Patent Ductus Arteriosus, Coarctation of the Aorta, and Vascular Rings

Introduction

The prevalence of PDA at several days of age varies from 20% to 80% and varies inversely with gestational age and birth weight. Between 1998 and 2008, the Nationwide Inpatient Sample database demonstrated increase in the prevalence of PDA in the United States from 1.9 to 2.8 per 1000 live births, likely because of increased detection and improvements in prenatal and neonatal care. It is frequently associated with other heart defects ranging in severity from patent foramen ovale to complex congenital malformations. Several genetic defects have been implicated in the development of PDA, including genes that encode prostaglandin receptors and regulators of smooth muscle cell contraction.

Pathophysiology and Natural History

Although the ductus arteriosus shunts mostly right to left in utero, expansion of the lungs shortly after birth results in a decline in the pulmonary vascular resistance and increased pulmonary blood flow and arterial oxygen tension. Ductal closure usually occurs within the first several hours after birth, and is thought to be mediated by loss of the placental source of prostaglandins, increased degradation of prostaglandins within the lungs, and increased arterial oxygen tension, which stimulate constriction of smooth muscle cells within the wall of the ductus. The prostaglandin-mediated mechanism is most active in the ductus of premature infants, whereas oxygen tension primarily promotes ductal closure in the term infant, likely because of differences in cyclooxygenase (COX) isoforms present in the ductal tissue at various stages of gestation. Thus, the PDA of a term infant is generally unresponsive to COX inhibition, whereas the PDA of a premature infant frequently responds.

Spontaneous closure of the ductus within 4 days occurs in 90% to 95% of full-term infants and in 80% to 90% of premature infants at 30 to 37 weeks' gestation. The rate of spontaneous closure is inversely proportional to birthweight, with only 50% spontaneous closure in extremely low-birthweight infants (500-999 g). In premature infants, PDA increases the risk of prolonged ventilation and oxygen requirements, pulmonary hemorrhage, and bronchopulmonary dysplasia. The diastolic steal is associated with renal hypoperfusion, intestinal ischemia, necrotizing enterocolitis (NEC), reduced middle cerebral artery blood flow velocity, and increased risk of intraventricular hemorrhage. The long-term persistence of PDA is associated with development of endocarditis, congestive heart failure, and eventual development of irreversible pulmonary vascular obstructive disease. Estimated mortality without intervention is 60% by 60 years of age.

Clinical Presentation

Presentation ranges from asymptomatic murmur on examination to symptoms of congestive heart failure caused by large left-to-right shunting. Manifestations of pulmonary overcirculation include hypotension, pulmonary edema, and failure to thrive in infants and children. Neonates, particularly premature neonates, may demonstrate intestinal malperfusion and renal insufficiency in addition to respiratory compromise. Cyanosis is occasionally the presenting symptom in older patients with pulmonary hypertension.

Diagnosis

Physical examination reveals the presence of a “to and fro” murmur heard best from the left upper sternal border, and leads to suspicion of PDA. Chest radiography may show cardiomegaly, signs of pulmonary congestion, and pulmonary edema. Transthoracic echocardiography is used to make the diagnosis ( Fig. 113-1 ). Retrograde flow in the descending aorta indicates significant left-to-right shunting. The presence of a left-sided aortic arch must be confirmed if surgical therapy is contemplated, as this influences the choice of incision. Continuous left-to-right shunting through the ductus is expected, and the presence of right-to-left shunting or bidirectional shunting should raise suspicion for pulmonary hypertension. In adults, echocardiographic windows may be suboptimal, and computed tomography (CT) or magnetic resonance angiography may be necessary to establish the diagnosis. Diagnostic cardiac catheterization is only necessary if pulmonary hypertension is suspected.

Treatment

Surgical

Premature Infants

In premature infants, surgical therapy is generally reserved for failure of COXi therapy in symptomatic patients or for those who develop contraindications to COXi therapy: NEC, renal dysfunction, and intraventricular hemorrhage. This strategy of reserving surgery for failure of medical therapy can lead to a higher incidence of NEC when compared with early surgery, although no difference in mortality has been demonstrated. Early surgical duct closure allows early institution of full oral feeding, but this does not necessarily translate into shorter hospital stay. Yet controversy regarding the indications and timing for surgical therapy remains, and variability in practice patterns have been observed.

Preoperative evaluation focuses on medical stabilization, including detection and appropriate treatment of pre-existing infections prior to surgery. Surgery for premature infants can be performed either in the intensive care unit or in the operating theater. Surgical ductal ligation is generally performed via left thoracotomy, although video-assisted thoracoscopic surgery (VATS) approach has been described, and the PDA is occluded by placement of an external clip ( Fig. 113-2 ). Preoperative imaging must exclude the presence of ductal or pulmonary artery aneurysms, which may necessitate extensive resection and vascular reconstruction rather than simple ductal ligation.

Full-Term Infants, Children, and Adults

Pharmacologic closure is ineffective in full-term infants, children, and adults, leaving surgical or transcatheter closure as the only options. Ductal closure is indicated in both symptomatic and asymptomatic patients to reduce the risks of endocarditis and pulmonary hypertension. Asymptomatic infants may undergo elective closure between 1 and 2 years of age to facilitate VATS or transcatheter closure, whereas symptomatic infants should undergo prompt evaluation and closure. The presence of cyanosis and bidirectional shunting through the PDA on echocardiography should prompt preoperative cardiac catheterization to measure pulmonary vascular resistance. If elevated pulmonary vascular resistance is unresponsive to oxygen or nitric oxide, closure is contraindicated.

