retrograde aortography shows the pulmonary artery that arises from the ascending aorta ( Fig. 45-4 ). Cineangiography is also used to define other cardiac anomalies that may be present.

In neonates and infants in whom catheterization is not critical, computed tomography angiography can confirm morphologic details suspected by echocardiography ( Fig. 45-5 ).

Natural History

Anomalous origin of a branch pulmonary artery from the ascending aorta is rare, reportedly accounting for 0.12% of all congenital heart defects. Nearly all cases involve the RPA. As of 2004, 136 cases of RPA from the aorta had been reported, and from 2004 to 2010, at least 35 additional cases appeared in the literature. In 2003, Prifti and colleagues reviewed the reported experience with LPA from the aorta and found 77 cases; however, many of these appear to have had LPA origins from the descending thoracic aorta or from a ductus, with a high association with tetralogy of Fallot, and thus likely represent a different lesion. It is a lethal condition. About 70% of surgically untreated patients are dead by age 6 months and 80% by age 1 year ( Fig. 45-6 ). Intractable heart failure is the usual mode of death.

Pulmonary hypertension in the anomalous pulmonary artery is uniformly present, and commonly it is also present in the normally connected pulmonary artery. This finding is supported by Pool and colleagues’ observation that pulmonary hypertension develops in 19% of infants born with unilateral absence of a pulmonary artery and no associated malformations, and that ligation of one pulmonary artery within 24 hours of birth in five calves resulted in severe pulmonary hypertension in the opposite lung within 2 months. Surprisingly, Keane and colleagues report no important obstructive vascular changes in either lung in most patients dying in the first 6 months of life. This does not mean that pulmonary hypertension was not present, just that pathologic changes were not evident.

Among older patients, pathologic evidence of hypertensive pulmonary vascular disease is usually present, often to a similar extent in the two lungs, sometimes greater in the right and sometimes greater in the left. It is likely that the natural history of isolated origin of the LPA from the ascending aorta is similar, but too few patients have been observed to establish this.

Technique Of Operation

Preparations for operation, median sternotomy, and cardiopulmonary bypass (CPB) are those normally used (see “Preparation for Cardiopulmonary Bypass” in Section III of Chapter 2 ), as are the techniques for myocardial management (see “Cold Cardioplegia, Controlled Aortic Root Reperfusion, and [When Needed] Warm Cardioplegic Induction” in Chapter 3 ). The technique is described for anomalously arising RPA; it is similar when the LPA is affected.

Once the pericardium has been opened, the anomalously originating RPA is visualized coming from either the posterior or right lateral aspect of the ascending aorta ( Fig. 45-7, A ). It passes into the right hemithorax behind the superior vena cava. The aorta is completely dissected from the pulmonary trunk, and the ductus arteriosus is dissected out at this point.

The purse-string sutures and preparation for CPB are made as usual, except that care is taken to place the aortic cannula far enough downstream so that the aorta may be occluded distal to the aortic origin of the RPA (see Fig. 45-7, A ). A single venous cannula is placed into the right atrium. CPB is established as usual, and as soon as it has begun, a temporary arterial clamp is placed across the RPA.

The ligamentum arteriosum or ductus arteriosum is ligated and specifically divided. Division allows improved mobility of the pulmonary trunk so that the connection to the RPA can be performed with minimal tension. A vent catheter is placed in the left atrium through a purse-string in the right upper pulmonary vein. After the aorta is occluded well distal to the RPA, cold cardioplegia is administered. The clamp is removed from the RPA, which is then thoroughly mobilized beneath the superior vena cava out to the lobar branches.

The pulmonary artery is then disconnected from the ascending aorta (see Fig. 45-7, A ). The defect left in the ascending aorta is closed by a pericardial patch or other patch material ( Fig. 45-7, B ). In some cases, it may be possible to close the aorta transversely by direct suture. The aorta is rotated anteriorly and leftward. The right side of the pulmonary trunk is pulled out from beneath the aorta (see Fig. 45-7, B ), and a longitudinal incision is made in it. An anastomosis is made between the end of the well-mobilized RPA and the side of the pulmonary trunk ( Fig. 45-7, C ). A 7-0 polypropylene suture is used, sewing from within the vessels posteriorly and working external to the vessels anteriorly. The completed repair establishes continuity between the RPA and pulmonary trunk, eliminating the shunt ( Fig. 45-7 , inset ).

An alternative technique that achieves greater length on the RPA was described by van Son and Hanley ( Fig. 45-8, A ). After the aorta is occluded, it is incised transversely at the level of RPA origin. The aortic incision is continued posteriorly, leaving a generous cuff of posterior wall around the origin of the RPA. Position of the left coronary artery is noted and its ostium protected from injury. An incision is made in the right lateral wall of the pulmonary trunk so as to create an anteriorly based flap ( Fig. 45-8, B ). An anastomosis of the RPA to the pulmonary trunk is created with the two flaps forming the proximal segment of the RPA ( Fig. 45-8, C ). The ascending aorta is reconstructed by end-to-end anastomosis ( Fig. 45-8, D ).

The operation is completed in the usual fashion. It is advisable not only to place left and right atrial pressure catheters but also to insert an additional catheter into the right atrium and advance it across the tricuspid valve for monitoring pulmonary artery pressure during the first 48 or more postoperative hours.