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Sudden death in childhood is rare. About 10% of paediatric deaths after the first year of life are sudden and population based studies put the individual age related risk at around 1:20 000 to 1:50 000 per year. (1-4)(wi-3) About ha if of these deaths are related to a previously known abnormality, the most common being epilepsy, asthma, and cardiovascular abnormalities. Another third are attributed to an abnormality discovered at necropsy, usually either an infection or a cardiovascular abnormality. At least one sudden death in six remains unexplained, but this is almost certainly an underestimate as some deaths attributed by the coroner's pathologist to epilepsy or respiratory infection are probably more accurately described as being unexplained by findings at necropsy. (4 w4)
MECHANISMS OF SUDDEN DEATH
Although all deaths result in asystole, not all sudden deaths are caused by arrhythmias. The precise mechanism of sudden death depends upon the cause. One report of terminal electrical activity in paediatric patients dying in hospital documented bradycardic arrest in 88% of neonates, 67% of infants, and 64% of children. (5) Ventricular tachycardia or fibrillation was more likely in those with heart disease and in older children. The term "sudden death" should not be confused with non-fatal cardiac arrest. (w5)
Sudden cardiac death in infancy
Sudden death in infancy is usually caused either by infection or by sudden infant death syndrome. A few neonatal or infant deaths are caused by unrecognised congenital cardiovascular malformations, particularly duct dependent abnormalities or obstructive left heart malformations. (w6) Primary arrhythmias are rare causes of death in infancy but fatal ventricular arrhythmias are described. (6) Complete atrioventricular block is usually recognised in utero or soon after birth but may cause death if unrecognised or untreated. (w7)
Sudden death in children with postoperative congenital heart disease
In the 1960s and 1970s sudden cardiac death most often occurred in children with irreversible pulmonary vascular disease associated with unoperated congenital heart disease or in children with unoperated aortic valve stenosis. (w8 29) In recent years surgical repair has been performed earlier and more effectively so that those most at risk of sudden death now are children with repaired heart disease. In a population based study of late postoperative sudden death, Silka and colleagues identified an average risk of 0.9 per 1000 patient-years follow up for the most common surgically repaired malformations. (7) Those patients with a risk above the average had aortic valve stenosis, transposition of the great arteries, tetralogy of Fallot or coarctation of the aorta. Death was attributed to "arrhythmia" in the majority, based on the history, but in only a few was an arrhythmia identified in life.
Sudden death in adults with congenital heart disease
Among patients in an adult congenital heart follow up clinic in Toronto, not all of whom had undergone surgery, the reported sudden death rate was 5.3 per 1000 patient-years. (8) The most common abnormalities in those who died suddenly were Eisenmenger's syndrome, tetralogy of Fallot, and transposition of the great arteries, but the risk for individual diagnoses could not be assessed for lack of a denominator. In a more recent report from the same unit, 8% of adult patients died during follow up--65% of deaths were cardiovascular and 26% were sudden. (w10) Although numbers for individual diagnoses were small, the highest proportion of deaths were sudden in patients with coarctation of the aorta, Ebstein's anomaly, and congenitally corrected transposition of the great arteries. The highest number of sudden deaths in the clinic population occurred in patients who had undergone repair of tetralogy of Failot.
Sudden death after repair of tetralogy of Fallot
Of the various problems encountered late after surgical repair of tetralogy of Fallot, sudden death is the most difficult to predict. It usually occurs many years after operation (w11) and thus affects young adults more than children, with an average risk of 1.4 per 1000 patient years, or about 1 in 700 per year. (9) Many risk factors for sudden death have been identified retrospectively, but prospectively, even in combination, they are not useful in predicting risk. (10 w12 w13) Although ventricular tachycardia or fibrillation is thought to be the most common mechanism of sudden death, more minor ventricular arrhythmias are so common as to be unhelpful in predicting risk. An important recent "pseudo-prospective" multicentre study involving six centres in the UK, USA, Canada, and Japan retrospectively identified 793 patients alive in 1985 and "followed" their progress for the next 10 years, yielding more than 7500 patient-years follow up. (11) Thirty three patients …