Unwanted Vascular Communications: Patent Ductus Arteriosus, Coronary Fistulas, Pulmonary Arteriovenous Malformations, and Aortopulmonary Collaterals

Background

The ductus arteriosus is derived from the left sixth embryologic arch and connects the origin of the left main pulmonary artery (MPA) to the aorta, just below the left subclavian artery.

During fetal life, the ductus carries the majority of the outflow of the right ventricle (RV) to the descending aorta. Spontaneous functional closure of the ductus arteriosus usually occurs after delivery by approximately 15 hours of age, with permanent closure occurring within several weeks. Persistent PDA is estimated to occur in approximately 0.8/1000 live births, exclusive of silent PDA. The prevalence of PDAs decreases with age, but the true prevalence in the adult population is unknown because many cases of hemodynamically insignificant PDA have no signs or symptoms and patients remain undiagnosed. Silent PDAs (those in whom no pathologic murmur is audible) are estimated to occur in up to 0.5% of patients referred for echocardiographic evaluation of an innocent murmur ; however, the clinical significance of these is controversial.

The clinical manifestations of a PDA are dependent upon the direction and degree of shunting across the PDA. Factors that control the direction and magnitude of the shunt across the PDA include the diameter and length of the ductus arteriosus, the pressure difference between the aorta and pulmonary artery (PA), and the systemic and pulmonary vascular resistances.

The physiologic effects of the PDA are related to the left-to-right shunt. Normally if the pulmonary vascular resistance is low, oxygenated blood from the aorta crosses the PDA into the PA. This lowers the systemic diastolic pressure and widens the pulse pressure. There is increased pulmonary blood flow with resulting increased pulmonary venous return. The left atrium (LA) may become dilated from the volume load, as may the left ventricle (LV). Dilation of the LV may result in increased ventricular end-diastolic pressure and subsequently secondary elevation in the left atrial and pulmonary venous pressures. With large left-to-right shunts, this may result in left heart failure with pulmonary edema. If untreated, a subgroup of patients may develop progressive elevation in pulmonary vascular resistance and ultimately develop irreversible pulmonary vascular disease and Eisenmenger physiology with a right-to-left shunt at the PDA.

Diagnosis and Clinical Presentation

If the shunt across the PDA is small, no signs or symptoms may be present, or a murmur heard during physical examination might be the only abnormality. Patients are typically asymptomatic. The murmur may be a soft systolic murmur best heard at the left upper sternal border or a continuous murmur. The murmur is often harsh and may have a “machinery” quality. The presence of the murmur does not necessarily imply that the PDA is hemodynamically significant, because the murmur most likely results from the jet from the PDA striking the anterior aspect of the PA. Likewise the absence of a murmur does not imply that the PDA is hemodynamically insignificant, because left heart dilation has been found even in the absence of a murmur. Chest x-ray findings may be normal with a small PDA, as may the electrocardiograph (ECG). Echocardiography in a parasternal short-axis view is diagnostic with color Doppler demonstrating the left-to-right shunt ( Video 22–1 ). Echocardiography is also used to assess the hemodynamic significance of the PDA by measuring the size of the LA and LV and to assess for signs of pulmonary hypertension. Other testing such as a computed tomography (CT) scan or magnetic resonance imaging (MRI) are usually not necessary to diagnose a PDA (although they may be helpful in situations in which the echocardiographic assessment is suboptimal) and often leads to overestimation of the size of the PDA.

Patients with moderately sized PDAs may complain of dyspnea on exertion and easy fatigability. Moderately sized PDAs result in widened pulse pressure and the continuous murmur, as described. The chest x-ray may be normal or demonstrate mild cardiomegaly. The ECG may demonstrate left ventricular hypertrophy (LVH). The echocardiogram demonstrates the PDA, as well as left atrial and ventricular dilation.

Patients with large PDAs also complain of dyspnea on exertion and fatigability and may have overt signs of left heart failure. Large PDAs result in a wide pulse pressure with a continuous murmur. A thrill from the PDA may be palpable, and the second heart sound may be accentuated. The chest x-ray demonstrates cardiomegaly and increased pulmonary vascularity. The ECG demonstrates LVH. The echocardiogram demonstrates the PDA with a dilated LA and LV. There is a low velocity diastolic flow jet in the PA, and there may be diastolic flow reversal in the descending aorta.

