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Cardiomyopathy (CM) is a disease of the heart muscle, which impairs function (systolic, diastolic, or both). It is classified based on structural and functional abnormalities:
- Dilated cardiomyopathy (DCM): impairment of systolic function with ventricular dilation; predominantly involves the left ventricle (LV) and 70% of children with DCM will present in congestive heart failure (CHF)
- Hypertrophic cardiomyopathy (HCM): excessive thickening of the LV that is not secondary to load conditions, such as aortic stenosis or hypertension. Up to 20–25% of patients exhibit LV outflow tract obstruction.
- Restrictive cardiomyopathy (RCM): a rare disease characterized by normal or decreased volume of both ventricles associated with biatrial enlargement, normal LV wall thickness, impaired ventricular filling with restrictive physiology, and normal systolic function
Overall incidence of CM is 1 to 2 cases per 100,000 children per year. There is a peak incidence during the 1st year of life and a second peak in adolescence.
- DCM: 0.3 to 2.6 cases/100,000 children/year
- HCM: 0.3 to 0.5 cases/100,000 children/year
- RCM: 0.03 to 0.04 cases/100,000 children/year
- DCM: 36 cases per 100,000 people
- HCM: ~10–20 cases per 100,000 people
- RCM: least common form of CM (<5%)
- DCM: familial DCM ~20% of cases
- Autosomal dominant most common pattern. >20 genes have been identified in DCM.
- Can be associated with diseases of X-linked inheritance: Duchenne and Becker muscular dystrophy and Barth syndrome
- May also be inherited via mitochondrial DNA, with variable penetrance
- HCM: ~60% of cases are thought to be inherited; traditionally inherited in an autosomal dominant pattern with incomplete penetrance
- RCM: Idiopathic cases may have a familial occurrence and may be associated with a skeletal myopathy. An autosomal dominant form with variable penetrance has been associated with Noonan syndrome.
There are no relevant factors in prevention, although for patients undergoing chemotherapy, there are cardioprotective strategies that can be used.
- DCM: inadequate systolic function with a low cardiac index (hypoperfusion) and a high central venous pressure (systemic congestion). There can be left atrial (LA) hypertension and pulmonary hypertension (PH) from left heart dysfunction.
- HCM: Diastolic dysfunction and LV outflow tract obstruction are the most problematic and lead to LA hypertension.
- RCM: Diastolic dysfunction over time leads to LA hypertension and PH. There can also be RV dysfunction and hepatic venous congestion as a result.
- DCM: A clear etiology identified in only 30% of cases
- Of known causes, the most common is myocarditis (coxsackievirus B, adenovirus). DCM can also occur from toxin exposure (anthracyclines), ischemic coronary artery disease (anomalous left coronary artery from the pulmonary artery [ALCAPA], coronary aneurysms), and chronic tachyarrhythmias.
- Can be associated with X-linked muscular dystrophies, inborn errors of fatty acid oxidation, disorders of mitochondrial oxidative phosphorylation, nutritional deficiencies, and carnitine deficiency
- It may be familial and genetically inherited.
- Most commonly idiopathic. Many of these “idiopathic” cases have unidentified familial DCM.
- HCM: genetic etiology in up to 70% of cases; caused by myocyte hypertrophy with fibrillin disarray
- RCM: most commonly idiopathic, although known causes include the following:
- Systemic disease such as lupus erythematosus, sarcoidosis, amyloidosis, infiltrative diseases (Gaucher disease, Hurler syndrome), storage diseases (Fabry disease), carcinoid syndrome, and radiation-induced fibrosis
- Familial/inherited forms
Commonly Associated Conditions
CM is most commonly identified in otherwise healthy children but can be associated with:
- DCM: neuromuscular disorders (9%), inborn errors of metabolism (4%), or rarely with malformation syndromes (1%)
- HCM: neuromuscular disorders (8%), inborn errors of metabolism (9%), or malformation syndromes (9%)
- RCM: In some tropical regions, endomyocardial fibrosis associated with RCM is common.