Closure of the patent ductus arteriosus by Gross in 1938 marked the beginning of modern cardiac surgery. Although the patent ductus is frequently associated with other cardiac anomalies, this chapter will concentrate on the infant in whom this is an isolated problem.

In a full-term infant, the ductus arteriosus connects the main pulmonary trunk with the descending aorta about 5 to 10 mm distal to the origin of the subclavian artery. It is 5 to 10 mm in length and has an average diameter of 10 mm. The aortic orifice is wider than the pulmonary orifice, although wide variations in size are possible. The recurrent branch of the left vagus nerve loops around the lateral and inferior aspect of the ductus.

The ductus arteriosus is crucial for the fetal circulation, permitting flow from the right ventricle (and hence the placental circulation) to the systemic bed, bypassing the high resistance prenatal pulmonary circulation. The ductus thus carries 55 to 60 per cent of the combined ventricular output.

Postnatal closure of the ductus occurs in two stages. Some 10 to 15 h after birth (in full-term infants) contraction of the medial smooth muscle leads to shortening of the duct and protrusion of intimal cushions into the lumen, resulting in a functional closure. Some 2 to 3 weeks after birth, infolding of the endothelium with necrosis and proliferation of subintimal layers leads to fibrosis and permanent sealing of the lumen. Closure begins at the pulmonary end of the duct; it may remain incomplete at the aortic end.

Ductal closure is mediated by the interaction of oxygen tension and prostaglandins. Prostaglandins, especially prostaglandin E&sub2;, keep the ductus open, while high oxygen tension after birth leads to duct closure. Response to prostaglandin and oxygen varies with duct maturity: in the full-term infant the duct is sensitive to oxygen, while in the premature infant prostaglandins have a dominant effect. Consequently, in premature infants failure of ductal closure results from incomplete ductal development, whereas in full-term infants, a patent ductus arteriosus results from structural abnormalities of ductal tissue. Under physiological conditions other factors such as vasoactive substances (such as acetylcholine, bradykinin, and endogenous catecholamines, or variations in pH) may contribute to ductus closure.

The ductus arteriosus is completely closed by 8 weeks of age in 88 per cent of infants with an otherwise normal cardiovascular system. The incidence of isolated patent ductus arteriosus in term infants is about 1 in 2000 live births; it accounts for 5 to 10 per cent of all types of congenital heart disease.

Clinical symptoms are related to the shunt flow between aorta and pulmonary artery, which is determined by the size of the ductus, systemic and pulmonary vascular resistance, and pressure.

In neonates with a large patent ductus arteriosus, aortic and pulmonary artery pressure are practically equal. As neonatal pulmonary vascular resistance decreases after birth, left to right shunting rapidly increases, and severe left ventricular failure with pulmonary oedema may occur early in infancy.

Physical examination shows a hyperdynamic precordium, occasionally with a palpable systolic thrill and cardiac enlargement. The pulse is bounding and the pulse pressure is wide. The first and second heart sounds are accentuated; a murmur is present, which is more systolic than ‘machinery’ in its characteristics. Occasionally a mid-diastolic mitral flow rumble can be heard at the apex.

Many patients with moderate patent ductus arteriosus remain asymptomatic until the second decade of life, when easy fatiguability and exertional dyspnoea occur. Findings on physical examination are less marked than those in patients with a large patent ductus arteriosus. The classical continuous murmur, which masks the heart sounds and is described as ‘machinery’ in its quality, leads to the diagnosis.

Most patients with a small patent ductus arteriosus are asymptomatic, a systolic murmur in the second left interspace being the only detectable abnormality.

Clinical symptoms improve in infants with a significant, uncorrected left to right shunt as pulmonary vascular resistance increases. Once pulmonary vascular resistance exceeds the systemic vascular resistance, cyanosis develops, and the condition may then be irreversible. Generally, these changes begin by the age of 2 years; they may take several years to develop.

Left ventricular hypertrophy and left ventricular enlargement with left atrial hypertrophy are present in patients with a significant shunt, but may be absent if the shunt is small. Right ventricular hypertrophy occurs with the appearance of increased pulmonary hypertension.

