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Pulmonic Stenosis (PS)

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Pulmonic stenosis, or PS, is considered one of the most common congenital (present at birth) heart defects in the dog, but is rare in feline patients. In general, PS refers to a narrowing at or near the pulmonic valve; however, there are variations in this defect depending upon the specific location of the narrowing (stenosis). 

Overview

Pulmonic stenosis, or PS, is considered one of the most common congenital heart defects in dogs, but is rare in feline patients. In general, PS refers to a narrowing at or near the pulmonic valve; however, there are variations in this defect depending upon the specific location of the narrowing (stenosis). The pulmonic valve is located between the right side of the heart and pulmonary arteries, which carry blood to the lungs (see below for more information). Valvular PS is the most common type of PS and is the most responsive to treatment. Valvular PS occurs when there is incomplete opening of the pulmonic valve leaflets due to malformation during development. Supravalvular PS occurs when there is a ring or ridge of tissue above the pulmonic valve causing obstruction of outflow, while subvalvular PS refers to obstruction below the pulmonic valve. The remainder of this discussion will focus on valvular PS; however, the symptoms and treatment are the same for all three types.   

 

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 through the pulmonic valve and into the main and branch pulmonary arteries, which carries blood to the lungs. The pulmonic valve closes to prevent back flow of blood from the pulmonary arteries into the right side of the heart. In the lungs, there is an exchange of gases due to respiration, in which oxygen (O2) is incorporated into 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 contractions result in the propulsion of oxygenated blood into the aorta, which ultimately carries blood back to body. 

Pulmonic stenosis occurs due to malformation of the pulmonic valve leaflets and/or surrounding tissue. The resultant narrowing causes a partial obstruction to blood flow traveling from the right side of the heart to the lungs. Due to more turbulent and accelerated blood flow through the narrowing, a heart murmur also occurs.

 

Symptoms 

The symptoms of PS can vary depending upon the degree of the stenosis and duration it has been present. In general, the greater the degree of the stenosis/narrowing, the more likely a patient will develop associated symptoms. Some patients are asymptomatic, particularly with mild PS. With more advanced disease, the defect can ultimately result in symptoms of decreased cardiac output and/or congestion upstream of the heart due to right-sided congestive heart failure. Symptoms of decreased cardiac output include lethargy, exercise intolerance, and fainting/collapse (particularly with exertion). Symptoms of right-sided CHF include abdominal distention due to fluid retention in the abdomen or difficulty breathing due to fluid around the lungs. Rarely, patients with PS can experience sudden death. 

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 pulmonic stenosis or another serious condition, a veterinary specialist is available at an ExpertVet certified or affiliated hospital.

Diagnosis

The concern for congenital heart disease typically begins by the identification of a heart murmur during one of the first routine examinations or vaccination visits. If a heart murmur is detected, an echocardiogram may be recommended to allow proper identification of the cause. This diagnostic test will allow for recognition of pulmonic stenosis, the severity of the disease, as well as if any other co-existing defects are present. Some dogs with PS have a concurrent abnormality of the tricuspid valve or a communication between the left and right atria (called a patent foramen ovale, or PFO). Additional diagnostic tests to characterize the extent of disease may be recommended including thoracic radiographs, blood pressure, and blood work. Rarely, cardiac catheterization with angiography or a computed tomography scan is necessary to fully determine the nature of heart disease present. 

Because pulmonic stenosis causes the right side of the heart to pump blood through a narrowing, the right side of the heart has to work harder and develops an increased pressure. The change in pressure experienced by the right side of the heart is referred to as the "pressure gradient," which is used to classify the severity of PS and also helps determine if intervention is necessary. In normal dogs, the pressure gradient across the pulmonic valve is less than 20 millimeters of mercury (mmHg). In dogs with mild PS, the pressure gradient is between 20 and 50 mmHg. Dogs with moderate PS have a pressure gradient between 50 and 80 mmHg and dogs with severe PS have a pressure gradient greater than 80 mmHg. Intervention is always recommended in patients with severe pulmonic stenosis, as well as dogs with moderate disease if associated symptoms are present. 

 

Treatment and Prognosis

Typically, patients with mild PS (and many with moderate PS) exhibit no symptoms and live a normal lifespan. They have a good quality of life and do not require medications or intervention. Dogs with severe PS (and some with moderate PS) are at risk for fainting, congestive heart failure, and even sudden death. The most severely affected dogs can succumb to right-sided heart failure within the first few months of life. Therapeutic options to help improve the severity of PS include balloon valvuloplasty and surgical valvulotomy. These methods are aimed at improving the degree of the stenosis by opening up the narrowing. In some patients, medications such as beta blockers are also recommended, as such therapy may reduce the incidence of associated complications. In patients that develop CHF, medications are recommended to control fluid retention; however, such treatment does not improve the severity of PS.  

BV is the preferred treatment for valvular PS as it is minimally invasive and typically affords a good clinical outcome. This procedure involves anesthetizing the patient and placing a balloon-tip catheter through a peripheral blood vessel (typically the jugular vein). Through use of a "real-time X-ray" technique called fluoroscopy, the balloon catheter is advanced through blood vessels across the stenotic valve and inflated to achieve improved valve opening. Such a procedure allows for a rapid recovery, short hospital stay, and is minimally invasive in that it only requires a small puncture or incision in the neck. Previous veterinary studies have recognized that dogs with severe pulmonic stenosis that undergo successful balloon valvuoplasty have a reduced risk of sudden death and CHF. Supra- or sub-valvular obstructions are less responsive to BV, but can be successful.  

Surgical valvulotomy is performed much less frequently, as this procedure is significantly more invasive by requiring both open-chest and open-heart techniques. Surgical valvulotomy may be necessary in extremely small patients in which the available balloon catheters are too large to be placed and/or advanced through blood vessels. Lifelong monitoring with echocardiograms is warranted in all cases of moderate or severe PS, even if intervention is performed.

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