Congenital Heart Disease
Congenital heart disease is a general term used to describe cardiac defects present at birth. The congenital defect may be an abnormally formed valve, heart chamber, or great vessel entering or leaving the heart. An abnormal communication between heart chambers or vessels would also fall in this category. The most common congenital cardiac defects seen in dogs include patent ductus arteriosus, pulmonic stenosis, and subaortic stenosis.
Patent Ductus Arteriosus (PDA)
A PDA is caused by the failure of a fetal blood vessel, the ductus arteriosus, to close after birth. This vessel connects the aorta and the main pulmonary artery and remains open in utero to allow blood to bypass the developing fetal lungs. At birth this vessel should close to allow for normal blood flow through the heart. If this vessel does not close, the left side of the heart can become overcirculated leading to enlargement of the heart and left sided, congestive heart failure. An echocardiogram, a heart ultrasound, is needed in order to diagnose a PDA. Thoracic radiographs are also useful to determine the status of the lung vessels. Treatment options for PDA include closure of the vessel by a minimally invasive transcatheter procedure or by surgical ligation of the vessel.
Blood passes through the pulmonary valve as it travels from right side of the heart to the lungs where the blood is saturated with oxygen. Stenosis (narrowing) either involves the region beneath the pulmonary valve, the pulmonary valve itself, or the region above the pulmonary valve. The most common form of pulmonic stenosis that we see is at the valve. This abnormality makes it harder for the right side of the heart to pump blood to the lungs resulting in hypertrophy (thickening) of the right ventricular walls. As less oxygen reaches the thickened heart muscle the patient becomes predisposed to abnormal heart rhythms and sudden death can occur. Other symptoms that may be seen with this disease include syncope (collapse) and right sided, congestive heart failure.
Pulmonic stenosis is more common in smaller breed dogs but is occasionally seen in large breeds. The best test to diagnose this condition is an echocardiogram. Treatment options for pulmonic stenosis depend on the severity of the disease. Dogs with mild pulmonic stenosis often require no treatment and go on to live a normal life. Dogs with moderate to severe disease may require an interventional procedure called a balloon valvuloplasty to open up the stenotic pulmonary valve. Treatment with a group of drugs known as Beta blockers is often instituted to manage symptoms.
Subaortic stenosis is a heritable defect and is more common in larger breed dogs. Boxers, Bull Terriers, German Shepherds, Golden Retrievers, Newfoundland, Rottweiler and Mastiff breeds are predisposed. The stenosis or narrowing is caused by a ridge of tough connective tissue that develops beneath the aortic valve. The severity of the stenosis depends on the amount of abnormal tissue present. Increasing severity causes the left side of the heart to work harder to pump blood through the narrowed passage and out to the body. Excessive work results in thickening or hypertrophy of the muscle in the largest chamber of the heart, the left ventricle, and decreased oxygen delivery to the heart muscle. A thickened left ventricle predisposes the animal to developing abnormal heart rhythms, and sudden death is a potential outcome of this disease.
The degree of stenosis can change during the first year of life, and a dog diagnosed with mild disease at 3 months can have severe disease at 1 year of age. We always recommend a follow-up echocardiogram at one year of age to monitor for any ongoing changes. Dogs with mild subaortic stenosis require no treatment. Dogs with moderate to severe disease usually require medical management with drugs known as Beta blockers. Dogs with subaortic stenosis are at a higher risk for infection of the aortic valve, and prophylactic antibiotics are recommended prior to surgery or dental procedures.