Tetralogy of Fallot

Signalment

Genetics & Predisposed Breeds: Keeshonds, Miniature Poodles, Miniature Schnauzers, English Bulldogs, Wire-haired Fox Terriers

Description

The Four Defects Below Are Present in Tetrology of Fallot:

• Pulmonic Stenosis (Increases right ventricular pressure)

• Ventricular Septal Defect (Leads to shunting of blood from right to left)

• Overriding Aorta (Obtains blood from both ventricles)

• Hypertrophy of the Right Ventricle (Direct result of pulmonic stenosis; Contributes to an increase in ventricular pressure)

The outcome of the combined defects listed above depends on their severity. Usually the animal experiences pulmonary underperfusion and unoxygenated blood in the systemic circulation. Unoxygenated blood in the systemic circulation creates the hypoxic conditions necessary to stimulate the kidney’s release of the hormone erythropoietin. Erythropoietin travels to the bone marrow and stimulates an increase in red blood cell production. The increase in red blood cells can lead to polycythaemia. Overproduction of red blood cells increases the viscosity of blood leading to poor circulation and decreased oxygen delivery. Intravascular thrombi, haemorrhage, and stroke are just a few of the complications resulting from polycythaemia.

Diagnosis

History & Clinical Signs

-Lethargy

-Cyanosis

-Stunted Growth

-Exercise Intolerance

-Syncope

-Seizures

Physical Exam

-Systolic murmur (over left heart base): due to pulmonic stenosis

-Systolic murmur (over right sternal boarder): due to ventricular septal defect

-Precordial thrill (palpable over both areas)

Radiographic Findings

-Right Ventricular Hypertrophy

-Pulmonary Underperfusion

Echocardiographic Findings

-Structural Abnormalities Can Be Detected

-Doppler exam reveals the presence of a shunt and its abnormal blood flow

Electrocardiographic (ECG) Findings

-Indication of right ventricular enlargement by the presence of deep S-waves

Treatment

• Surgical

-Open Heart Surgery for complete correction (Rarely done in animals)

-Palliative Surgery: Anastamosis of either the ascending aorta or subclavian artery to the pulmonary artery improves pulmonary blood flow.

• Medical

-Exercise Restriction

-Phlebotomy (Bleeding): helps to reduce blood viscosity and improve oxygen delivery to the tissues by maintaining PCV below 65%

-Beta-blockers: reduce shunting and protect the heart from hypertrophy

Prognosis

-Guarded, but depends on the severity of defects and the level of polycythemia

-Without Treatment: Animals will live only a couple of years with poor exercise tolerance

-With Treatment: Animals can live up to seven years

From Pathology

• Pulmonic stenosis
• Right ventricular hypertrophy
• High VSD
• Overriding aorta

Commonly reported in certain breeds, E.g Keeshond, Schnauzer, Poodles and terriers.

Clinical Signs:

• Cyanotic; see severe exercise intolerance.
• Systolic murmur due to pulmonic stenosis +/- precordial thrill.
• Polycythemia due to chronic hypoxia.

Diagnosis:

• Right ventricular enlargement on radiology and ECG.
• Post stenotic dilatation of pulmonary artery on radiology and pulmonary undercirculation due to right to left shunting.
• Echocardiography may show right ventricular hypertrophy, paradoxical motion of interventricular septum (pressure RV>LV), visulaisation of VSD and overriding aorta.
• Doppler useful to image pulmonic stenosis and VSD.

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