The chest radiograph may be normal in patients with a small patent ductus arteriosus. Enlargement of the heart with pulmonary overperfusion with or without pulmonary oedema and a prominent ascending aorta are typical findings of in patients with a moderate or large patent ductus arteriosus.

In infants and young children with typical, uncomplicated patent ductus arteriosus, cardiac catheterization is not necessary for diagnosis and surgical ligation. Two-dimensional echocardiography with Doppler flow imaging allows direct imaging of the ductus, confirmation of ductal flow, and assessment of shunt magnitude.

If catheterization is performed, an increase of pulmonary arterial blood oxygen content of more than 0.5 ml/dl or a saturation increase of more than 4 to 5 per cent over that of right ventricular blood indicates a significant left to right shunt. If the anatomical situation is unclear, angiocardiography or magnetic resonance imaging can provide additional information (Fig. 1) 1683.

Congestive heart failure, pulmonary hypertension with vascular damage, infective endarteritis, and aneurysmal dilatation of the ductus complicate the clinical course.

Once the diagnosis is made, surgical closure of the duct is indicated. Elective operation should be performed in asymptomatic children before the age of 2 years. Surgical closure within the first 6 months of birth is indicated only in symptomatic patients, since spontaneous duct closure may still occur.

Medical management in this group focuses on treatment of cardiac failure; indomethacin treatment is not effective for producing duct closure. Occlusion of the patent ductus arteriosus can be achieved by transfemoral catheterization in selected cases.

Pulmonary hypertension is not a contraindication to surgery, as long as the shunt flow is predominantly left to right and is not reversed because of severe pulmonary vascular disease.

All neonates with a birth weight of 1000 g or less have a patent ductus arteriosus; this is haemodynamically significant in 40 per cent of these infants. A symptomatic or significant patent ductus arteriosus is strongly correlated with respiratory distress, necrotizing enterocolitis, and cardiac failure. Increased oxygenation, diuretic therapy, and indomethacin (0.2 mg/kg IV) can induce ductal closure in most neonates. Up to three doses of indomethacin can be given safely at an interval of every 12 to 24 h provided renal function is monitored closely. Contraindications to indomethacin therapy include bleeding disorders, impaired renal function, and necrotizing enterocolitis.

The chest is entered through a posterolateral thoracotomy in the fourth interspace and the mediastinal pleura is opened over the upper descending aorta (Fig. 2) 1684. The ductus is freed from attachments to the mediastinal tissue, and a heavy ligature is passed around the ductus to facilitate further dissection. The recurrent laryngeal nerve should not be dissected free. The ductus can be interrupted by division or by ligation: both produce excellent results.

In preterm infants interruption of the ductus with a medium-sized stainless steel or titanium haemostatic clip (Hemoclip®, Weck & Co) is the preferred technique. In infants and children under 1 year of age the ductus is usually ligated with one strand of No. 1 braided polyester ligature (Tevdek®, Deknatel Inc.) on the aortic side and a haemostatic clip on the pulmonary artery side (Fig. 3) 1685. In older children, or in those with a large ductus, the ductus should be divided, the aortic and pulmonary ends being oversewn with continuous 5–0 polypropylene (Prolene®, Ethicon Inc.) suture (Fig. 4) 1686. Closure of patent ductus arteriosus in adults, especially when the aortic end is calcified, may require cardiopulmonary bypass and closure through the open pulmonary artery.

Postoperative care of patients with repair of an uncomplicated patent ductus arteriosus should be uneventful. The chest tube is removed in the operating room or a few hours after surgery.

The operation is one of the safest in cardiac surgery. Hospital mortality is almost zero in patients with an uncomplicated patent ductus arteriosus. Cardiac failure, pulmonary hypertension, and advanced age increase the operative risk; closure of an uncomplicated patent ductus arteriosus in infancy or childhood provides a normal life expectancy. These results support closure of a patent ductus arteriosus even in asymptomatic patients, when compared to the risks and complications of leaving the condition.

Coarctation of the thoracic aorta affects 5 to 8 per cent of infants with congenital heart disease, with a male/female ratio of 2:1 for isolated coarctation. The lesion varies considerably in severity of constriction, as well as in its length and location.

