Sudden unexpected death includes many causes, such as a seizure, asthma, or toxic ingestion, whereas sudden cardiac death includes just those events that directly relate to cardiovascular dysfunction. Sudden unexpected death in children occurs in 7.5 cases per 100,000 children overall with a much higher rate of 96 per 100,000 in children less than 1 year old.14 Sudden cardiac death rates range from 0.8 to 6.2 per 100,000.10,15 These numbers are approximate because there is no centralized registry of these cases. Excluding trauma, sudden cardiac death is the most common cause of sports-related death in young athletes, accounting for about 100 deaths per year in the United States.16 The greatest risk for sudden cardiac death is in patients with congenital or acquired structural cardiac disease, including those with congenital heart disease who have undergone corrective surgery. The most frequent causes of sudden cardiac death in children are listed in Table 127–3.17 Hypertrophic cardiomyopathy and congenital artery anomalies are the most common causes of sudden cardiac death in adolescents without known cardiac disease.16
Predisposing Factors for Sudden Cardiac Death in Children
||Download (.pdf) Table 127–3
Predisposing Factors for Sudden Cardiac Death in Children
|Structural/functional cardiac disease || |
Coronary artery anomalies
Dilated or restrictive cardiomyopathy
Congenital heart disease
Arrhythmogenic ventricular cardiomyopathy
|Rhythm disturbances || |
Long QT syndrome
Complete heart block
|Systemic disease ||Marfan's syndrome (aortic rupture) |
Sudden cardiac death is usually an unexpected, unwitnessed, terminal event.
Survival from an out-of-hospital cardiac arrest is very unlikely, with reported rates from 2.5% to 5%.18,19 Any surviving patients must undergo rapid stabilization, and any identified conditions must be quickly treated. In general, the principles of pediatric ALS are followed (see chapter 109). Wide QRS-complex tachydysrhythmias should not be treated with class Ia agents such as procainamide and quinidine or class III agents such as amiodarone if long QT syndrome is suspected, as these medications act by prolonging the QT interval. Class Ib drugs, such as phenytoin should be used instead; torsades should be treated with magnesium 25-50 mg/kg, max dose 2 grams (see chapter 109).
After stabilization, children who have experienced a sudden cardiac arrest should be transferred to a pediatric intensive care unit that is capable of managing cardiac disorders. A crew capable of treating cardiac arrest from any dysrhythmia must perform any transfers. In general, this should be done by a dedicated pediatric critical care transport team and in consultation with the receiving pediatric intensivist.
The majority of neurally mediated syncope is a mixed pattern of vasodepressor syncope (due to vasodilation) and cardioinhibitory syncope (due to vagal stimulation). Neurocardiogenic syncope is the most common type of syncope in children 1 and usually is preceded by a sensation of warmth, nausea, light-headedness, and a visual gray-out or tunneling of vision.5 This type of syncope frequently lasts <1 minute.4 Common precipitating factors include prolonged recumbence just before standing or prolonged standing, sight of blood or disfiguring injury (e.g., fractures or soft tissue injuries), emotional upset, mild physical trauma or pain, physical exertion, and hot or crowded conditions. Other contributing factors that are less common include hypovolemia, anemia, dehydration, and pregnancy. Breath-holding spells are a variant of this form of syncope. Medications that alter vascular tone or heart rate may contribute to the development of syncope, including β-blockers, calcium channel blockers, and diuretics. Hypovolemia can result from diuretic use in young athletes, such as wrestlers, who must comply with weight restrictions.
Diagnosing neurocardiogenic syncope in the ED can be challenging, because there is no specific diagnostic test. A history of position change, prodromal symptoms, an absence of previously noted red flags, a normal physical exam, and normal ECG fairly reliably confirm that the syncopal event is benign in nature.
Breath-holding spells are a form of neurally mediated syncope. Typical occurrence is in a 6- to 18-month-old, and an intense emotional trigger that causes crying precipitates the spell and then breath-holding during expiration.20 The child may become cyanotic or pale and lose consciousness from progressive cerebral hypoperfusion. Myoclonic activity or seizure activity may occur. The episode is usually short, requires no specific intervention, and rapidly resolves with gasping respirations and progressive loss of cyanosis or pallor. Up to 20% of children who have breath-holding spells develop neurocardiogenic syncope in later life.20
ORTHOSTATIC SYNCOPE AND POSTURAL ORTHOSTATIC TACHYCARDIA SYNDROME
Factors that predispose children to orthostatic syncope include anemia, dehydration, and use of certain medications, especially calcium channel blockers and angiotensin-converting enzyme inhibitors.5 A drop of >20 mm Hg in blood pressure with an increase in heart rate of >20 beats/min when the child changes from a supine position to a standing position is often considered diagnostic of orthostatic hypotension. Postural orthostatic tachycardia syndrome is a form of chronic orthostatic intolerance, defined by elevation in heart rate of >35 to 40 beats/min, with stable or increased blood pressure on tilt-Table testing combined with symptoms of orthostatic intolerance and sympathetic overactivation.21
Urination, defecation, coughing, and swallowing have been described as causing syncope. The pathophysiology probably is related to an exaggerated Valsalva response causing cardioinhibitory syncope. Stretching, neck extension, external neck pressure, and hair grooming also have been described as causing syncope, presumably due to carotid sinus hypersensitivity or abnormal Valsalva responses.
