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Pulmonic Stenosis

By Sandra P. Tou, DVM, DACVIM, North Carolina State University

Pulmonic stenosis is common in dogs and infrequent in cats. It results in obstruction to right ventricular outflow due, in most cases, to dysplasia of the pulmonic valve cusps. Although the valvular form is most common, stenosis can also occur in the subvalvular region (infundibulum) or in the supravalvular area. Breed predilections for valvular pulmonic stenosis include English Bulldogs, Boxers, Beagles, Boykin Spaniels, and terriers. Supravalvular pulmonic stenosis is uncommon and may be most often seen in Giant Schnauzers.

Pathophysiology:

The right ventricle must generate increased pressure during systole to overcome the stenosis, which in moderate to severe cases can lead to dramatic right ventricular concentric hypertrophy and dilatation. As the right ventricle hypertrophies, ventricular compliance diminishes, leading to increased right atrial pressure and venous congestion. The turbulent jet of blood flow across the stenosis deforms the wall of the main pulmonary artery, resulting in a poststenotic dilatation. In severe cases, right-side congestive failure may be noted. Concurrent tricuspid valve dysplasia is sometimes noted in animals with pulmonic stenosis. Anomalous coronary artery development has been documented in some affected animals with pulmonic stenosis such as English Bulldogs and Boxers. Most commonly, the left main coronary artery originates from the right coronary artery and encircles the right ventricular outflow tract.

Clinical Findings and Treatment:

Affected animals may have a history of exercise intolerance and failure to thrive. Right-side CHF may be present and is characterized by ascites or peripheral edema. A prominent ejection-type systolic murmur is present and heard best at the pulmonic valve area (left base). A corresponding precordial thrill may be present. Jugular distention and pulsations may also be present. Electrocardiography will demonstrate evidence of right ventricular enlargement (deep S waves in lead II) in many cases. Radiographic abnormalities include right ventricular enlargement, dilatation of the main pulmonary artery, and diminished pulmonary perfusion. Echocardiography is indicated to obtain a definitive diagnosis and may demonstrate right ventricular hypertrophy and dilatation, thickened and relatively immobile pulmonic valve cusps, and turbulent blood flow across the stenosis. In a few cases, supravalvular or discrete subvalvular stenosis can be noted. Pulmonic insufficiency can sometimes be seen in dogs with pulmonic stenosis. The velocity of blood flow across the stenosis is used to assess the severity of disease and determine the need for intervention. Animals with moderate or severe pulmonic stenosis can benefit from balloon valvuloplasty or surgical intervention (valvulotomy, patch grafting, partial valvulectomy, or conduits). Balloon valvuloplasty is a minimally invasive and highly effective treatment option. Some animals are medically managed with a β-blocker (eg, atenolol) alone or in conjunction with balloon valvuloplasty. Congestive heart failure should be medically managed if present. Similarly, the presence of supraventricular or ventricular arrhythmias warrants therapy with the appropriate antiarrhythmic drug(s).

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