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.
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.
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.