PATENT DUCTUS ARTERIOSUS (PDA) (SEE FIGURE 34-2)
Occurrence: The ductus arteriosus is a normal part of fetal circulation. It is a vessel that connects the aorta to the pulmonary artery. Closure of the ductus usually occurs within the first 12 to 24 hours of life as a result of the increase in arterial oxygen tension and decrease in pulmonary vascular resistance. When the ductus closes, it becomes fibrous, forming the ligamentum arteriosus.
In neonates with ductal-dependent cyanotic heart lesions, prostaglandin will be administered to maintain the patent ductus arteriosus (PDA) until palliation or corrective surgery can be accomplished. In utero, the placenta was a major source of prostaglandin. In neonates with cyanotic lesions or premature infants with lung immaturity or disease, the ductus may remain patent due to the lack of a rise or delayed rise in arterial oxygen tension or due to scarring of the duct from rubella during fetal life.
Preoperative symptoms: If the ductus remains patent after birth, blood will flow from the aorta to the pulmonary artery due to decreased pulmonary vascular resistance. This left-to-right shunting will cause pulmonary overcirculation. Patients may present with congestive heart failure due to pulmonary overcirculation and left heart enlargement. Pulses will be noted to be bounding in older infants and demonstrate a widened pulse pressure as a result of a decrease in diastolic blood pressure and ventricular hypertrophy. Patients may present with tachypnea, poor feeding, and diaphoresis. Symptoms are directly proportional to the hemodynamics of the PDA.
Operative repair: If the PDA remains open and detected in the first two weeks of life, treatment options may include a prostaglandin synthetase inhibitor. After the first two weeks it may be surgically corrected by ligation or division and oversewing. It may also be closed with coil occlusion in the cardiac catheterization lab if the PDA is of the right size and configuration.
Postoperative considerations: Complications of coil occlusions in small patients include increased risk of embolization and pulmonary artery occlusion with the device, so surgical closure is preferred. Postoperative complications for surgical repair include chylous effusion and recurrent laryngeal nerve damage.
ATRIAL SEPTAL DEFECTS (SEE FIGURE 34-3)
Occurrence: An atrial septal defect (ASD) is an abnormal opening in the atrial septum. In the fourth to sixth week of gestation the common atrium is divided into two chambers. The first septum starts in the dorsal wall of the atrium and grows toward the endocardial cushions. The space between these two structures is called the ostium primum (first hole). As the first septum grows the ostium secundum (second hole) appears in its center. A second septum, the septum secundum, begins to grow, and eventually the two septa form the foramen ovale. The foramen ovale allows blood to bypass the lungs. Defective development of the septum secundum or the septum primum leads to the development of an ASD.
Normally the left atrial pressure is greater than the right atrial pressure after birth, which helps to close the foramen ovale. Incomplete closure of the foramen ovale results in an ASD. When an ASD is present there is left-to-right shunting, but in the early postnatal period shunting is minimized because the wall thickness of the ventricles is similar. As the pulmonary bed matures, the right ventricular wall thickens, pulmonary vascular resistance diminishes, and the significance of the left-to-right shunting increases. This will lead to increasing right ventricular output and workload and increased pulmonary blood flow. The chronic volume overload increases the work of the right side and right atrium and may cause enlargement of these chambers. The three most common ASDs are ostium secundum, sinus venosus, and ostium primum.
Preoperative symptoms: Patients may be asymptomatic until school age, especially with secundum ASDs and sinus venosus ASDs. Prolonged dilatation of the right atria may cause arrhythmias. Long-standing pulmonary overcirculation can lead to pulmonary vascular obstructive disease. ASDs are the most commonly missed cause of congestive heart disease. With ostium primum, symptoms include a murmur (pulmonic ejection murmur at the left upper sternal border). If there is significant mitral valve insufficiency, the patient may exhibit heart failure in infancy. Symptoms include dyspnea, fatigue, and recurrent respiratory infections. Preoperative chest x-ray will show pulmonary congestion secondary to pulmonary overcirculation.
Occurrence: Most common, accounting for 80% to 85% of ASDs. Three times more likely in females, shows significant family inheritance. Patient will show normal growth and development. The secundum ASD is located in the center of the septum.
Operative procedure: Ostium secundum ASDs may be closed during cardiac catheterization with the placement of a septal occlude, or they may be surgically repaired in combination with other defects. This is the only type of ASD that may be able to be closed with a surgical device in a cardiac catheterization lab.
Occurrence: The sinus venosus is located high in the septum near the junction of the right atrium and superior vena cava. It is often associated with total anomalous pulmonary venous return (TAPVR), with the right upper pulmonary vein draining into the right atrium.
Operative procedure: Closure includes placement of a pericardial patch with baffling of anomalous pulmonary venous drainage and coronary sinus blood to the left atrium.
Occurrence: The ostium primum defect is located in the lower end of the septum and frequently involves the atrioventricular valves, most commonly the mitral valve with a cleft on the mitral valve.
Operative repair: Surgical correction includes patch closure of the ostium primum defect, atrioventricular (AV) valve assessment, and valvuloplasty individualized to the specific patient.
Postoperative considerations: Postoperative complications include atrial dysrhythmias, heart block, residual defects, anemia, and AV valve regurgitation. If patient has arrhythmia in the operating room, patient will return from surgery with an AV sequential pacemaker, either temporary or permanent. Heart block may be due to injury to the conduction system during surgery. Mitral valve regurgitation will be demonstrated by increased left arterial pressures and low cardiac output. Chest x-ray will show pulmonary congestion.
