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Patent Ductus Arteriosus

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A patent ductus arteriosus, or PDA, is considered the most common congenital (present at birth) heart defect in dogs. This defect occurs due to failure of the ductus arteriosus, a normal blood vessel present in the developing fetus, close to or just after birth. As a result, the ductus arteriosus remains open, or ‘patent.’

Overview

A patent ductus arteriosus, or PDA, is considered the most common congenital heart defect in dogs. This defect occurs due to failure of the ductus arteriosus, a normal blood vessel present in the developing fetus, close to or just after birth. As a result, the ductus arteriosus remains open, or ‘patent.’ This results in significantly increased blood volume traveling between the main great vessels that exit the heart, the aorta, and the pulmonary artery. This ultimately causes increased blood flow through the lungs and back to the left side of the heart.

If uncorrected, this defect typically results in left-sided congestive heart failure within 12 – 18 months of age, with associated symptoms of labored breathing, coughing, and/or collapse. With appropriate recognition and intervention, however, most patients with a treated PDA live a normal lifespan. 

Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from patent ductus arteriosus or another serious condition, a veterinary specialist is available at an ExpertVet certified or affiliated hospital.

 

Cause

In order to understand how this disease may affect your pet, it is important to understand how blood normally travels through the heart. As blood drains from the body back to the heart, it first enters the upper chamber on the right side of the heart referred to as the right atrium. Following the contraction of the right atrium, blood flows through the tricuspid valve and into the lower right heart chamber, called the right ventricle. Following a right ventricular contraction, blood is pumped into the pulmonary artery, which carries blood to the lungs.

In the lungs, there is an exchange of gases due to respiration, in which oxygen (O2) is incorporated into the bloodstream and the waste gas carbon dioxide (CO2) is released. Following circulation through the lungs, oxygenated blood then drains through the pulmonary veins and into the left side of the heart. As this occurs, blood enters the left atrium and is pumped through the mitral valve and into the left ventricle. Left ventricular contraction results in the propulsion of oxygenated blood into the aorta, which ultimately carries blood back to body. 

In a developing fetus, the ductus arteriosus functions to shunt blood from the pulmonary artery to the aorta, bypassing non-functional lung tissue. Soon after birth, the lungs expand as breathing begins and the ductus arteriosus should close, allowing blood to flow through the now functional lung tissue. In some patients, the ductus remains open, or ‘patent.’ As a result, communication remains between the aorta and the pulmonary artery, allowing increased blood flow between these vessels, through the lungs, and ultimately back to the left side of the heart. 

 

Symptoms 

The symptoms of a PDA can vary depending upon the defect's size and the patient's age. The larger the size of a PDA and the longer it is present, the greater the blood volume traveling through the lungs and back to the left side of the heart. Over time, typically within 12 – 18 months of life, the left side of the heart may not be able to keep up with the increased blood volume needing to be pumped, and left-sided congestive heart failure (L-CHF) can develop. This results in fluid retention within the lungs and associated symptoms such as coughing, labored breathing, and severe lethargy.

Unfortunately, L-CHF is a progressive disorder that affected patients ultimately succumb to. Rarely, a PDA can cause blood flow in the opposite direction (from the pulmonary artery to the aorta) due to the development of a condition referred to as pulmonary hypertension. In this case, sufficient blood never reaches the lungs to pick up oxygen and signs of systemic hypoxemia develop with severe weakness, lethargy, intolerance to exercise, and episodes of collapse (particularly with activity).

 

Treatment and Prognosis

If left uncorrected, the majority of dogs with a PDA will develop congestive heart failure and die from their disease by 12 – 18 months of age. With proper recognition and treatment, however, dogs with an uncomplicated PDA that is corrected typically live a normal lifespan.

Treatment of a left-to-right PDA involves closure of the defect via surgery or a catheter-based approach. Most pets with this condition are candidates for interventional occlusion of the defect. This is a minimally invasive procedure that involves anesthetizing the patient and placing a catheter into the femoral artery, a blood vessel within the leg. Through use of a real-time X-ray technique called fluoroscopy, an occluding device is advanced from the femoral artery and into the PDA, blocking flow through the PDA. Such a procedure allows for rapid recovery, a short hospital stay, and is minimally invasive in that only a small surgical incision in the leg is required.

If your pet is too small or the defect is of a shape not amenable to interventional repair, surgical closure can be performed. This involves making an incision in the chest and direct ligation of the defect with a suture. Although this is considered open-chest surgery, it does not involve open heart techniques. The success rate of a surgical procedure compared to an interventional one is considered equal. 

Typically, a recheck evaluation is performed two – four weeks following the closure of the PDA. Follow-up evaluations performed thereafter are dependent upon the severity of the PDA and the success of closure; however, in many patients they are not required.

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