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== Introduction<br> ==
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== Introduction ==
The Four Defects Below Are Present in Tetrology of Fallot:
The Four Defects Below Are Present in Tetrology of Fallot:
*Pulmonic Stenosis (Increases right ventricular pressure)
*[[Pulmonic Stenosis]] (Increases right ventricular pressure)
*Ventricular Septal Defect (Leads to shunting of blood from right to left)
*[[Ventricular Septal Defect]] (Leads to shunting of blood from right to left)
*Overriding Aorta (Obtains blood from both ventricles)
*Overriding Aorta (Obtains blood from both ventricles)
*Hypertrophy of the Right Ventricle (Direct result of pulmonic stenosis; Contributes to an increase in ventricular pressure) <br>
*Hypertrophy of the Right Ventricle (Direct result of pulmonic stenosis; Contributes to an increase in ventricular pressure) <br>
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. <br>
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 [[Kidney Endocrine Function - Anatomy & Physiology#Erythropoietin|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 [[Thrombosis|thrombi]], haemorrhage, and stroke are just a few of the complications resulting from polycythaemia.
==Signalment==
Certain breeds are predisposed to the disease and these include Keeshonds, Miniature Poodles, Miniature Schnauzers, English Bulldogs and Wire-haired Fox Terriers.
== Clinical Signs<br> ==
== Clinical Signs ==
May vary depending on severity but include lethargy, cyanosis, stunted growth, exercise intolerance, syncope and seizures. <br>
May vary depending on severity but include lethargy, cyanosis, stunted growth, exercise intolerance, syncope and [[Seizure|seizures]].
== Diagnosis ==
== <br>Diagnosis<br> ==
History and clinical examination findings, plus physical examination findings. These will often include a systolic murmur (over left heart base): due to pulmonic stenosis, a systolic murmur (over right sternal boarder): due to ventricular septal defect and a precordial thrill (palpable over both areas). <br>
History and clinical examination findings, plus physical examination findings. These will often include a systolic murmur (over left heart base): due to pulmonic stenosis, a systolic murmur (over right sternal boarder): due to ventricular septal defect and a precordial thrill (palpable over both areas). <br>