The ductus arteriosus is a normal structure that is present in the canine fetal heart. Its purpose is to divert blood from the pulmonary artery (the vessel that brings blood from the heart to the lungs for oxygenation) directly to the aorta (the vessel that delivers blood from the heart to the rest of the body). Therefore, the ductus arteriosus is present in the fetal heart to bypass the majority of canine fetal blood around, rather than through the lungs. This is necessary because the canine fetus lives in the fluid environment of the mother’s uterus, receiving oxygen from its mother’s bloodstream.
At birth, the fetus’s blood supply from the mother is cut off, and the neonate breaths air increasing circulation to its own lungs, causing the ductus arteriosus to close. With the condition patent ductus arteriosus, the ductus arteriosus does not close, causing abnormal blood flow through the heart and lungs.
The degree to which a patient is affected depends on the magnitude of the defect. This can range anywhere from a small blind pocket off the aorta which does not cause any problems, to varying degrees of abnormal blood flow through the ductus arteriosis between the aorta and the pulmonary artery. Most commonly, there is a shunt from the left to the right side of the heart , with blood from the higher pressure aorta continuously shunted to the pulmonary artery. This means an increased volume of blood is sent to the lungs which results in fluid build-up (pulmonary edema) and volume overload of the left side of the heart. This condition most commonly affects medium to toy breed dogs. Clinical symptoms of the disease include: coughing, reduced tolerance of exercise, loss of weight, and eventually, congestive heart failure. Premature death is likely without treatment.
Patent ductus arteriosus is diagnosed by history, auscultation of a “machinary” heart murmur on physical examination, cardiac enlargement and pulmonary edema on chest x-ray, and visualization of the defect with cardiac ultrasound (echocardiagram). The least invasive treatment available is to feed a coil via a catheterized large vessel into the patent ductus arteriosis to block the flow of blood through it. However, depending on the size of the patient, anatomical and other factors, not every case is a candidate for this procedure. In these cases, open heart surgery to ligate the patent ductus ateriosus closed is necessary. If the patient is reasonably stable immediately prior to treatment, prognosis tends to be fair to good with treatment.