Patent Ductus Arteriosus (PDA) is a congenital disease where a once necessary fetal structure persists after birth causing significant hemodynamic alterations. In the fetal life, the ductus arteriosus is a conduit for oxygenated blood between the pulmonary artery and the descending aorta. Oxygen rich blood from the maternal circulation is present in the fetal right heart (which is oxygen poor in the adult) and travels through the pulmonary artery through the ductus arteriosus to the aorta to supply oxygen rich blood to the fetal systemic circulation. This conduit allows for oxygen rich blood to bypass the non-functional, high-pressured fetal lungs and supply the fetal circulation with oxygen more efficiently. As pulmonary pressures decrease dramatically at birth, this conduit for blood between the pulmonary artery and aorta normally should close. As the name PDA implies, this conduit remains open. Consequently, in the adult circulation the pressures in the aorta are higher in the pulmonary artery and blood follows the pass of least resistance from the aorta through the PDA to the pulmonary artery during both systole and diastole.
This scenario sets up a circuit for pulmonary overcirculation with blood that should be expelled from the aorta during systole rushing into the pulmonary artery and blood running off during diastole into the pulmonary artery, the pulmonary vasculature and once again into the left side of the heart. The end result is increased blood volume within the left side of the heart and eccentric hypertrophy of the left ventricle ensues. This volume overload of the left heart results ultimately in left-sided heart failure characterized classically with pulmonary edema secondary to left atrial enlargement and pulmonary venous congestion. A classic continuous holosystolic basilar heart murmur often described as machinery is heard in puppies and sometimes kittens. Femoral pulses are bounding due to the diastolic runoff of blood that occurs making a larger difference between systolic and diastolic pressures pulse pressures.
This disease occurs most frequently in dogs with collies, toy and miniature poodles, German shepherds, Pomeranians, Shetland sheep dogs, Yorkshire terriers, Maltese, English springer spaniels and keeshonds being overrepresented breeds. This disease can be completely cured with interventional minimally invasive technique or with surgical ligation. Rarely, a reverse PDA or right-to-left shunting can occur. This scenario leads to oxygen poor blood leaving the pulmonary artery through the ductus to the descending aorta due to abnormally high pulmonary pressures. Consequently, segmental cyanosis in the distal body is evident, usually no murmur is present and polycythemia results secondary to decreased renal perfusion. A split second heart sound may be auscultated due to separation between aortic valve closure and late pulmonic valve closure because of pulmonary hypertension.
Clinical signs of a PDA are usually not observed by the owner until the animal is in congestive left-sided heart failure. Clinical signs of left heart failure may be subtle such as increased respiratory rate at rest to mild decreases in activity or exercise intolerance.
Other clinical signs may include coughing, not sleeping through the night, coughing more at night or decreased appetite. Signs may progress to coughing up pink-tinted foam to fulminate respiratory distress. Signs of right-to-left PDAs include differential cyanosis, rear limb collapse during exercise and non-specific neurological signs.
This disease can be completely cured with interventional minimally invasive technique or with surgical ligation. The procedure whether surgery or interventional technique should be performed as soon as the pet weighs enough for the procedure. Interventional methods for closure of a PDA include the implantation of ductal occluders or coil embolization. These techniques are minimally invasive but require a weight 0f 2.5 kgs in order to be performed. Surgical ligation of the ductus can also be performed through a thoracotomy. Surgery is more invasive but can be performed in animals over 1 kg. There is no surgical or interventional technique for closing a right-to-left PDA, in fact closure could kill the animal. Treatment usually involves phlebotomy to remove the excess blood and improve clinical signs. Additionally, administration of hydroxyurea to decrease red blood cell production can also be used.