PEDIATRIC AUTONOMIC DISORDERS
Abnormalities in heart rate and blood pressure control can be inherited as a primary disorder. These disorders are associated with general autonomic dysfunction and present with many more symptoms than syncope. The most common is familial dysautonomia (Riley-Day syndrome). This disorder results from abnormal development of the sensory and autonomic ganglia, due to a genetic defect that inhibits neurotransmitter production. Manifestations include failure to thrive, developmental delay, temperature instability, abnormal sweating, absent lacrimation, breath-holding spells, and seizures.
Hypertrophic cardiomyopathy, also known as idiopathic hypertrophic subaortic stenosis, results in a dynamic and a fixed subvalvular obstruction (see chapter 126, "Congenital and Acquired Pediatric Heart Disease"). Exertional syncope is a common presentation, but infants may present with congestive heart failure and cyanosis. This diagnosis must be considered in any child with exertion-related syncope. A typical loud crescendo-decrescendo murmur may be heard at the left sternal border, which is accentuated by standing or Valsalva (decreased left ventricular preload). The ECG is abnormal in >75% of patients, usually with findings of left ventricular hypertrophy.16 Onset of symptoms in early childhood is associated with a greater risk of mortality—the 10-year mortality rate is 50% for children diagnosed before 14 years of age.22 Syncopal events appear to be related to myocardial ischemia and/or ventricular tachycardia, probably secondary to the long QT syndrome. Echocardiography is necessary to exclude or confirm this diagnosis and should be performed in the ED or on the inpatient ward. Patients with hypertrophic cardiomyopathy should be advised against playing competitive sports to reduce risk of sudden death. Implanted cardiac defibrillators are controversial benefit in pediatric hypertrophic cardiomyopathy and should be considered in consultation with a pediatric cardiologist.
Dilated cardiomyopathy is unusual in children but can occur by three general mechanisms: idiopathic, with congenital heart disease, or after myocarditis (see chapter 126). Syncope and death are thought to be caused by ventricular dysrhythmias or severe myocardial dysfunction.
ARRHYTHMOGENIC VENTRICULAR CARDIOMYOPATHY (FORMERLY ARRHYTHMOGENIC RIGHT VENTRICULAR DYSPLASIA)
Arrhythmogenic ventricular cardiomyopathy has a general prevalence of 1:2000; however, it is a common cause of adolescent death in certain countries such as Italy and parts of Greece.23 The disorder is more common in older adolescents and adults. Once thought to only affect the right ventricle, this has been shown to be a biventricular disease with a right-sided predominance. Patients usually present with congestive heart failure, cardiomegaly, and syncope or sudden death from a dysrhythmia. ECG abnormalities include left bundle-branch block and T-wave inversion, but some patients may have normal ECG findings. Even the echocardiogram, cardiac catheterization, and myocardial biopsy results can be nondiagnostic, which makes exclusion of this disorder by the ED physician problematic.
CONGENITAL CYANOTIC AND NONCYANOTIC HEART DISEASE
Hypercyanotic spells may progress to syncope in tetralogy of Fallot, tricuspid atresia, transposition of the great arteries, and Eisenmenger's syndrome. Children with structural heart disease are also prone to ventricular dysrhythmias and atrioventricular block (see chapter 126).
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 and is often associated with a bicuspid valve. Other associated cardiac anomalies, in particular coarctation of the aorta, also may present as syncope. Most patients with valvular disease are identified by the presence of a murmur. Exertional syncope is caused by reduced cerebral blood flow and is commonly associated with chest pain, dyspnea on exertion, and poor exercise tolerance. Mitral valve prolapse itself is probably not associated with an increased risk of sudden death, but children with the disorder do appear to have a higher frequency of syncope and arrhythmias.24 A child with mitral valve prolapse and syncope requires a more intensive diagnostic workup. Ebstein's malformation of the tricuspid valve is an uncommon disorder (see chapter 126). Sudden death in patients with this anomaly is thought to be due to the development of supraventricular or ventricular dysrhythmias.
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's 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. Physical findings include an increased ventricular impulse, a loud second heart sound, and cyanosis, which is particularly prominent in patients with Eisenmenger's syndrome. Syncope and sudden death usually are related to a dysrhythmia.
CORONARY ARTERY ABNORMALITIES
Coronary artery abnormalities can cause sudden death during exercise or exercise-induced syncope. Abnormalities of coronary artery origin include the origination of the left main artery from the right sinus of Valsalva and, less frequently, the origination of the right artery from the left sinus. In both cases, the aberrant artery often passes between the aorta and the pulmonary artery, which thus places it at risk for extrinsic compression, especially during physical exertion. The ECG in abnormal left coronary arteries shows evidence of anterolateral myocardial infarction and abnormal R-wave progression. Other coronary abnormalities include myocardial overbridging, coronary artery fistulas, coronary artery spasm, coronary ostial stenosis, coronary artery aneurysms, and stenosis from Kawasaki's disease.
NONCARDIOVASCULAR CAUSES OF SYNCOPE
Noncardiovascular causes of syncope are listed in Table 127–2.