Heart failure is a complex condition with many potential causes, but
with the end result that the heart is unable to meet the metabolic
demands of the body (including growth in children). Many believe
that there must also be a component of systemic or pulmonary congestion.
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 an insult to the cardiovascular system, either acquired
or congenital. In adults, the most common insult is ischemic coronary
artery disease with resultant left ventricular dysfunction. In children,
heart failure is rarely ischemic, and the causes are quite varied
and age dependent; refer to Chapters 483 and 484 for specific lesions associated with heart
failure in children of different ages. Although infants with large
left-to-right shunts and 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 with or without
elevated ventricular filling pressures. They may have decreased
systemic blood flow as well. Severe left-sided obstructive lesions
(eg, hypoplastic left heart syndrome) often present with heart failure
in the newborn period because the left ventricle cannot adequately
eject blood to the systemic circulation. Both of these groups of
lesions are generally managed by surgery or transcatheter intervention,
but symptomatic therapy is often needed prior to surgical correction
Once the body has sensed a low cardiac output, a complex neurohormonal
cascade is activated that includes the renin-angiotensin-aldosterone
system (RAAS) and the sympathetic nervous system (Fig.
497-1). This adaptive process causes fluid retention and stimulates
release of vasopressive neurohormones such as norepinephrine in
order to maintain or increase circulating blood volume and blood
pressure. However, this cascade soon becomes maladaptive because
it increases preload and afterload in an already overstressed system.
Cellular responses are also initiated. For example, the augmentation
of beta-adrenergic activity increases intracellular calcium which
in turn increases myocardial inotropy and chronotropy. These adaptive mechanisms
also soon become maladaptive, as prolonged beta-adrenergic stimulation
of the heart leads to apoptosis and fibrosis.
Schematic representation of heart failure syndrome. Regardless
of the etiology, the pathogenesis of heart failure has similar mechanisms.
A decrease in cardiac output results in decreased end organ perfusion
and activation of a neurohormonal cascade. Stimulation of endogenous
catecholamines and activation of renin angiotensin aldosterone system
causes increasing heart rate, preload and afterload. These compensatory mechanisms
increase myocardial oxygen consumption and eventually lead to reverse
remodeling, ventricular dilatation, increased propensity for arrhythmias,
and decreased coronary reserve.
The American Heart Association and the American College of Cardiology
have divided heart failure into 4 stages: stage A: at risk for heart
failure; stage B: structural heart disease without signs or symptoms;
stage C: structural heart disease with ...