Sick neonates without cardiac anatomic anomaly often develop symptoms of cardiac and myocardial dysfunction. Systolic and/or diastolic dysfunction most often occur secondary to another abnormality such as sepsis or hypothermia, but occasionally from disorders fundamentally involving myocyte biochemistry. Cardiomyopathy is abnormal myocardial cellular function or structure that occurs with
many abnormalities and disorders (see Tables 33-16 and 33-17). Myocardial dysfunction may be grouped by clinical and echocardiographic determination of the cardiovascular pathophysiology, without regard to etiology, as dilated, hypertrophic, and restrictive cardiomyopathy. The nature of appropriate supportive cardiac treatment depends on this cardiovascular physiologic classification. However, the outcome of supportive therapies alone is limited. Additional improvement in outcome may result from determining causation and directed treatment based on etiology.

Dilated cardiomyopathies are characterized by diminished cardiac contractility, with ventricular enlargement, abnormal diastolic function, and congestive heart failure. Neonates with dilated cardiomyopathy more frequently have an identifiable cause than is currently achievable in older children and adults (see Table 33-16). These include identifiable infection (e.g., bacterial or viral sepsis, Coxsackie or adenovirus myocarditis, toxoplasmosis), ischemia (e.g.,
birth asphyxia, anomalous left coronary artery origin), hemodynamic work overload (e.g., incessant tachyarrhythmia) and electrolyte or metabolic imbalance (e.g., hypothermia, polycythemia, hypoglycemia, hypocalcemia). Increasingly infants are being recognized with primary biochemical disorders of energy production and metabolism that result in isolated cardiomyopathy or generalized myopathy and encephalopathy (33,34 and 35). These infants often have significant deterioration with stress, including that with birth. Caution should be used in attributing permanent or temporary cardiac dysfunction and encephalopathy entirely to “birth asphyxia” in a baby with low Apgar scores without identifiable perinatal cause for asphyxia. Additionally, myocardial diseases that more commonly
present in older children, such as those associated with neuromuscular disorders; sometimes have unusually early presentations in infancy.

Although the etiologies are diverse, in most dilated cardiomyopathies the clinical course, pathophysiology, and some molecular mechanisms are similar. Myocyte damage, from infection, cytokines, toxic metabolite, or energy deprivation from metabolic block or ischemia, results in myocardial injury. This results in a sequence of molecular and cellular changes with myocardial dysfunction, stunning, apoptosis, necrosis, and interstitial fibrosis, leading to impaired systolic contractility and diastolic compliance. Ventricular enlargement, because of Frank-Starling phenomenon, and tachycardia partially compensate for diminished systolic shortening fraction and support resting cardiac output, but use up reserve in pump function. The impairment in diastolic compliance results in generalized edema and in pulmonary venous engorgement with tachypnea. If cardiac function worsens, resting cardiac output diminishes, and multi-system dysfunction results.