HYPERTROPHIC CARDIOMYOPATHY Also known as idiopathic hypertrophic subaortic stenosis, this disease is both a dynamic and a fixed subvalvular obstruction. Exertional syncope is a common presentation, but infants may present with congestive heart failure and cyanosis. Any child with exertional related syncope must have this diagnosis considered. Onset of symptoms in early childhood is associated with a greater risk of mortality; the 10-year mortality is 50 percent for children diagnosed by 14 years of age.22 Syncopal events appear to be related to myocardial ischemia and/or ventricular tachycardia, probably as a LQTS. An echocardiogram is necessary to exclude or confirm this diagnosis and should be done in the emergency department or on the inpatient ward. Most authors recommend implantable cardiac defibrillators in children with hypertrophic cardiomyopathy.
DILATED CARDIOMYOPATHY This disorder is unusual in children but can occur by three general mechanisms: idiopathic, with congenital heart disease, or after myocarditis. Syncope and death are thought to be caused by ventricular dysrhythmias or severe myocardial dysfunction.
ARRHYTHMOGENIC RIGHT VENTRICULAR DYSPLASIA This disorder is rare in the United States but is a common cause of adolescent death in Italy. Presentation is more common in older adolescents or adults.14 Patients usually present with congestive heart failure, cardiomegaly, and syncope or sudden death from an dysrhythmia. ECG abnormalities include left bundle branch block and T-wave inversion, but some patients may have a normal ECG. 14
CONGENITAL CYANOTIC AND NONCYANOTIC HEART DISEASE Hypercyanotic spells may progress to syncope in tetralogy of Fallot, tricuspid atresia, TGA, and Eisenmenger syndrome. Children with structural heart disease are also prone to ventricular dysrhythmias and AV block.
VALVULAR DISEASES Several valvular lesions are associated with syncope and sudden death. In general, the degree of valve dysfunction correlates with the risk of sudden death. Aortic stenosis is usually due to a congenital defect, often associated with a bicuspid valve, although unicommissural or severely dysplastic valves also occur. Other associated cardiac anomalies, particularly coarctation of the aorta, also occur. 23 Most patients are identified by the presence of a murmur. Exertional syncope is due to reduced cerebral blood flow and is commonly associated with chest pain, dyspnea on exertion, and poor exercise tolerance. 23 Mitral valve prolapse (MVP) is probably not by itself associated with an increased risk of sudden death. 24 A child with MVP and syncope requires a more intensive diagnostic workup. Adults with MVP and significant mitral regurgitation have more frequent dysrhythmias, but this has not been shown in children. Ebstein malformation of the tricuspid valve is an uncommon disorder. Sudden death is thought to be due to the development of supraventricular or ventricular dysrhythmias. 25
PULMONARY HYPERTENSION Primary pulmonary hypertension (without structural heart disease) is uncommon but can present in adolescence. It is often associated with dyspnea on exertion, shortness of breath, exercise intolerance, and syncope. Eisenmenger syndrome is acquired pulmonary hypertension due to a cardiac shunt. High blood flow to the pulmonary circulation from a left-to-right shunt leads to a reactive increase in pulmonary resistance. After months to years, the development of pulmonary hypertension causes the shunt to reverse to a right-to-left shunt and cyanosis becomes apparent. One-half of patients with pulmonary hypertension develop syncope.14 Physical findings include an increased ventricular impulse, a loud second heart sound, and cyanosis, which is particularly prominent in patients with Eisenmenger syndrome. Syncope and sudden death in these patients are usually related to an dysrhythmia.
CORONARY ARTERY ABNORMALITIES Many of these patients present with sudden death often during exercise or with a prior history of exercise-induced syncope.26 Abnormalities of coronary artery origin include the left main artery arising from the right sinus of Valsalva or, less frequently, the right artery arising from the left sinus. In both cases, the aberrant artery often passes between the aorta and pulmonary artery, thus placing it at risk for extrinsic compression, especially during physical exertion. Other abnormalities include myocardial overbridging, coronary artery fistulae, coronary artery spasm, and coronary artery aneurysms and stenosis from Kawasaki disease.
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