The term “heart failure” (HF) describes a state of cardiac dysfunction whereby the heart fails to generate sufficient forward output to meet the body’s metabolic demands, or meets those needs only in the setting of abnormally elevated filling pressures.¹ The clinical appearance of a patient in HF depends on how well cardiovascular adaptations maintain cardiac output in the face of varying physiologic demands. With progressive disease, these physiologic responses reach a threshold limit after which they fail to prevent fluid from accumulating in body organs or to preserve adequate tissue perfusion, and a state of circulatory dysfunction is reached known as decompensated congestive heart failure.

In the United States, the incidence of pediatric heart failure has been estimated as high as 12,000 to 35,000 per year.^2–4 Among children who develop cardiac failure, 70% to 80% do so in the first year of life, most commonly from congenital heart disease^2,5,6; of the remainder who develop cardiac failure after 1 year of age, half are related to congenital anomalies and the other half due to acquired conditions.⁶ In general, outcomes of heart failure in children depend on the underlying cause. Overall mortality in pediatric heart failure is about 7%,^3,7 with mortality associated with congenital heart disease declining significantly over the past two decades. However, up to 40% of children with cardiomyopathy progress to transplant or death.⁸

The most likely etiology of acute heart failure is age-dependent in children, and the timing of onset can provide important clues to underlying cause (Table 41-1). In the younger infant, heart failure is most likely related to structural heart disease including shunting and valvar lesions, yet inborn errors of metabolism, neuromuscular disease, arrhythmia or respiratory illnesses, anemia, and infection must be considered. In an older child, the etiology may relate to primary cardiomyopathy (dilated, hypertrophic, restrictive, non-compaction, arrhythmogenic right ventricular cardiomyopathy) or unrepaired structural defects as well as secondary cardiomyopathy related to metabolic, infectious, genetic, and/or environmental (toxins, chemotherapy) origins.^2,4,9

Acute heart failure syndromes are triggered by derangements in any one or more of five hemodynamic factors contributing to cardiac output: preload, afterload, contractility (systolic function), heart rate, and diastolic function.

1. 
   

   Preload (venous return to the right or left heart) represents ventricular filling volumes and thus filling pressures at end diastole, and is increased in the setting of left-to-right shunts or in high-output states such as anemia, sepsis, or overtransfusion. In the setting of systolic dysfunction, increased preload will result in ventricular dilation and can raise cardiac output. An emergency clinician will often seek to gauge volume status to predict response to IV fluids. An increase in blood volume (or preload) with IVF may result either in improved cardiac output or may overwhelm the ventricle’s ability to accept or reject that volume, leading to right- or left-sided backflow, congestion, and clinical deterioration.

   
   
2. 
   

   Afterload (the myocardial wall stress generated by the ventricles at end-systole) depends on the resistance or pressure load the myocytes face upon ejection of blood. Afterload has an important role in ventricular outlet obstruction or pulmonary or systemic hypertension. In the setting of increasing afterload, myocardial oxygen demand and cardiac work will rise, and the ventricle will thicken to keep pace with pressure load, resulting in greater energy expenditure.

   
   
3. 
   

   Contractility (force of ventricular contraction) is altered in infectious myocarditis, multiple forms of cardiomyopathy, and vasculitis such as Kawasaki disease, arrhythmia, or hypothyroidism. Contractility is dynamic and may be augmented in the setting of changing afterload. In other words, contractility is load-dependent and may be increased to overcome rising afterload until a point when ejection capacity no longer keeps pace with heart rate. It is important to note that the ventricle with impaired systolic function or contractility is highly sensitive to increases in afterload, and even small increases may result in a significant drop in cardiac output.

   
   
4. 
   

   Heart rate can either be too slow, resulting in inadequate output, or too fast. Increases in heart rate will improve stroke volume to a point until diastolic filling time is insufficient to fully fill ventricles, with consequent drop in cardiac output.

   
   
5. 
   