VENTRICULAR SEPTAL DEFECT (SEE FIGURE 34-4)
Occurrence: A ventricular septal defect (VSD) is an abnormal opening between the right and left ventricles. The ventricular septum is established in the fourth to eighth week of gestation from the muscular membranous tissues that fuse with the endocardial cushions and bulbus cordis.
Preoperative symptoms: Generally a VSD shunts left to right. At birth, when pulmonary vascular resistance (PVR) is elevated, there may be minimal shunting. As the PVR and right heart pressures fall below systemic pressures, a left-to-right shunt will develop resulting in pulmonary overcirculation and detectable symptoms. VSDs are often not detected until 4 to 6 weeks of age unless they are very large. The size of the shunt will affect the patient’s clinical presentation. The larger the VSD, the greater the shunting of blood from the left to the right and the subsequent increase in signs and symptoms of congestive heart failure. Over time, the effect of excessive pulmonary blood flow will cause volume overload on the left ventricle, causing left heart enlargement. Long-standing pulmonary overcirculation will lead to the development of pulmonary hypertension.
Operative repair: Endocarditis prophylaxis is recommended for all patients with a VSD, regardless of the size. Closure of small VSDs is controversial, but arguments to close the VSD include prevention of future cardiomegaly and decreased risk of endocarditis, arrhythmias, and progressive aortic regurgitation.
Timing of the repair is critical in preventing long-term complications. Surgical closure is completed on bypass with hypothermia, and sutures or a patch are used to close the defect. Because the surgical correction is near the AV node and His bundle in many VSDs, care is taken to avoid the conduction system. Most VSDs are repaired through a right atriotomy and visualized through the tricuspid valve.
Postoperative considerations: Postoperative complications include a residual VSD, heart block, low cardiac output, and junctional ectopic tachycardia. Patients with preoperative elevated pulmonary pressures may develop right heart failure. Aortic insufficiency may develop after repair of subarterial defects and is identified by the presence of a widened pulse pressure and a diastolic murmur.
Types of VSDs are identified by the location on the septum.
Occurrence: Common atrioventricular canal is a defect resulting from the nonfusion of the endocardial cushions leading to abnormalities in the atrial and/or ventricular septum. The defect also presents with varying defects of the AV valve, including malformation or malposition of the AV valves, resulting in variable mixing. It generally involves a primum ASD, AV valve abnormalities, and a VSD. When the ventricles are of equal size, the defect is balanced. If one ventricle is larger than the other, it is an unbalanced defect.
An incomplete AV canal usually consists of a primum ASD and two AV valve orifices with a cleft mitral valve. A transitional AV canal consists of an ASD above and below the AV valves but has two distinct AV valves. Both valves, although separate from each other, are abnormal. A complete defect consists of a primum ASD, VSD in the upper ventricular septum, and a common AV valve with five leaflets. A complete AV canal (ASD, VSD, common AV valve) is prevalent in children with trisomy 21. The complete AV canal allows significant left-to-right shunting and pulmonary overcirculation.
Preoperative symptoms: Hemodynamic symptoms of an incomplete AV canal will vary by the size of the septal defect, the degree of mitral valve incompetence, and the patient’s pulmonary vascular resistance. Symptoms will vary from asymptomatic to those of a primum ASD. Once the PVR is normal, shunting from left to right will occur. If the mitral valve is insufficient, it will produce a left ventricular to right atrial shunt, increasing the load on the right heart.
The hemodynamic symptom of a complete AV canal is a significant left-to-right shunting with pulmonary overcirculation. Pulmonary resistance, systemic resistance, ventricular pressures, and myocardial compliance will affect the degree of shunting present. The patient will exhibit signs and symptoms of congestive heart failure (CHF). These children are also at increased risk for developing respiratory infections and pneumonia. Evidence of increasing pulmonary hypertension is the main indication for surgical repair.
INCOMPLETE (PARTIAL) AV CANAL (SEE FIGURE 34-5)
COMPLETE AV CANAL (SEE FIGURE 34-6)
Operative repair: Surgical repair of an incomplete AV canal is similar to repair of a primum ASD. Surgery requires bypass, hypothermia, pericardial, or synthetic patch closure of the ASD and valvuloplasty of the mitral valve. Surgery is generally recommended before 1 year of age to prevent pulmonary complications. Earlier repair is recommended in Down’s syndrome patients because of their likelihood to develop pulmonary vascular disease.
Surgical repair of a complete AV canal will require preoperative treatment for congestive heart disease (CHD) if present. Surgery is generally recommended before 1 year of age to prevent pulmonary complications. Surgery includes ASD and VSD closure and a surgical separation of the common AV valve. As in repair of the incomplete AV canal, surgery requires bypass and hypothermia. The AV valves are repaired using tissue from the common AV valve leaflets. Occasionally, mitral valve replacement may be needed. The AV valve is partially anchored to the patch and repair of the mitral or tricuspid valves. Care is taken during suturing to prevent heart block.
Postoperative considerations: In surgical repair of an incomplete AV canal, left atrium (LA) and pulmonary artery (PA) pressures will be watched for early diagnosis of pulmonary hypertension. Elevated LA pressures could indicate left heart failure. Aggressive volume resuscitation should be avoided because it may increase left AV regurgitation, decrease cardiac output, and cause hypotension.
Postoperative complications for a complete AV canal repair include heart block, arrhythmias, residual shunt, and AV valve insufficiency. Pulmonary hypertension may be treated with oxygen, sedation, alkalosis, and possibly nitric oxide. Like the incomplete AV canal repair, aggressive volume resuscitation should be avoided because it may increase left AV regurgitation, decrease cardiac output, and cause hypotension. Inotropes and afterload reduction may be used.