Tetralogy Of Fallot

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  • 1. TETRALOGY OF FALLOT: Definition: Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect after infancy. It is characterized by a large VSD, an aorta that overrides ventricle, right ventricular hypertrophy and obstruction of the right ventricular outflow tract. Etienne-Louis Arthur Fallot a French physician described it accurately in 1888. Fallot’s pentology means Tetralogy of Fallot plus persistent foramen Ovale or atrial septal defect. Fallot’s Trilogy means atrial septal defect plus pulmonary stenosis with intact interventricular septum. Pathophysiology: The right ventricular outflow tract obstruction is the most important component of Fallot’s tetralogy. It is most often sub-valvular in location. But it can also be valvular or supra valvular or a combination of these. The ventricular septal defect is usually large and causes right to left shunting of blood in this situation of elevated right ventricular pressure. The peri-membraneous location of the ventricular septal defect is responsible for the over-riding of aorta. The obstruction to the right ventricular outflow leads to the development of right ventricular hypertrophy. The right ventricular outflow obstruction also results in reduction to the pulmonary blood flow. Arterial desaturation develops because of the right to left shunting of blood between the ventricles and hence patient develops cyanosis. The tetralogy of Fallot generally results in low oxygenation of blood due to mixing of oxygenated and deoxygenated blood in the left ventricle and preferential flow of blood from the ventricles to the aorta because of obstruction to flow through the pulmonary valve. Thus a mixture of blood from right and left ventricles enters the aorta. Symptoms: Tetralogy of Fallot seldom presents with cyanosis at birth. Symptoms usually appear at the end of first year of life. Some children with mild Fallot’s tetralogy may never develop cyanosis because the pulmonary stenosis may be very mild, that the pulmonary blood flow is not compromised and any significance admixture of blood occurs in the ventricular levels. These cases are called acyanotic Fallot. The infants usually do not manifest cyanosis. They develop cyanosis only when they are feeding or crying. This is because the sub-valvular obstruction to the right ventricular outflow is dynamic in nature. It increases with adrenergic stimulation and the flow across the valve decreases. This makes the child increasingly cyanosed, breathless and even aponoeic. Some times loss of consciousness or convulsions may occur. These are called Fallot’s spells. The age, at which symptoms appear, depends upon the severity of right ventricular obstruction. The main symptoms are cyanosis, cyanotic spells and squatting and exertional dyspnoea. Slight bluish discoloration of the tongue and
  • 2. lips may be evident on close observation of the child, in presence of large ventricular shunting of blood. Cyanotic spells usually occur after the age of three to six months, when the child becomes increasingly active. It is characterized by sudden onset of breathlessness, restlessness and increasing bluish discoloration of the skin and mucous membranes. At the peak of the symptoms the child may loose consciousness and develop convulsions. Sometimes the cyanotic spells can be even fatal. Squatting is the posture adopted by older children with Tetralogy of Fallot, who have learned from experience that, it will relieve them from cyanosis. The child stops playing and sits on ground in a knee close to cheat position. This produces significant reduction in symptoms of breathless and cyanosis at least temporarily. After infancy the children become more and more cyanotic as the right ventricular pressure increases and the right to left shunt also. These children do not manifest much dyspnoea, but cyanosis is more apparent. These children more often assume the squatting posture to get relief from the cyanosis. Signs: The pulse is usually is not altered nor is the blood pressure. The jugular venous pressure also is not elevated initially. Characteristically the child has a silent precordium. The apex beat is not prominent. Depending on the degree of right ventricular hypertrophy there may be left parasternal heave