Commonest cyanotic congenital heart disease in children above the age of two years constituting almost 75 % of all blue patients.Four constituents of tetralogy as described originally by Fallot consist of :-1. Ventricular septal defect (VSD)2. Pulmonic stenosis3. overriding or dextroposed aorta, and4. Right ventricular hypertrophy

Physiologically the pulmonary stenosis causes concentric RVH without cardiac enlargement and an increase in right ventricular pressurewhen the right ventricular pressure is as high as the left ventricular or the aortic pressure, a right to left shunt appears to decompress the right ventricleonce the right and left ventricular pressures become identical, increasing severity of pulmonic stenosis reduces the flow of blood into the pulmonary artery and increases the right to left shuntas the systolic pressures between two ventricle are identical there is little or no left to right shunt and the VSD is silent

The right to left shunt is also silent since it occurs at insignificant difference in pressure between the right ventricle and the aortathe flow from the right ventricle into the pulmonary artery occurs across the pulmonic stenosis producing an ejection systolic murmurmore severe the pulmonic stenosis, the less the flow into the pulmonary artery and the bigger the right to left shuntmore severe the pulmonic stenosis, the shorter the ejection systolic murmur and the more the cyanosis

thus the severity of cyanosis is directly proportional to the severity of pulmonic stenosis, but the intensity of the systolic murmur is inversely related to the severity of pulmonic stenosisThe VSD of TOF is always large enough to allow free exit to the right to left shuntsince the right ventricle is effectively decompressed by the VSD congestive failure never occurs in TOF.

Become symptomatic any time after birthNeonates as well as infants may develop anoxic spellsCyanosis may be present from birth or make its appearance some years after birthChild becomes more cyanosed while crying, these are called cyanotic spellsor Fallots spells.Commonest symptoms are dyspnea on exertion and exercise intolerance

Patients assume a squatting position as soon as they get dyspneic. Squatting increases the peripheral vascular resistance, which diminishes the right-to-left shunt and increases pulmonary blood flow. Anoxic spells occur predominantly after waking up or following exertionBabies who have tetralogy of Fallot may not gain weight or grow as quickly as children who have healthy hearts because they tire easily while feeding.

Cyanosis , clubbing, slightly prominent `a wave in the jugular venous pulse, normal sized heart with parasternal impulse, a systolic thrill in less than 30 % patients.Normal first sound, Single second sound (A2) heard, P2 is soft and delayed ,inaudible An ejection systolic murmur.

ECG : right axis deviation with right ventricular hypertrophyEchocardiography : the large overriding aorta, right ventricular hypertrophy and outflow obstruction can be identified

Boot shaped heart (apex is lifted up & there is a concavity in the region of pulmonary artery)Aorta is enlarged and aortic arch is present in 30% cases, RVHOligemic lung fields

Patients are prone to Infective endocarditisHemiplegia due to anoxic infarction during an anoxic spellParadoxical embolism to CNS and venous thrombosis due to sluggish circulation from polycythemia can also result in hemiplegiaBrain abscess

Management of complicationsTreatment of Anoxic spells : Knee chest position to increaseaortic resistance. The increased aortic and left ventricular pressure reduces the rush of blood through the septal hole from the right ventricle and improves blood circulation to the lungs, decreasing the right to left shunt thus decreasing the amount of deoxygenated blood entering the systemic circulation. Oxygen through a face mask to increase the amount of oxygen in the blood.

beta-blockers such as propranolol acute episodes may require rapid intervention with morphine to reduce ventilatory drive and a vasopressor such as epinephrine, phenylephrine, or norepinephrine to increase blood pressure.Correction of anemia Consider operation

Palliative treatment- Blalock-Taussig operation : connection between the right subclavian artery,and the right pulmonary artery, which increases the amount of red oxygenated blood reaching the lungs, relieving cyanosis.

Definitive treatment- Total correction: The hole in the ventricular septum is closed with a patch and the obstruction to right ventricular outflow, pulmonic stenosis, isopened. These corrections allow blood flow to the lungs for oxygenation before being pumped out into the body.

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