Patent Ductus Arteriyozus

Patent ductus arteriosus (PDA) is a persistent communication between the aorta and the left pulmonary artery that should have closed after birth but has instead remained open. This communication usually lies just distal to the left subclavian artery, one of the main arteries supplying the left arm. PDA may occur in association with various congenital heart defects, although in adults it is usually an isolated finding.

This communication between the two great arteries arising from the right and the left ventricles is patent in every individual during intrauterine life, and it usually closes spontaneously within the first days after birth. The closure rate is lower in premature infants, although delayed spontaneous closure is increasingly seen in these infants. In term infants in whom the duct does not close at the expected time, later spontaneous closure is not usually observed. In such patients, part of the oxygenated blood that should be delivered to the body passes through the persistent duct into the lungs. Pulmonary artery pressure then rises progressively and, as the volume of blood returning from the lungs to the left heart increases, the left ventricle has to work harder and gradually fails.

In adults, PDA produces a left-to-right shunt between the aorta and the pulmonary artery and results in volume overload of the left ventricle. In moderate and large ducts, pulmonary artery pressure rises and pulmonary arterial hypertension develops. In patients who reach adulthood with a moderate PDA, either volume overload or pulmonary hypertension may be the predominant feature.

In adult patients with a large PDA, shunt reversal is usually present: deoxygenated blood mixes completely with the oxygenated blood, and the undesirable condition known as Eisenmenger syndrome, characterised by cyanosis, develops in adult life. In these large ducts, oxygenation of the upper extremities is normal whereas oxygenation of the lower extremities is reduced; the skin of the arms is normal in colour, while cyanosis is frequently present in the legs. This pattern is termed differential cyanosis.

The clinical presentations of adult patients with PDA include the following:

• Small duct with no left ventricular volume overload (normal left ventricle) and normal pulmonary artery pressure (PAP) — generally asymptomatic.
• Moderate PDA with predominant left ventricular volume overload: a dilated left ventricle with normal or reduced function, which may present as left heart failure.
• Moderate PDA with predominant pulmonary arterial hypertension (PAH): a pressure-overloaded right ventricle, which may present as right heart failure.
• Large PDA: Eisenmenger physiology with differential hypoxaemia and differential cyanosis — normal skin colour and normal oxygenation in the upper extremities, with reduced oxygenation and cyanosis of the lower extremities, and sometimes of the left arm as well.

Patients with a PDA carry a potential risk of endarteritis — inflammation of the vessel wall caused by the high-velocity jet through the duct — although this risk appears to be low. Marked dilatation and aneurysm formation of the duct is a rare complication; in this situation the aneurysm may compress the left main coronary artery, which supplies the anterior wall of the heart.

How is the diagnosis made?

In adults, the diagnosis of PDA is readily established by echocardiography, a highly developed form of ultrasound imaging. Transthoracic echocardiography (TTE), performed simply by placing an ultrasound probe on the anterior chest wall, demonstrates the communication between the aorta and the pulmonary artery and allows its site and diameter to be defined. Once PDA has been diagnosed, the examination may be supplemented by transoesophageal echocardiography (TEE), in which the probe is swallowed and positioned in the oesophagus. The best method for defining the various morphological types of PDA, however, is aortic angiography, or aortography, performed by injecting contrast medium into the aorta. Although computed tomography and magnetic resonance imaging also give good results, aortography readily defines the origin, the type and the length of the duct, as well as the diameters of its distal and proximal segments. In our clinic, TTE and aortography are performed in every patient with suspected PDA.

How is transcatheter (device) closure performed?

The veins in the groin return the deoxygenated blood of the legs and of the region below the groin to the right heart through the large vein known as the inferior vena cava. The groin artery is one of the main vessels through which we reach the aorta and, from there, the left ventricle. In the catheterisation laboratory, the femoral artery and the femoral vein are punctured with a fine needle, and two sheaths are placed, one in the artery and one in the vein. Through the sheath in the left femoral artery, the aorta is reached with a catheter and with dedicated atraumatic guidewires. The communication between the aorta and the pulmonary artery is then reached, the duct is crossed from the aortic side, and the wire is advanced as far as the middle of the pulmonary artery.

Through the sheath in the right femoral vein, a dedicated snare is advanced through the inferior vena cava and the right ventricle into the pulmonary artery, and is used to capture the wire that has previously been passed through the PDA. The captured wire is pulled out through the venous sheath, so that an arteriovenous wire loop is created. This loop serves to improve the intracorporeal course and the stability of the delivery system that will carry the device used to close the PDA.

Once the arteriovenous loop has been established, the delivery system of the PDA closure device is advanced from the right femoral vein over this loop. After the pulmonary artery has been reached, the system is passed through the duct and advanced into the aorta. With the system stabilised in the aorta, the wire forming the loop is withdrawn. Under fluoroscopic and two- or three-dimensional echocardiographic guidance, the distal part of the closure device — which may be likened to a plug — is opened on the aortic side. The system is then withdrawn slightly further, so that the waist of the device is seated within the communication; if a double-disc device is being used, the second disc is also deployed and the communication is closed. Once complete seating of the device has been confirmed by a dedicated manoeuvre, it is released from the delivery cable and left in place. If a single-disc device is used, the disc is first fixed on the aortic side, and the body and the distal part of the device are then extended so as to close the communication before release. After the procedure, the surfaces of the device become covered spontaneously by the body's own surface lining, the endothelium, within approximately 6 months to 1 year.

Are there any risks associated with the transcatheter method or with the closure devices?

The complications of this percutaneous treatment are far less frequent than those of open surgery. In adults, dense calcification in the region of the PDA may create difficulties for surgical closure. Even in the presence of other associated cardiac lesions for which open surgery is indicated, device closure remains the preferred method of closing the duct, and in the majority of adults it can be performed successfully with a very low complication rate. Surgery should be reserved for patients whose duct is too large for device closure, or whose anatomy is unsuitable, for example because of aneurysm formation. Complications that may arise during open surgery, such as serious bleeding, the complications of prolonged anaesthesia and injury to vessels and cardiac structures, are not frequently encountered during device closure of a PDA. The cosmetic advantage of the procedure is also clear, since it is carried out without opening the chest, using only needles and sheaths placed in both groins.

Most of these devices are manufactured from nitinol, a special shape-memory metal. Apart from patients with nickel allergy, no side effect of the devices has been reported, and platinum-coated closure devices are also among those available to us. During procedures performed by operators without specific training in this field, however, the device may be dislodged and embolise into the cardiac chambers if adequate measurements have not been made or if an inappropriate device has been selected. For such situations, dedicated snares have been developed with which the device can be captured inside the body and retrieved easily. Other complications, such as bleeding, air embolism and collection of blood around the heart (pericardial effusion or tamponade), may occur during the procedure, although they are extremely rare compared with open surgery. For these reasons, both the European and the American cardiology guidelines recommend transcatheter closure as the first-choice treatment in patients with PDA.