eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiothoracic Surgery
Patent Ductus Arteriosus, Surgical Treatment
Updated: Oct 28, 2009
Introduction
The ductus arteriosus connects the main pulmonary trunk to the descending aorta distal to the origin of the left subclavian artery. In most individuals, the ductus arteriosus is located on the left side; however, if a right aortic arch is present, the ductus arteriosus may be located on the right or left side. The ductus arteriosus is very rarely bilateral. The structure varies in length and diameter. Histologically, the media of the ductus is composed of smooth muscle, and the intima is much thicker than the aorta. Contraction of this muscular media after birth causes shortening of the ductus and its functional closure. Folding of the endothelium and proliferation of the subintimal layers cause permanent closure, which usually occurs during the first 2-3 weeks of life. Persistence of a patent ductus occurs in several conditions.
Diagram illustrates the patent ductus arteriosus.
History of the Procedure
Munro initially described surgical ligation of the patent ductus arteriosus in 1907. Gross performed the first successful operation in 1939.1 Catheter-based closure of the structure was first performed in 1971.
Problem
In normal fetal circulation, the unexpanded lungs receive only 5-8% of the blood entering the pulmonary artery. The ductus arteriosus serves as the predominant route of circulation passing through the right ventricle and pulmonary artery. Approximately 55-60% of the systemic circulation passes from right to left through the ductus.
In the fetus, the oxygen tension is relatively low because the pulmonary system is nonfunctional. This, coupled with high levels of circulating prostaglandins, acts to keep the ductus open. The high levels of prostaglandins result from the little amount of pulmonary circulation and the high levels of production in the placenta.
At birth, the placenta is removed, eliminating a major source of prostaglandin production, and the lungs expand, activating the organ in which most prostaglandins are metabolized. In addition, with the onset of normal respiration, oxygen tension in the blood markedly increases. Pulmonary vascular resistance decreases with this activity. These events result in contraction of the smooth muscle within the wall of the ductus, which results in its closure. A preferential shift of blood flow occurs; the blood moves away from the ductus and directly from the right ventricle into the lungs. Until functional closure is complete and pulmonary vascular resistance is lower than systemic vascular resistance, some residual left-to-right flow occurs from the aorta through the ductus and into the pulmonary arteries.
Alterations in any one of the aforementioned steps results in persistent ductal patency, left-to-right flow through the structure, and increased pulmonary blood flow.
Frequency
A persistent ductus arteriosus has been estimated to occur in 1 in 2500-5000 live births. As an isolated lesion, it represents 9-12% of all congenital heart lesions. The female-to-male ratio is 2:1.
Etiology
The factors responsible for continued patency of the ductus arteriosus are unknown, and even the conditions that have an effect on patency are not well understood.
Prematurity or immaturity of the infant at the time of delivery contributes to the patency of the ductus. Several factors are involved, including immaturity of the smooth muscle within the structure or the inability of the immature lungs to clear the circulating prostaglandins that remain from gestation. These mechanisms are not fully understood. Conditions that contribute to low oxygen tension in the blood, such as immature lungs, coexisting congenital heart defects, and high altitude, are associated with persistent patency of the ductus.
The incidence of rubella infection in the first trimester of pregnancy, particularly through 4 weeks' gestation, associated with patent ductus arteriosus is very high (£ 85%).
Incidence of patent ductus arteriosus is as much as 2-4% in siblings of patients with the condition. A socioeconomic association without a racial factor has also been observed with patency; an increased incidence of patients with patent ductus arteriosus appears to arise from lower socioeconomic origins.
Pathophysiology
With patency of the ductus and a decrease in pulmonary vascular resistance to below the level of systemic vascular resistance, blood flows from the aorta into the pulmonary artery through the ductus, resulting in a left-to-right shunt. The flow occurs through systole and diastole. This combination of blood passes through the lungs, into the left atrium, into the left ventricle, and back into the aorta. The result is an increased volume load on the left atrium and left ventricle. The increase in left ventricular stroke volume is proportional to the size of the ductus.
The increased left ventricular stroke volume and the central runoff from the aorta into the pulmonary artery results in a widened pulse pressure.
An absolute increase occurs in the total circulating volume of the patient, which is proportional to the amount through the left-to-right shunt. Pulmonary engorgement results with decreased pulmonary compliance. The reaction of the pulmonary vasculature to the increased blood flow is unpredictable.
The amount of blood that flows through the ductus is related to the size and shape of the structure and to the differences between the systemic and pulmonary resistances. The wider and shorter the ductus, the greater the blood flow through it. Higher systemic pressures provide a higher driving force behind the blood flowing through the structure. The lower the pulmonary resistance, the less the impediment affects ductal flow. Conversely, higher pulmonary vascular resistance can sometimes reverse the flow through the patent ductus arteriosus.
Presentation
No typical clinical history is observed in patients with patent ductus arteriosus. Most patients are asymptomatic and are found to have a heart murmur on physical examination. At times, the patient may report decreased exercise tolerance or pulmonary congestion in conjunction with a murmur. Patients can present at any age. However, 3-week to 6-week-old infants can present with tachypnea, diaphoresis, inability or difficulty with feeding, and weight loss or no weight gain.
Patients usually appear well and have normal respirations and heart rates. A widened pulse pressure may be noted when the blood pressure is obtained. Suprasternal or carotid pulsations may be prominent.
A continuous machinery murmur is the hallmark physical finding of patent ductus arteriosus. The murmur begins shortly after the first heart sound, peaks at approximately the second heart sound, and diminishes through diastole. The murmur may be local or widely radiate, and it may vary in intensity from very soft to grade 6. A thrill may be palpated. Often, a left ventricular heave or lift may be felt on palpation of the chest. The second heart sound is increased in intensity and widely split because of the increased pulmonary blood flow. In patients with a larger ductus, a diastolic rumble may be heard. The peripheral pulses are prominent and bounding in small patients with a large ductus.
Indications
Congestive heart failure is an indication for closure of the patent ductus arteriosus in infancy. If medical therapy is ineffective, urgent intervention to close the structure should be undertaken. All patent ductus arteriosus should be closed because of the risk of bacterial endocarditis associated with the open structure. Over time, the increased pulmonary blood flow precipitates pulmonary vascular obstructive disease, which is ultimately fatal.
Relevant Anatomy
In the normal heart with a left aortic arch, the patent ductus arteriosus forms a connection between the pulmonary artery and the aorta, just distal to the origin of the left subclavian artery. It passes from the anterior aspect of the pulmonary artery to the posterior aspect of the aorta. Typically, the ductus has a conical shape with a large aortic end tapering into the small pulmonary connection. The ductus may take many shapes and forms, from short and tubular to long and tortuous. An anatomic marker of the ductus is the recurrent laryngeal nerve, which encircles the left subclavian artery and can be found adjacent to the ductus.
Contraindications
Relatively few contraindications to closure of the patent ductus arteriosus are recognized. Clearly, attention must be paid to the existence of other congenital heart lesions that impair pulmonary blood flow. In these patients, all attempts should be made to preserve ductal flow until a more permanent palliative shunt can be constructed or definitive repair can be undertaken. Contraindications to catheter-based closure currently involve the size of the patient. Very small premature infants still require surgical closure. Contraindications to surgical closure include concurrent uncontrolled sepsis and an inability of the patient to tolerate general anesthesia.
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References
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Further Reading
Keywords
patent ductus arteriosus, PDA, persistent ductus arteriosus, aortopulmonary connection, heart defect, cardiac defect, pediatric cardiac surgery, catheter-based closure of PDA, thoracotomy, PDA closure, treatment, diagnosis
