Etiology And Presentation

The heart is a pump. It may fail as a pump either from the inability to generate enough contractile force or from structural anomalies that prevent or inappropriately direct blood to the tissues. Examples of the former include myocarditis, an infection of heart muscle cells (myocytes), or a cardiomyopathy, a primary structural or metabolic abnormality of the microscopic elements of a myocyte. Examples of structural anomalies that might lead to heart failure include left-to-right shunt lesions such as ventricular septal defect; patent ductus arteriosus, and, rarely, atrial septal defect, or valvar regurgitation because of the increased volume load on the heart; and severe valvar stenosis because of the increased pressure load. When the heart is no longer able to compensate, the state of heart failure exists.

When the heart fails to adequately pump blood forward for any reason, venous congestion occurs. On the right side, the liver in particular becomes distended and engorged with blood. This leads to abdominal discomfort or vomiting initially, but in certain prolonged cases, it may lead to liver dysfunction and distension of venous collaterals, some of which may be visible under the skin (Figure 46-1). The signs of peripheral edema and jugular venous distension (Figure 46-2, left), classically seen in adults are not typically seen in infants or young children. On the left side, pulmonary venous congestion leads to fluid extravasation within the lungs, typically interstitial in infants and intraalveolar in older children and adults (Figure 46-2, right). This leads to shortness of breath, tachypnea, and dyspnea and can present on chest radiography similar to pneumonia. Indeed, in some cases, a secondary infection may develop superimposed on these wet and stiff lungs.

Figure 46-1 Liver in heart failure.

Figure 46-2 Clinical presentation of heart failure in a teenager and infant.

As the heart begins to fail in the volume of blood it can pump, the sympathetic nervous system seeks to compensate by increasing the heart rate. In these cases, an ECG may be useful in differentiating a sinus tachycardia in response to a failing heart (P-wave axis between 0 and 90 with a one-to-one relationship to the QRS complexes) versus a primary arrhythmia. If prolonged and untreated, some nonsinus heart rhythms can be the cause of heart failure. Finally, upregulation of the sympathetic nervous system may also cause vasoconstriction and diaphoresis, and the child may present as cold, pale, and diaphoretic.