Two major types of coarctation can be identified, depending on the blood supply of the lower body.

A localized thin membrane of infolded aortic media and intimal hyperplasia is usually found in a juxtaductal or postductal position, and is considered to be derived from ductal tissue. Blood flow to the lower body is supplied by the left ventricle through the ascending aorta and most patients survive to adult life. Other cardiac anomalies are rare.

A local membrane is associated with a diffuse narrowing of the aortic isthmus, called tubular hypoplasia. Blood supply to the lower body may be provided by the right heart through a patent ductus arteriosus; patients generally become symptomatic during infancy. This lesion is often associated with other cardiac abnormalities, such as patent ductus arteriosus, ventricular septal defects and aortic and mitral stenosis.

The exact cause of coarctation remains controversial: ectopic ductal tissue or changes in the fetal flow pattern in the ductus and ascending aorta have been suggested.

Collateral arterial circulation from branches of the subclavian, internal mammary, intercostal, and scapular arteries is variable. It is well developed in adults, but is unusual in infants.

Infants with coarctation generally present with congestive heart failure and signs of systemic hypoperfusion, possibly including metabolic acidosis. Physical examination shows a hyperdynamic precordial impulse and a non-specific pansystolic murmur along the left upper sternal border. Murmur characteristics may change with different associated cardiac anomalies. In patients with normal cardiac output, hypertension can usually be detected in the upper limbs. A systolic pressure difference between upper and lower extremities of more than 20 mmHg is present, but may be absent if cardiac failure is severe, when reduced aortic blood flow yields a smaller gradient across the coarctation.

Older children and adults are generally asymptomatic. The first finding is either a murmur or hypertension. Physical examination shows decreased or absent femoral pulses. In less severe cases or when collateral vessels provide enough distal blood flow, peripheral pulses may be relatively equal. Blood pressure measurements in upper and lower extremities are necessary to detect the gradient.

A pressure difference between both arms suggests that the origin of one of the subclavian arteries, in most cases the left, is below the coarctation.

Infants with symptomatic coarctation may show right axis deviation and signs of right ventricular hypertrophy. In older children and adults left ventricular hypertrophy is the dominant sign.

The symptomatic infant generally shows cardiac enlargement with pulmonary overperfusion. In older patients, the chest radiograph reveals a prominent left ventricle with the cardiac silhouette at the upper limit of normal. After 8 to 10 years of age, characteristic rib notching occurs, caused by markedly enlarged intercostal arteries.

Echocardiography can establish the diagnosis and assess associated cardiac anomalies, especially in the critically ill infant. After stabilization of these patients, cardiac catheterization and angiography will provide valuable preoperative information, such as delineation of anatomy and measurement of the isthmus size. This allows precise planning of the operation. In the older patient, additional information about the coronary artery status and the collateral circulation can be obtained. Magnetic resonance imaging can demonstrate the precise anatomy of the lesion (Fig. 5) 1687.

Life expectancy in patients with isolated coarctation is about half of that of the normal population: death is mainly due to heart failure, rupture of the aorta, and cerebral haemorrhage.

Treatment of coarctation is surgical, performed between 4 and 6 years of age, or earlier in patients with severe hypertension or cardiac failure. Delay of surgery increases the risk of persistent postoperative hypertension, whereas operation before 1 year of age bears an increased risk of recurrent coarctation.

Some neonates with coarctation develop severe left heart failure when the ductus arteriosus starts to close. These patients require immediate treatment with prostaglandin E&sub1; infusion to keep the ductus open, to reduce left ventricular failure, and to improve perfusion of the lower body. The initial dose is 0.1 &mgr;g/kg.min; this can be reduced in small increments to a minimum dose of 0.05 &mgr;g/kg.min as long as ductal patency is maintained. After stabilization of the medical condition of the infant, surgery should be performed as soon as possible. Lack of an immediate response to prostaglandin treatment is an indication for emergency surgical intervention.

