Introduction

• About 6% of feline congenital heart defects.
• Cause: combination of defects - pulmonic stenosis, high ventricular septal defect (VSD), dextroposition/overriding aorta; plus right ventricular hypertrophy (physiological response).
• Signs: usually stunted and cyanotic.
• If pulmonic stenosis is mild and VSD is left-to-right shunting, patient less severely compromised ('Pink tetralogy').
• Diagnosis: radiographic signs of right-sided enlargement, cardiac murmur, echocardiography.
• Treatment: none/medical therapy/cardiac surgery, depends on severity.
• Prognosis: poor to grave.

Pathogenesis

Etiology

• Embryological developmental anomaly affecting closure of the membranous interventricular septum and differentiation of the conotruncus  - affecting the pulmonary trunk, pulmonic valve and the aorta - secondary to deviation of the outlet septum.

Predisposing factors

General

• ?None. ?Breed lines.

Pathophysiology

• Embryological developmental anomaly manifested as a membranous VSD, abnormal position of septum and pulmonic stenosis.
• Conotruncal abnormality results in a degree of dextroposition of the aorta, often with a hypoplastic pulmonary trunk.
• Right ventricular hypertrophy compensates for the pressure overload due to pulmonic stenosis.
• Increased right ventricular pressures lead to right-to-left shunting across the VSD.
• With severe dextroposition of the aorta, overriding the VSD, some right ventricular ejection is into the aorta, exacerbating the right-to-left shunting.

• Depends on severity of pulmonic stenosis and ventricular septal defect Ventricular septal defect.

Severe

• Secondary right ventricular hypertrophy  →  increased right ventricular pressure  →  shunting from right-to-left ventricle  →  cyanosis  →  hypoxia  →   hypoxic kidneys release erythropoietin  →  increased red blood cell production  →  polycythemia  →  animal incapacitated by hypoxia.

Timecourse

• Since birth.

Diagnosis

Treatment

Prevention

Outcomes