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Heart failure is a complex condition with many potential causes, but with the end result of the inability of the heart to keep up with the demands of the body. Many feel that there must also be a component of congestion (either systemic or pulmonary) to the condition of heart failure. However, some patients with heart failure may have no significant congestion at rest, but only develop congestion with exertion or other forms of increased oxygen demand. Heart failure is generally precipitated by some type of insult to the cardiovascular system, either acquired or congenital. In adults, the most common form of insult is ischemic coronary artery disease with resultant abnormal left ventricular function. In children, the etiologies of heart failure are rarely ischemic and are quite varied and age-dependent. Please refer to Chapters 478 and 479 of this book for specific lesions associated with heart failure in children of different ages. Although infants with large left-to-right shunts with pulmonary overcirculation are commonly referred to as being in heart failure, their ventricular performance is usually normal, and their “heart failure” is usually a manifestation of pulmonary overcirculation and elevated ventricular filling pressures secondary to this. There can be a component of decreased systemic cardiac output as well. In addition, severe left-sided obstructive lesions (eg, hypoplastic left heart syndrome, coarctation, or critical aortic stenosis) often present with heart failure in the newborn period due to the inability of the left ventricle to adequately eject blood to the systemic circulation. Both of these lesions are generally quite well managed with surgical or transcatheter intervention and will not be discussed in this section. Rather, this chapter will focus on the type of pediatric heart failure that presents acutely (either due to systemic ventricular dysfunction or after cardiac surgery) or develops chronically, primarily as a result of decreased systemic ventricular performance.
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The condition of heart failure is well described in the adult and, to a lesser extent, in the child. Once the body has sensed a condition of low cardiac output, a complex neurohormonal cascade is activated that includes the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (Fig. 491-1). This adaptive process results in fluid retention and stimulation of vasopressive neurohormones such as norepinephrine, with the intention of maintaining or increasing circulating blood volume and blood pressure. However, in the setting of decreased ventricular function, this adaptive function soon becomes maladaptive in that it increases preload and afterload in an already overstressed system. At a cellular level, an increase in β-adrenergic stimulation results in increased intracellular calcium in order to increase inotropy and chronotropy. However, these adaptive mechanisms also soon become maladaptive.
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