Options for surgical closure in infants include thoracotomy or VATS (see Surgical Approaches ). Children and adults are candidates for closure via the transcatheter, thoracotomy, VATS, or sternotomy approaches, depending on the morphology of the PDA. Short length and large diameter of the PDA increase the risk of device embolization during transcatheter closure and bleeding during VATS closure. A severe adverse event rate of approximately 2% is seen with transcatheter closure, with younger age being a significant risk factor. To avoid the risk of recanalization, some advocate ductal division in addition to ligation in children and adults. Extensive ductal calcification increases the risk of bleeding during external ligation by VATS or thoracotomy. In these patients, median sternotomy, cardiopulmonary bypass, and closure through a pulmonary arteriotomy may be the safer alternative.

Prognosis

Operative mortality related to PDA ligation in full-term infants and children is less than 1%. Premature infants with multiple comorbidities may have hospital mortality as high as 20%. Complications of surgical ligation include left recurrent laryngeal nerve injury, bleeding, postoperative chylothorax, and development of coarctation. Asymptomatic recurrent laryngeal nerve injury can be detected in up to 7% of patients by systematic endoscopy, and the major risk factor for this injury is birth weight less than 1 kg. Symptomatic nerve injury manifested by aspiration of feeds is rare.

Introduction

Narrowing of the thoracic aorta beyond the level of the innominate artery (discrete coarctation of the aorta or transverse arch hypoplasia) represents 4% to 8% of cases of congenital heart disease, with an incidence in the general population estimated at 0.2 per 1000 live births. Bicuspid aortic valve is an associated finding in up to 50% of patients, and hypoplasia of left heart structures is relatively common. A ventricular septal defect (VSD) may be seen in 30 to 60% of patients, and it may be associated with posterior malalignment of the conal septum leading to left ventricular outflow tract obstruction. Complex congenital heart disease and associated with hypoplasia of the systemic ventricle (hypoplastic left heart syndrome, right dominant atrioventricular canal, transposition of the great arteries with hypoplastic right ventricle) may have associated coarctation that affects management. The incidence of coarctation in patients with right aortic arch is unknown, but it has been estimated to be approximately 4%.

Anatomy and Pathophysiology

The location and extent of aortic obstruction can vary from patient to patient. Discrete coarctation typically occurs just below the origin of the left subclavian artery at the insertion of the ductus arteriosus (juxtaductal coarctation). More diffuse hypoplasia of the distal arch between the left carotid artery and left subclavian artery occurs more commonly in patients with bovine arterial trunk, in which the innominate artery and the right carotid artery arise within close proximity from the proximal transverse arch. An aberrant right subclavian artery arising distal to the coarctation occurs in approximately 3% of patients.

The etiology of coarctation with hypoplasia of the distal transverse arch is not well defined, but its association with hypoplasia of left heart structures suggests common genetic, hemodynamic, or environmental mechanisms. Discrete coarctation of the aorta at the isthmus likely results from abnormal infiltration of ductal tissue onto the juxtaductal aorta. Synchronous with ductal closure, the contractile ductal tissue within the aorta constricts, resulting in luminal narrowing of the aorta and development of a posterior shelf. It is not uncommon for the aorta to appear of adequate size in the presence of a patent ductus arteriosus, yet manifest coarctation following ductal closure.

Natural History

If the coarctation is left untreated, the prognosis varies from severe heart failure in infancy to asymptomatic hypertension in older children and adults. Collateral vessels become prominent because of increased flow within the intercostal, internal mammary, and scapular blood vessels. The increased flow within these vessels can be sufficient to reduce the blood pressure gradient between the upper and lower extremities at rest. With exercise, however, the gradient may rise significantly because of the elevated vascular impedance. Upregulation of circulating catecholamines and the renin-angiotensin system leads to systemic hypertension. Left ventricular hypertrophy is a result of elevated systemic vascular resistance. Untreated coarctation is associated with a substantially diminished long-term survival, with 75% mortality by 50 years of age. Death in these patients is usually due to systemic effects of hypertension, including heart failure, intracranial hemorrhage, coronary artery disease, or aortic rupture or dissection.

Clinical Presentation

The clinical presentation varies depending on the age at presentation. Almost half of patients with coarctation will develop symptoms within the first month of life and will often have the preductal subtype of coarctation with hypoplasia of the arch. Neonates with unsuspected critical coarctation usually have systemic hypoperfusion, metabolic acidosis, and congestive heart failure manifested as tachypnea and difficulty feeding. The timing of the onset of symptoms generally correlates with constriction of the PDA, which provides systemic circulatory support for a period of time after birth. As the ductus closes, perfusion to the lower extremities and abdominal viscera becomes compromised, and end-organ failure manifests with renal dysfunction, hepatic failure, intestinal ischemia, and profound metabolic acidosis. On physical examination, prominent upper extremity and weak lower extremity pulses may be found. Neonates presenting in this manner have a high mortality without urgent intervention. With less severe degrees of coarctation, or in the presence of sufficient collateral development, symptoms may not develop until infancy or adolescence. Asymptomatic patients have a murmur or hypertension. Young adults usually demonstrate hypertension refractory to pharmacotherapy, exercise intolerance, headaches, or angina.

The classic physical findings include the presence of brachiofemoral pulse delay, diminished or absent femoral pulses, and a blood pressure gradient between the upper and lower extremities. In the presence of well-developed collaterals, there might not be a significant gradient between upper and lower extremity blood pressures. A systolic ejection murmur is audible over the base of the heart and left interscapular region. The electrocardiogram may reveal evidence of left ventricular hypertrophy in older patients.