Pulmonic Stenosis
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Introduction
This is cardiovascular disease that is common in dogs and rare in cats and large animals.
The three possible areas for pulmonic stenosis to occur are:
1. Subvalvular or subpulmonic (occurs below the valve)
2. Valvular (occurs at the valve)
3. Supravalvular (occurs above the valve)
'Most cases of pulmonic stenosis are valvular, whilst supravalvular pulomic stenosis is rare. Stenosis of the pulmonary outflow tract is the result of dysplastic changes in the pulmonic valve. Concentric hypertrophy of the right ventricle forms as a direct result of the chronic pressure overload needed to surpass the increased resistance from the stenotic pulmonary outflow tract. This concentric hypertrophy causes decreased ventricular filling during diastole and elevated right atrial pressure from the blood are unable to fill the ventricle causes atrial dilation. Tricuspid valve regurgitation can also be present and adds to the atrial pressure.
Signalment
Predisposed breeds of dog include the Miniature Schnauzer, Fox Terrier, Chihuahua, Miniature Pinscher, Labrador Retriever, Newfoundland, Mastiff, Samoyeds and Terrier Breeds.
Clinical Signs
Exercise intolerance, syncope and signs of right sided congestive heart failure (if severely affected). Sometimes the condition can be asymptomatic if only mildly affected.
Diagnosis
History and clinical signs can be indicative of heart disease. Upon physical examination, it is likely that a systolic crescendo-decrescendo ejection murmur over pulmonary artery in the left heart base will be heard. There will usually be normal femoral pulses. There may be signs of right sided congestive heart failure, such as ascites and jugular distension and jugular pulses.
Radiographic findings may include right ventricular enlargement (DV view seen at 1 o'clock), right atrial enlargement and pulmonary artery enlargement (DV view seen at 2 o'clock). Changes are seen most clearly on the 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.
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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