Tetralogy of Fallot is one of the commonest cyanotic congenital heart diseases. As the name implies, there are four defects. One is ventricular septal defect, second is overriding aorta, third is pulmonary stenosis, usually right ventricular outflow tract stenosis and associated right ventricular hypertrophy. Overriding aorta with ventricular septal defect causes right to left shunt and cyanosis so that in infancy, cyanotic spells may also be there and squatting is one of the important symptoms of tetralogy of Fallot. There are several surgical options for tetralogy of Fallot and also some sequelae for these, we will see.
This is the diagrammatic representation of tetralogy of Fallot. You can see the ventricular septal defect and aortic over ride. Right to left shunt is also visible. There is right ventricular hypertrophy. Pulmonary stenosis, which is usually right ventricular outflow tract stenosis. Sometimes there could be associated annular stenosis as well and valvar sometimes. So this is tetralogy of Fallot. The right to left shunt causes cyanosis, clubbing and other features of tetralogy of Fallot. Straight forward surgical approach should be repair in infancy itself, when a patch is used to close the ventricular septal defect. Right ventricular outflow tract is resected so that the narrowing is removed. But sometimes, when there is annular stenosis, you may have to widen the right ventricular outflow tract, with a trans-annular patch. This will almost invariably result in severe pulmonary regurgitation. Severe pulmonary regurgitation initially will be tolerated, but in the long run, it can cause problems and some have resorted to pulmonary valve replacement later on. And right ventricular hypertrophy and the abnormal architecture of the right ventricle, can predispose to late arrhythmias and sudden cardiac death in repaired tetralogy of Fallot. That is why they need follow up for arrhythmias. Post operative arrhythmias, long term arrhythmias, an important cause of sudden cardiac death in repaired tetralogy of Fallot. When there is severe pulmonary regurgitation after using a trans-annular patch, for tetralogy of Fallot repair, that is also another reason for increased chance for arrhythmias, ventricular arrhythmias after repair of tetralogy of Fallot. The risk of sudden cardiac death in operated tetralogy of Fallot is 25 to 100 fold than the general population and it can occur decades after correction. The risk is related to QRS duration more than 180 milliseconds. The QRS widening is related to pulmonary regurgitation, right ventricular dilatation and conduction defect. Atrial arrhythmias are also common after TOF repair. Hemodynamic effects of pulmonary regurgitation include chronic right ventricular volume overload, right ventricular dysfunction and exercise intolerance. Pulmonary valve replacement can decrease QRS duration, and stabilize right ventricular function. Though the timing is unclear, earlier would be better than later. Right ventricular function can be evaluated by echo or magnetic resonance imaging. Those who had pulmonary valve atresia or anomalous left anterior descending coronary artery may have had prosthetic or homograft conduits with or without a valve placed between the right ventricle and pulmonary artery. Endothelial overgrowth can occur within the conduits and cause obstruction of the right ventricular outflow tract. This can be treated with balloon dilatation or surgical replacement of the conduit.
When an immediate intracardiac repair is not feasible, in certain cases of tetralogy of Fallot, especially due to poor development of the pulmonary arteries, then palliative procedures are done. Blalock-Taussig shunt or classical Blalock-Taussig shunt, one of the oldest palliative procedures, seldom done now a days, is division of subclavian and anastomosis to pulmonary artery. This will improve the pulmonary blood flow and relieve cyanosis. But this has some problems. One, the flow may be increased in the long run, leading to pulmonary hypertension and pulmonary vascular disease. Second, you are removing the blood supply to the arm. This could lead to exercise related symptoms in the arm, and sometimes, also subclavian steal syndrome, as there could be retrograde flow into the exercising arm, from the cerebral circulation. And, usually this done, Blalock-Taussig shunt, classic shunt, opposite to the side of the aortic arch. That is to prevent kinking of the subclavian when it is brought down to anastomose with the pulmonary artery. Those who have undergone Blalock-Taussig shunt, may develop pulmonary artery stenosis sometimes.between the pulmonary artery and the subclavian artery.
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