Acute myocardial infarction (AMI) is rare in childhood and adolescence. Although adults acquire coronary artery disease (CAD) from lifelong deposition of atheroma and plaque, which causes coronary artery spasm and thrombosis, children usually have either an acute inflammatory condition of the coronary arteries or an anomalous origin of the left coronary artery (LCA). Intrauterine myocardial infarction (MI) also does occur, often in association with coronary artery stenosis. 
Pathophysiology and Etiology
Whatever the etiology, the final common pathway of AMI includes myocardial ischemia (resulting in hypoxia), release of inflammatory cytokines, and cell death. The terminal event is often a cardiac arrhythmia, either ventricular tachycardia deteriorating to ventricular fibrillation or extreme bradycardic arrest. The onset of the terminal event is heralded by a loss of peripheral circulation and consciousness and by cardiovascular collapse and cardiac arrest. Two leading causes of AMI in children are anomalous origin of the LCA from the pulmonary artery (ALCAPA) and Kawasaki disease.
Infants with ALCAPA develop irritability with dyspnea, tachycardia, diaphoresis, and vomiting while feeding. Irritability is secondary to anginal pain caused by a coronary artery steal phenomenon to the anomalous origin of the LCA. The flow in this vessel, which has its distribution over the left ventricular myocardium, is retrograde to the main pulmonary artery.
The diagnosis of ALCAPA is suspected in irritable anxious infants presenting with pain while feeding (a modified stress test). Electrocardiography (ECG) demonstrates classic findings of deep Q waves, peaked T waves, or ST segment changes consistent with ischemia, injury, or infarction. Confirmation of the anomaly may be obtained by means of high-quality 2-dimensional and Doppler echocardiography or cardiac catheterization with angiography. A high degree of suspicion must predominate to make this diagnosis.
Kawasaki disease is an acquired disease of unknown etiology, and it can affect all cardiac tissues (pericardium, endocardium, myocardium, valves, and conductive tissue). The pathogenetic mechanism is attributable to a high degree of immune activation. Since the introduction of intravenous (IV) gamma globulin as part of standard therapy for Kawasaki disease, the incidence of AMI due to Kawasaki disease has decreased. 
Coronary artery involvement occurs in 15-25% of children with Kawasaki disease within 1-3 weeks of onset. In patients with untreated Kawasaki disease or with residual coronary aneurysms, sudden death has resulted from AMI caused by ruptured coronary artery aneurysms or thromboses. Detrimental changes in arterial wall hemodynamics are present and persist after acute Kawasaki disease, and these changes may predispose to long-term cardiovascular events.
See Kawasaki Disease: Do You Know the Signs?, a Critical Images slideshow, to help identify the specific criteria for diagnosis.
Other, often rarer, conditions that predispose children to AMI have been described, including dextro-transposition of the great arteries (D-TGA), tetralogy of Fallot, and pulmonary atresia.
For patients undergoing the Jatene arterial switch procedure, the presence of an intramural coronary artery course in patients with D-TGA may prohibit arterial repair. Hypothetically, manipulation of the intramural coronary artery may cause damage and resultant inflammation, kinking, thrombosis, and myocardial ischemia or infarction (see Transposition of the Great Arteries).
Tetralogy of Fallot
Surgical repair of pulmonary outflow obstruction often involves patching the right ventricular outflow tract and resecting the obstructing right ventricular muscle. An estimated 2-9% of patients with tetralogy of Fallot have coronary arterial anomalies, which may affect the timing of or approach to surgical repair.
The most common anomaly (4% of patients) is the origin of the left anterior descending (LAD) coronary artery from the right coronary artery (RCA), which then courses across the pulmonary outflow tract. Inadvertent transection of this vessel yields disastrous consequences. Frequently, the conus branch of the RCA is large and supplies a significant portion of the right ventricular infundibular muscle.
Surgical techniques to avoid transection include limited incisions, varied tunneling techniques, and, perhaps, conduit placement. Cardiologists must predefine these abnormalities by means of noninvasive or invasive studies (see Tetralogy of Fallot with Pulmonary Atresia).
Pulmonary atresia with intact ventricular septum
Primitive embryonic sinusoidal connections to coronary vasculature may demonstrate severe intimal thickening, occlusion, or interruption. The RCA is most commonly affected, followed by the LAD and, less frequently, the distal extent of the circumflex coronary artery. In most patients, endocardial fibroelastosis, myocardial fibrosis, and AMI are observed (see Pulmonary Atresia with Intact Ventricular Septum).
Additional relatively uncommon predisposing conditions are as follows:
Coronary artery ostial stenosis or coronary artery kinking – These may present after arterial switch repair of D-TGA in the neonatal period or may develop years later, possibly related to aortic root dilation; they may also occur after a Ross procedure for aortic valve disease
Other abnormalities of coronary structure or course – Left main coronary artery atresia is a rare anomaly that can masquerade as dilated cardiomyopathy; coronary ostial stenoses can be seen in patients with Williams syndrome, most commonly accompanying supravalvular aortic stenosis but on rare occasions in isolation  ; infarction can present in utero in these cases  Acute MI due to fibromuscular dysplasia in a 12-year-old boy has recently been reported. 