Large PDAs associated with the development of pulmonary vascular disease lead to a decrease in left-to-right shunt across the PDA and eventually a right-to-left shunt. This is manifest by a soft systolic or no murmur and a loud P2. The chest x-ray demonstrates findings of pulmonary vascular disease with a normal heart size and prominent central pulmonary arteries. The ECG shows right ventricular hypertrophy. There may be clubbing and cyanosis of the lower extremities because the desaturated blood from the PA is directed across the PDA into the descending aorta. Echocardiography may demonstrate a right-to-left shunt across the PDA with evidence of pulmonary hypertension. The right-to-left shunt may be difficult to appreciate on transthoracic echocardiography, and a cardiac catheterization may be indicated.

Management

The only potential indication to close a small hemodynamically insignificant PDA is prevention of endarteritis. This is a controversial topic. A recent review on this subject by Fortescue et al estimated that the risk of endarteritis associated with this type of a PDA is between 0.01% and 0.001% per year. These authors also reviewed 10 published papers on transcatheter PDA closure as well as their own institutional experience. They reported a major overall adverse event rate of 1.5%, with a minor adverse event rate of 8%. Their conclusion was that “there is no evidence to support a superior risk/benefit balance for routine closure of the very small hemodynamically insignificant PDA, and accordingly, it is difficult to justify closure of such defects simply to reduce the risk of infective endocarditis and its complications.”

According to 2008 guidelines from the American College of Cardiology/American Heart Association (ACC/AHA), routine follow-up examination every 3 to 5 years is recommended for patients with a small PDA and no evidence of left heart enlargement (Class I recommendation; Box 22–1 ).

Procedural Technique

PDAs of 2 mm or smaller at the narrowest portion are suitable for coil embolization. Coils are available in a variety of shapes and sizes ( Figure 22–1 ). PDAs larger than 2 mm in diameter may be closed with coils, but the embolization risk is higher, and multiple coils and specialized techniques may be required. Therefore for larger PDAs, device closure using the Amplatzer ductal occluder (ADO; St. Jude Medical, St. Paul, Minn.) is preferred. Ductal morphology is important, in addition to size of the ductus. The Krichenko classification is generally used for PDA morphology ( Figure 22–2 ).

Device Occlusion

The ADO ( Figure 22–4 ) is the most commonly used device to close moderate to large PDAs since approval by the U.S. Food and Drug Administration in 2003. The ADO has an aortic retention disk with an attached slightly conical-shaped body. The body tapers in diameter away from the aortic retention disk. The device is intended for implantation from a transvenous approach and is deployed through a 5F to 7F long sheath.

• 1.

  Similar to coil delivery, an aortic angiogram is performed ( Figure 22–5 ). The device is chosen so that the smaller end of the device is 2 mm larger than the narrowest diameter of the PDA. If the PDA is tubular in shape (Krichenko type C, Figure 22–6 , A ), an Amplatzer vascular plug II can be used, and also should be sized 2 mm bigger than the PDA diameter ( Figure 22–6 , B).

  
  

• 2.

  After a device is chosen, the PDA is crossed from the PA end and an appropriately sized TorqVue delivery sheath (St. Jude Medical, Plymouth, Minn.) is placed over a wire across the PDA. In many adults it is very difficult or impossible to cross the PDA antegrade from the MPA because the ductus tends to be inserted in the roof of the PA. In this situation, the ductus is crossed retrograde from the aorta with a wire, and a snare is placed transvenously into the MPA. The wire is snared in the MPA, and then the wire is pulled into the descending aorta as the snare and catheter are advanced into the descending aorta. The snare is released and removed from the body, leaving the snare catheter in the descending aorta. A 0.035-inch exchange wire is advanced through the snare catheter into the aorta, and the snare catheter is then removed. The TorqVue sheath is advanced over the wire and into the descending aorta, the wire and dilator are removed, and the sheath is flushed with saline.

• 3.

  The ADO is threaded onto the delivery cable, loaded into the delivery system, and advanced through the long sheath. The aortic retention disk is delivered into the aorta. Attention should be made not to perforate the descending aorta while doing so. The sheath tip should not be against the back wall of the aorta during advancement of the device.

• 4.

  Once the retention disk is delivered, the whole delivery system is pulled back until the disk is well seated in the aortic ampulla, and then the remainder of the device is deployed. The airway often serves as a useful landmark for the PDA on the lateral view and positioning of the device.

• 5.

  An aortic angiogram is performed before releasing the device. This will confirm device position and assess for residual shunts. Once the device is in satisfactory position, it can be released from the delivery system ( Figure 22–7 ).

  

A dose of antibiotics is given 30 minutes before coil or device placement and then every 8 hours for two more doses. Prophylaxis for subacute bacterial endocarditis (SBE) is indicated for 6 months after successful transcatheter PDA closure. If a residual shunt is still present, life-long SBE prophylaxis is needed.