Cardiac physiology in a normal child is an elegant balance requiring many components to work on an interactive basis. In children with congenital or acquired heart disease, some of those parts do not function properly from the start; others develop problems with time or under duress. This chapter begins with a discussion of the syndrome of heart failure. The pathophysiology of heart failure is reviewed, followed by the diagnosis and management of left heart failure (including heart transplantation). This is followed by a more detailed discussion of the primary conditions that can lead to heart failure. We explore the diagnosis and management of various forms of cardiomyopathy, a set of intrinsic cardiac muscle disorders with often overlapping phenotypes. Finally, we present the diagnosis and management of right heart failure as a manifestation of pulmonary hypertension.
Definition and Pathophysiology
Heart failure is a clinical syndrome that develops as a final common pathway of diverse cardiac injuries. Symptoms result from an impairment in the heart's ability to adequately relax and/or contract. Historically, heart failure was defined as a pure mechanical or hemodynamic condition that resulted from an inability of the heart to provide enough cardiac output to meet the metabolic demands of the body. Therapy was directed at altering these hemodynamic derangements by increasing cardiac output, typically with medications that increased heart rate and contractility, and by decreasing metabolic demands. However, there has been a paradigm shift in the approach to heart failure in recent years. We now better understand the compensatory neurohormonal mechanisms and complex molecular signaling cascades that are activated in the setting of decreased cardiac output. These mechanisms cause adverse remodeling that perpetuates the cycle of heart failure.
Patients with heart failure have traditionally been categorized by their functional capabilities, using either the New York Heart Association (NYHA) or Ross classification schemes (Table 13-1). In recent years, the American College of Cardiology and American Heart Association have advocated the additional use of a staging system for heart failure that emphasizes the structural condition of the heart as well as the prevention, evolution, and progression of heart failure (Figure 13-1).1 It is meant to complement the NYHA classification system, which has been used to describe functional limitations rather than structural abnormalities. Stage A and B patients might best be thought of as "pre–heart failure" patients, in that they are at risk for heart failure but have not yet developed symptoms. Whereas in the following section, we will primarily address the assessment and management of stage C and D heart failure in children, the subsequent section will discuss specific cardiomyopathies, which may present at any stage of the heart failure spectrum. Referral to a cardiologist for evaluation and surveillance of a child with any stage of heart failure is recommended.
Table 13-1. Functional Classification of Heart Failure in Infants and Children