   Diastolic function refers to ventricular relaxation (an active, energy-dependent process after contraction) as well as ventricular compliance (a passive process akin to the stiffness or thickness of the ventricular walls). Diastolic function is impaired in ischemic heart disease and restrictive cardiomyopathy, among other conditions.^4,9 In the setting of diastolic dysfunction, elevated venous pressures are required to achieve ventricular filling, without which cardiac output may drop despite normal systolic function.

The clinical progression of heart failure can be described as the decremental ability of neuro-hormonal adaptations to compensate for derangements in any of these factors impacting cardiac output. In the setting of cardiac damage, deficiencies in oxygen and nutrient delivery trigger up-regulation of the renin–angiotensin–aldosterone system leading to increased sodium and water retention, which in turn expands blood volume and increases preload (myocardial stretch). The sympathetic nervous system is also stimulated to increase heart rate and raise vascular tone and blood pressure (afterload). The combined effect of these adaptations—aimed at increasing ventricular volumes (preload), tachycardia, and hypertension (afterload)—will serve to maintain delivery of blood flow to the systemic vascular beds. Mild initial reduction in heart function can be normalized to maintain cardiac output with mechanical adaptations: the response of the heart to increased systemic vascular resistance (pressure overload in systole) is concentric myocardial thickening, while the response to increased filling pressure (volume overload in diastole) is chamber dilation. With myocardial stretch and chamber dilation, the heart is able to augment its force of contraction and therefore improve stroke volume. This phenomenon is known as the Frank–Starling mechanism. However, each adaptive mechanism has an upper threshold limit after which normal stroke volume is no longer sustainable. Often in the setting of an acute insult (such as an infectious illness), the threshold limits of compensatory mechanisms are surpassed, ultimately triggering circulatory failure, end-organ hypoperfusion, acidosis, shock, and even death.^1,2,9

In advanced or chronic heart failure, myocardial cells die from energy starvation, from cytotoxic mechanisms leading to necrosis, or from the acceleration of apoptosis. This loss of myocytes leads to cardiac dilation, increased afterload, wall tension, and further systolic dysfunction.^10,11

The hemodynamic derangements in heart failure syndromes will manifest in a continuum of disordered systolic or disordered diastolic function in which filling pressures are either elevated or normal (congestion is present or absent, lungs are wet or dry) and systemic output is adequate or limited (tissue perfusion is adequate or inadequate, warm or cold on exam).¹² This is represented in the following table:

• 
  

  Warm and Dry: Earliest stage of heart failure. Normal cardiac output. Represents asymptomatic ventricular dysfunction while adaptations maintain normal stroke volume, with normal filling pressures and adequate perfusion. The primary focus is prevention of disease progression.

  
  
• 
  

  Warm and Wet: Elevated filling pressures and pulmonary edema with adequate perfusion. Most common stage noted on initial ED presentation. Congestive symptoms depend upon whether the right heart or left heart is primarily affected. Left-sided diastolic dysfunction results in elevated left atrial (LA) pressure, with retrograde elevation of pulmonary venous hydrostatic pressure, capillary leak, and pulmonary edema, marked by the constellation of heart failure symptoms including shortness of breath, increased metabolic demands, exercise intolerance, and poor weight gain. Respiratory symptoms may closely resemble bronchiolitis or asthma. Right-sided diastolic dysfunction drives elevated right atrial (RA) pressure, manifesting with jugular venous distention, hepatomegaly, and peripheral dependent edema.

  
  
• 
  

  Cold and Dry: Normal filling pressures with poor perfusion, requiring aggressive treatment. “Cold” symptoms by organ system include muscles (exercise intolerance), skin (pallor, cool distal extremities due to vasoconstriction and shunting of blood away from the periphery toward vital organs, sweating during feeding due to sympathetic stimulation), intestines (nausea, abdominal pain, anorexia), kidneys (decreased urine production), brain (acute: syncope, confusion, agitation, fatigue; chronic: somnolence, coma), heart (ischemia, death). In children, poor perfusion to the intestine may lead to anorexia, nausea, or vomiting, mimicking a common gastroenteritis illness or even sepsis.

