This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'The commonest type of song. cyanotic heart disease is - \nSelect and explain. \nA. ASD, B. VSD, C. TOF, D. PDA', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Tetralogy of fallot is the commonest cyanotic congenital heart disease.\nCyanotic Congenitial heart diseases \n\nCyanotic CHDs are Right to Left shunts.\nThese are further divided into : -\n\n1) Cyanotic CHD, with decreased pulmonary blood flow.\n\nThis group includes → TOF, Pulmonary atresia with intact septum, tricuspid atresia, total anomalous pulmonary venous return with obstruction.\nThese lesions have following components : -\n\na) Obstruction to pulmonary blood flow at tricuspid right ventricular or pulmonary valve level.\nb) A pathway by which systemic venous blood enters the systemic circulation via a patent foramen ovale or ASD or VSD.\n\nThe degree of cyanosis depends on the degree of obstruction to pulmonary blood flow : -\n\n\nMild obstruction → Cyanosis is precipitaed by stress, but may be absent at rest.\nSevere obstruction → Pulmonary blood flow is dependent on patency of the ductus arteriosus. When the ductus closes (10-21 days), the neonate experience profound hypoxemia, cyanosis and shock.\n\n2) Cyanotic CBD with increased pulmonary blood flow.\n\nThis group of lesions is not associated with obstruction to pulmonary blood flow.\nCyanosis caused by any of the following mechanisms.\n\n\n\nAbnormal ventricular-arterial connection (e.g., Transposition of great vessels) → In this, aorta arises from rt ventricle, So that systemic venous blood returning to the right atrium is pumped directly back to the body, and oxygenated blood returning from lung is pumped back into the lungs.\nTotal mixing of systemic venous and pulmonary venous blood (e.g., total anomalous pulmonary venous return, truncus arteriosus, a common atrium or ventricle) → Deoxygenated systemic venous blood and oxygenated pulmonary venous blood mix completely in the heart and, as a result, oxygen saturation is equal in the pulmonary artery and aorta. lf pulmonary blood flow is not obstructed, these infants have a combination of Cyanosis and heart failure. In Contrast, if pulmonary stenosis is present, these infants have cyanosis alone.', 'role': 'assistant'}]