Pulmonic Stenosis

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Introduction

Pulmonic stenosis (PS) is one of the three most common congenital cardiac defects in dogs. It is much less common in cats, and is usually recognised in association with other congenital cardiac defects in this species.

Pulmonic stenosis may be subvalvular/infundibular (occurs below the valve), valvular (occurs at the valve) or Supravalvular (occurs above the valve). Most cases of PS in the dog are valvular, whilst supravalvular PS is rare.

Subvalvular (infundibular) PS is defined as a fibrous or fibromuscular diaphragm below the pulmonic valve or at the os infundibulum, or a more diffuse and extensive area of fibromuscular hypertrophy creating more of a tunnel or hour-glass deformity of the infundibulum.

Valvular PS can be further classified into type A or type B, based on valvular morphology. Type A cases have a normal pulmonary annulus diameter and type B cases have a narrow pulmonary annulus diameter, often accompanied by hypoplasia of the pulmonary trunk. Type A cases are more likely to show a post-stenotic dilatation.

Concentric hypertrophy of the right ventricle develops as a consequence of the chronic pressure overload resulting from obstruction to right ventricular outflow. Right ventricular hypertrophy may cause an infundibular narrowing of the right ventricular outflow tract (RVOT), exacerbating the stenosis and resulting in a dynamic component to the obstruction. A further consequence of right ventricular hypertrophy is reduced right ventricular diastolic filling and therefore elevated right atrial pressures with resultant right atrial dilation.

In Bulldogs, PS may be complicated by coronary artery anomalies.

Signalment

Predisposed breeds of dog include the Miniature Schnauzer, Cocker Spaniel, Fox Terrier, Chihuahua, Miniature Pinscher, Labrador Retriever, Newfoundland, Mastiff, Boxer, Samoyed and English and French Bulldog.

History and Clinical Signs

A murmur is usually detected at the initial health check or primary vaccination.

Clinical signs include exercise intolerance, syncope and signs of right sided congestive heart failure (if severely affected). Animals may be asymptomatic.

Diagnosis

Physical Examination

  • Left-sided, systolic murmur with point of maximal intensity over the heart base
  • Grade of murmur correlates with severity of stenosis for fixed obstructions
  • Apex beat may be more palpable on the right hemithorax than the left if severe right ventricular hypertrophy is present.


There may be signs of right sided congestive heart failure, such as ascites and jugular venous distension and hepatojugular reflux.

Thoracic Radiographs

Radiographic findings may include right ventricular enlargement (seen at 1 o'clock on a dorsoventral view), right atrial enlargement and pulmonary artery enlargement (seen at 2 o'clock on a dorsoventral view).

Echocardiographic findings may include right ventricular hypertrophy, poststenotic dilation of the pulmonary artery and abnormal pulmonic valve if the stenotic area is valvular. Doppler can be used to measure the pressure in the stenotic area and visualize abnormal flow.

Electrocardiographic (ECG) signs include right ventricular hypertrophy (tall P waves, deep S waves, deep Q waves, right axis deviation).

Angiography may also be used to identify the defect.

Treatment

The pressure gradient between the right ventricle and the pulmonary artery can be used to decide between medical and surgical management.

In mild to moderate cases, if there are no clinical signs then no treatment is needed.

In severe cases, if the pressure gradient is greater than 100mmHg, an invasive procedure may need to be performed. Possible options for surgery include a balloon valvuloplasty (done if pulmonic leaflets are fused) or surgical repair (done when more complex lesions and obstructions are present): valvulotomy, pericardial patch graft.

If signs of right-sided heart failure are present, these should be managed medically with diuretics and vasodilators.

Prognosis

Mild to moderate cases have a good prognosis. Severe cases have a guarded prognosis.


Pulmonic Stenosis Learning Resources
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References

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) W.B. Saunders Company

Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier




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