  
  
• 
  

  Cold and Wet: Characterized by elevated filling pressures and poor perfusion. Most dire stage, requiring intensive care management.¹²

OVERLAP OF DISORDERED SYSTOLIC AND/OR DIASTOLIC DYSFUNCTION

At the onset of disease, many lesions have a disproportionate impact on any one of these factors affecting cardiac output: preload, afterload, heart rate, contractility, and ventricular compliance—resulting primarily in either systolic or diastolic dysfunction. However, most lesions will overlap over time, with primary systolic function leading to diastolic dysfunction, and vice versa. For example, primary low output lesions with systolic dysfunction, such as systemic outflow tract obstruction lesions (aortic stenosis) or impaired ventricular contractility states (dilated cardiomyopathy), will result in advanced disease as low output lesions; however, higher filling pressures ultimately result in congestion. Lesions with primarily diastolic dysfunction and congestive symptoms at the onset—for example, left-sided obstruction lesions (mitral valve stenosis) or restrictive cardiomyopathy—in the clinical context of low circulating volume, such as diarrhea, will be noted in combination with low systemic flow and hypoperfusion symptoms.

PRIMARY SYSTOLIC DYSFUNCTION/LOW-OUTPUT LESIONS

1. 
   

   Impaired contractility (e.g., myocarditis, dilated cardiomyopathy, incessant arrhythmia, ischemia, sepsis): Injury to the heart muscle reduces ventricular contractility, leading to impaired ejection of blood from the ventricle with symptoms of pump failure. In children, HF as a result of myocardial ischemia/infarction is uncommon. Infants born with an anomalous left coronary artery arising from the pulmonary artery (ALCAPA) usually present with symptoms and signs of myocardial ischemia/infarction, damaging the left-sided myocardium. Coronary vasculitis associated with Kawasaki disease may rarely present with myocardial ischemia and left ventricular dysfunction.

   
   
2. 
   

   Left heart outlet obstruction (e.g., aortic stenosis, hypertrophic obstructive cardiomyopathy): Left-sided obstruction may reduce the ejection of blood from the left ventricle, leading to coronary or peripheral ischemia during exertion, and dysrhythmias. The pressure load (afterload) faced by the left heart will lead to left heart concentric hypertrophy, to progressive difficulty filling the ventricle over time, resulting in a drop in stroke volume over time and hypoperfusion. Some lesions, such as critical aortic stenosis or hypoplastic left heart syndrome, may manifest with signs of heart failure and shock in the very early newborn period (first 3 days of life), unless the ductus arteriosus (DA) is open to deliver deoxygenated blood from the pulmonary artery to the descending aorta to maintain cardiac output. A narrowing or closing DA, failing to provide sufficient systemic output, will quickly lead to hypoperfusion, metabolic acidosis, and circulatory collapse.

   
   
3. 
   

   Right heart outlet obstruction (e.g., Tetralogy of Fallot, pulmonary hypertension): If there is a right-to-left shunt in the setting of right-sided outlet obstruction, the patient is cyanotic at presentation. If there is no right-to-left shunt (or it is small and inadequate), the LV cannot be filled, leading to hypotension and shock.

   
   
4. 
   

   Incessant tachycardia (e.g., prolonged supraventricular tachycardia, thyrotoxicosis, intoxications): At very rapid heart rates, there is reduced time for ventricular filling during diastole and the cardiac output drops.

   
   
5. 
   

   Chronic valvar regurgitation lesions (e.g., aortic or mitral regurgitation): In chronic aortic regurgitation, increased ventricular filling volume (or preload) will lead to adaptive left ventricular and left atrial enlargement, with a resultant initial increase in ejection fraction and stroke volume (from Frank–Starling mechanism). However, with time the ventricle may ultimately fail, leading to a deterioration in ventricular systolic function, congestion, and a low output state.