The chest is entered via a left posterolateral thoracotomy in the fourth intercostal space or through the bed of the fifth rib. The mediastinal pleura is incised over the aorta posterior to the vagus nerve, starting about 4 cm below the coarctation and up to the entire proximal portion of the left subclavian artery (Fig. 2) 1684. Staying just superficial to the adventitia, the proximal left subclavian artery with the adjacent parts of the aortic arch and the ligamentum arteriosus are dissected and are isolated with tapes. Dissection of the aorta is continued distal to the coarctation, avoiding injury to the friable intercostal arteries. The ligamentum arteriosus or patent ductus is then ligated and divided.

In young infants, if the coarctation is long or the isthmus hypoplastic, the subclavian flap technique (Fig. 6) 1688 is preferred. The aortic cross-clamp is placed proximally between the left common carotid artery and left subclavian artery, and a second clamp is placed well distal to the coarctation, but preferably proximal to the intercostal arteries. The subclavian artery is ligated, divided, and incised longitudinally. The incision is continued on to the aorta and is carried beyond the coarctation. The local membrane shelf is excised carefully, taking care not to penetrate the posterior aortic wall. The subclavian flap is turned down and sutured continuously along the edges of the incision using 5–0 or 6–0 monofilament absorbable sutures. Alternatively 6–0 or 7–0 interrupted non-absorbable sutures can be used. It is crucial for the success of this technique that the aortotomy extends well beyond the coarctation.

In most other cases, resection of the coarctation with direct end-to-end anastomosis (Fig. 7) 1689 of the aorta is preferred. After sufficient mobilization of the proximal and distal aorta, the proximal aortic clamp is placed at the origin of the left subclavian artery and the distal clamp as described above. The aorta is transected proximal and distal to the coarctation, and the ends are approximated. Anastomosis is then performed with continuous 6–0 or 5–0 polydioxanone suture (PDS®, Ethicon Inc.) in infants and children to allow the anastomosis to grow and with 3–0 polypropylene in adults because it need not grow. Alternatively, an interrupted technique can be used.

If approximation of the divided aortic ends is not possible without tension on the suture line, insertion of a woven Dacron tube graft is used in adults. A minimum graft diameter of 18 mm is required to avoid a residual pressure gradient. Prosthetic patch aortoplasty is currently controversial because of possible aneurysm formation in the aortic wall opposite the prosthetic patch. The aneurysm probably forms because of excessive removal of the coarctation membrane.

In technically difficult situations, especially in reoperations, a Dacron bypass graft can be used in adults to bridge the coarctation, usually without complete cross-clamping of the aorta.

After completion of the anastomoses, the distal clamp is removed, followed by the slow opening of the proximal clamp to prevent a rapid blood pressure drop. The mediastinal pleura is closed, and a single chest tube is inserted for pleural drainage.

Hypertension can be observed in many patients for 2 or 3 days after surgery, sometimes combined with mild abdominal discomfort. If hypertension remains untreated, abdominal tenderness, fever, and leucocytosis can occur; intestinal necrosis due to mesenteric arteritis is occasionally seen. The use of preoperative treatment with propranolol and postoperative treatment with propranolol, labetalol, nitroprusside, and angiotensin converting enzyme inhibitors have made such complications rare.

Another rare but serious complication is paraplegia, which occurs in about 0.4 per cent of patients after operation. Insufficient collateralization, resulting in reduced perfusion of the anterior spinal artery during surgery, appears to be the cause.

Recurrence of coarctation, defined as a resting peak pressure gradient greater than 20 mmHg across the repair area, is a late complication. This may be associated with operations performed in early infancy and the use of end-to-end anastomosis. The subclavian flap angioplasty technique has improved the outcome in young infants, but controversy remains over which is the best technique.

Percutaneous balloon angioplasty can be used with good results in selected patients with recurrent coarctation. It is not recommended as a primary technique in patients who have not undergone previous surgical treatment.

The mortality rate in patients treated for isolated coarctation during the hospital stay, with or without associated patent ductus arteriosus, is approximately 1 per cent, and continues to decrease. Almost all late deaths occur within 1 year of operation. Approximately 90 per cent of patients who undergo a coarctation repair after infancy and leave hospital are still alive after 25 years.

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