Tetralogy of Fallot is a rare congenital defect of the heart with 3 separate developmental abnormalities, and one compensatory change :
Very occasionally there may be no signs, but usually affected animals show exercise intolerance , cyanosis of visible mucous membranes, fainting (syncope) , and retarded growth rate are seen. A compensatory increase in red blood cells (called polycythemia) is sometimes seen which causes the membranes and tongue to appear very dark - even black.
Auscultation - pulmonic stenosis murmur. Ventricular septal defect murmur.
ECG - changes consistent with right ventricular enlargement * NOTE A Provet video on "ECG Interpretation" is available form the Multimedia Shop GO HERE.
X-rays - Heart size may be normal, or have right-sided enlargement. Small, less radiodense than normal pulmonary blood vessels, and a bulge in the aorta may be seen.
Echocardiography - shows most of the abnormalities
Catheterisation and angiography - shows de-oxygenated blood shunting from the right ventricle into the aorta.
Surgically a subclavian artery can be anastomosed to a pulmonary artery to improve pulmonary perfusion, and oxygenation of blood.
Medical treatment using b -blockers (e.g. propanolol 0.3-1.0mg/kg/tid) may help minimise the secondary hypertrophy by reducing ) workload on the heart.
Low dose aspirin may help reduce the likelihood of thromboembolism due to the polycythemia, and fluid therapy may also be needed to dilute the high packed cell volume (PCV) caused by the polkycythemia - the aim is to keep the PCV below 60%.
Without surgery the prognosis is very poor. Sudden death is common.
Surgery can increase life-expectancy in dogs to 3-4 years
Updated October 2013
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