DISORDERED DIASTOLE RESULTING IN CONGESTION

Diastolic dysfunction due to impaired myofibril relaxation or ventricular stiffness leads to difficulty filling the ventricle with progressive concentric remodeling (thickening), and ventricular filling may ultimately be incomplete.¹³ Diastolic dysfunction may occur alone as in restrictive or ischemic cardiomyopathy, or in combination with systolic heart failure.

1. 
   

   Left-sided diastolic dysfunction results in elevated LA pressure, with retrograde elevation of pulmonary venous hydrostatic pressure, capillary leak, and pulmonary edema, marked by the constellation of heart failure symptoms including shortness of breath, increased metabolic demands, exercise intolerance, and poor weight gain. Respiratory symptoms may closely resemble bronchiolitis or asthma.

   
   
2. 
   

   Impaired ventricular filling lesions (e.g., mitral valve stenosis or hypertrophic obstructive cardiomyopathy) lead to a similar retrograde rise in left atrial pressure and pulmonary venous congestion, worsening with increases in heart rate or afterload faced by the systemic ventricle.

   
   
3. 
   

   Right-sided diastolic dysfunction drives elevated RA pressure, manifesting with jugular venous distention, hepatomegaly, and peripheral dependent edema. In the presence of an atrial level shunt, blood will shunt right to left due to downstream impedance, and leads to cyanosis at presentation.

   
   
4. 
   

   Of note, patients with chronic HF often develop secondary pulmonary hypertension, which can contribute to dyspnea as pulmonary pressures rise with exertion. If a shunt at either the ventricular level (ventricular septal defect [VSD]) or arterial level (pulmonary ductus arteriosis [PDA]) in a patient with pulmonary hypertension is present, right-to-left shunting will preserve cardiac output, but at the expense of cyanosis. This phenomenon as a chronic condition is called Eisenmenger syndrome. If there is no right-to-left shunting, right-sided HF can occur from pressure overload.

PRIMARY CONGESTION LESIONS

1. 
   

   Impaired left ventricular filling lesions (e.g., pulmonary vein stenosis, cor tri triatum, mitral valve stenosis): Lesions that result in elevated left atrial pressure venous pressure or “back pressure” on the lungs will produce pulmonary venous hypertension and eventually pulmonary edema due to elevated hydrostatic pressure and capillary leak. Associated symptoms include respiratory distress, increased metabolic demands, exercise intolerance, and poor weight gain.

   
   
2. 
   

   Left-to-right shunt, or “pulmonary overcirculation” (e.g., ventricular septal defect (VSD) or patent ductus arteriosus (PDA)): Large left-to-right shunts lead to excessive volume loading of the left heart, particularly in the first 2 months of life as pulmonary resistance drops. Volume overload results in left atrial dilation, progressive LV dysfunction, and elevated LV filling pressure, which is transferred retrograde to the pulmonary veins, leading to pulmonary edema. Left ventricular function is often initially preserved, and must increase dramatically in the setting of a left-to-right shunt in order to maintain cardiac output. Output will be normal until the pulmonary bloodflow-to-systemic-bloodflow ratio exceeds a threshold level, after which cardiac output drops and hypoperfusion symptoms ensue. Cyanotic heart disease can also be associated with pulmonary overcirculation and heart failure, including truncus arteriosus, transposition of the great arteries, total anomalous pulmonary venous connection (TAPVR), double-outlet right ventricle (DORV), and single ventricle lesions with parallel systemic and pulmonary circulations.

   
   
3. 
   

   Acute valvar regurgitation lesions (e.g., acute mitral or aortic valvar regurgitation): Acute severe aortic or mitral valvar regurgitation involves reflux of volume into poorly compliant chambers (left ventricle or left atrium, respectively) resulting in elevated left ventricular filling pressures, elevated left atrial pressures, and pulmonary venous congestion. Ventricular function is often initially preserved.