Introduction

• Common congenital disease: 11-32% of congenital heart disease in dogs.
• Usually in smaller breed dogs; uncommon in cats.
• Cause:
  • Obstruction to flow anywhere from right ventricular outflow tract to main pulmonary artery. Most commonly valvular but can be subvalvular or supravalvular.
  • Aberrant coronary artery can result in subvalvular stenosis in Bulldogs and Boxers.
• Signs: depend on severity - subclinical → syncope on exertion or excitement; right-sided congestive heart failure.
• Diagnosis: echocardiography, angiocardiography.
• Treatment: none if mild, beta-blocker and/or valvuloplasty if severe.
• Prognosis: good if mild, fair if severe.
  Print off the owner factsheet Congenital heart disese - pulmonic stenosis to give to your client.

Pathogenesis

Etiology

• Hereditary failure of valves to form properly from endocardial tubes.
• Most commonly valvular:
  • Type A: fusion of valves, mild to moderate thickening of valves, normal pulmonic valve annulus, common post-stenotic dilatation.
  • Type B: marked thickening of valves, immobile valves, hypoplasia of pulmonic valve annulus, uncommon post-stenotic dilatation.
  • Often a combination.
• Less commonly infundibular, subvalvular or supravalvular stenosis.
• Probably polygenic mode of inheritance.
• Bulldogs, Boxers and Bullmastiff can have a coronary artery anomaly causing subvalvular stenosis.

Predisposing factors

• In-breeding.

Pathophysiology

• Obstruction to right ventricular outflow → compensatory right ventricular hypertrophy. Infundibular hypertrophy can contribute to dynamic right ventricular outflow tract obstruction.
• Myocardial oxygen demand is increased because increased pressure generated in RV to overcome osbtruction to flow, myocardial oxygen supply is decreased because coronary artery supply may not increase in proportion to hypertrophied right ventricular myocardium → myocardial hypoxia → ischemia, fibrosis → arrhythmia, myocardial dysfunction → syncope, sudden death, right-sided congestive heart failure.
• Significant tricuspid valve regurgitation (eg concurrent tricuspid valve dysplasia Heart: tricuspid valve dysplasia) and/or increased right ventricular filling pressures due to diastolic dysfunction secondary to hypertrophy → increased right atrial pressures →  may develop right-sided congestive heart failure.
• If concurrent patent foramen ovale, ASD Heart: atrial septal defect or VSD Heart: ventricular septal defect increased RV pressures may result in right-to-left shunting and cyanosis.

Timecourse

• From birth.

Diagnosis

Treatment

Prevention

Outcomes