Sudden death – Sudden death due to an aberrantly coursing left main coronary artery with its origin at the right sinus of Valsalva may present in athletes who are exercising.
Coronary insufficiency – This may develop in patients with Marfan syndrome, Takayasu arteritis, or cystic medial necrosis with aortic root dilatation, aneurysm formation, and dissection into the coronary artery
Traumatic MI – Although traumatic MI is very rare, it can occur in patients of any age; however, it is more likely to occur in ambulatory and adolescent patients
Atherosclerosis – Accelerated coronary artery atherosclerosis is known to occur in orthotopic cardiac transplant recipients on immunosuppressive therapy
Familial homozygous hypercholesterolemia
Accelerated coronary atherosclerosis due to juvenile diabetic dyslipidemia or nephrotic syndrome
Accelerated atherogenesis after treatment for childhood cancer
Sickle cell disease
Prothrombotic defects (eg, protein C deficiency and prothrombin gene mutations), especially in conjunction with other coronary anomalies 
Coronary artery spasm in adolescents
Complications of dilated or ischemic cardiomyopathy
Neonatal MI has been reported sporadically. Multiple possible etiologies have been suggested, including intrauterine myocarditis, adverse effects of maternal oxytocin administration, thromboembolism from umbilical catheters or renal vein thrombosis, coronary artery steal in association with septal hypertrophy in an infant of a diabetic mother, and antithrombin III deficiency. [11, 12]
According to the Centers for Disease Control and Prevention (CDC), annual mortality from all causes in the US pediatric population ranges from 22 deaths per 100,000 population in children aged 5-14 years to 756 deaths per 100,000 population in infants younger than 1 year. (By way of comparison, annual all-cause mortality is 90 deaths per 100,000 in persons aged 15-24 years and 2,538 deaths per 100,000 in individuals aged 65-74 years.  )
The CDC also reports that mortality from AMI is 0.2 deaths per 100,000 population in persons aged 15-24 years and fewer than 0.2 deaths per 100,000 in infants younger than 1 year. (In comparison, AMI mortality is 1.4 deaths per 100,000 population in persons aged 25-34 years and 262 deaths per 100,000 population in individuals aged 65-74 years.  )
One study used Nationwide Inpatient Sample (NIS) data from 1998-2001 to determine the incidence and outcomes of adolescent AMI and found an incidence of 157 cases per year, or 6.6 events per 1 million patient-years.  Within the subset of adolescents with AMI, the incidence was higher in individuals aged 16-18 years than in individuals aged 13-15 years.
Age- and sex-related demographics
The etiology of MI determines the age of incidence.
ALCAPA may occur as unexplained sudden death in a neonate. Coronary artery ostial stenosis may occur after repair of D-TGA in the neonatal period. In childhood, infarction may occur years after arterial switch due to kinking of the coronary arteries, possibly in association with aortic root dilation. Thrombotic coronary artery occlusion from Kawasaki disease may occur in early childhood.
Sudden death from an aberrantly coursing left main coronary artery with its origin at the right sinus of Valsalva may occur in athletes who are exercising. Coronary insufficiency may develop in patients with Marfan syndrome, Takayasu arteritis, or cystic medial necrosis with aortic root dilatation, aneurysm formation, and dissection into the coronary artery. Though very rare, traumatic MI can occur at any age; it is more likely to occur in ambulatory patients.
Accelerated atherosclerosis is known to occur in orthotopic cardiac transplant recipients on immunosuppressive therapy and can occur in early adolescence. Coronary artery spasm as a cause of acute typical chest pain with associated cardiac enzyme elevation has been increasingly recognized in adolescents with otherwise normal coronary arteries.  The incidence of substance abuse and smoking are higher in adolescents with AMI than in adolescents admitted to the hospital for other conditions. 
One study from the NIS suggests a significant male preponderance in adolescent AMI (80%). 
AMI affects a small subset of children at risk for sudden cardiac death (defined as any natural death from cardiac causes that occurs from minutes to 24 hours after the onset of symptoms  ). Early mortality can be high, depending on the cause, the speed of diagnosis, and the availability of therapeutic interventions.
In patients with Kawasaki disease, the highest risk for coronary artery events is in patients with residual giant aneurysms, particularly if both coronary artery systems are involved. A recent study looking at outcomes in 245 patients with giant aneurysms over a median of 20 years after diagnosis of Kawasaki disease reported the incidence of death was 6%, acute MI 23%, and coronary artery bypass grafts 37%. Most myocardial infarctions occurred within 2 years of diagnosis. 
Unlike adults with MI secondary to ischemic and atherogenic disease, children with MI who survive are less likely to have significant prolonged illness or disability. Some data suggest that the hospital survival for AMI in adolescents is excellent (mortality, 0.8%). 
Early diagnosis by means of echocardiography with color-flow mapping and the development of improved surgical techniques (eg, myocardial preservation) have dramatically improved the prognosis of MI in childhood.
All patients should undergo formal exercise stress testing at an appropriate age to facilitate the development of an appropriate exercise program. Long-term physical restrictions, including restrictions of participation in competitive sports, depend on whether myocardial ischemia is evident at rest or during exercise. No dietary restrictions are necessary after successful surgical revascularization with subsequent clinical improvement.
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