Definition

Heart failure is defined as the inability of the heart to pump sufficient cardiac output to meet the metabolic needs of the body and supply it with enough oxygen. Depending on the section of the heart affected, a distinction is made between left heart, right heart, and global failure. Heart failure is also divided into acute and chronic heart failure according to the course of the disease.

Epidemiology

No precise epidemiological data are available on heart failure in children and adolescents. Congenital heart defects in neonates occur with a frequency of 8 to 11 per 1,000 live births—that is, about 1% of all live births. Only a fraction of these individuals develop symptoms of heart failure, estimated to be 0.1–0.2% of all live births.

Etiology

Heart failure is a result of congenital or acquired heart disease that leads to a volume or pressure overload of the heart or to myocardial insufficiency (Table 19.1). Furthermore, arrhythmias can lead to insufficient cardiac output.

In childhood, congenital heart defects that lead to volume or pressure overload of the heart are the most common causes of heart failure. Examples of volume overload are a large ventral septal defect (VSD), patent ductus arteriosus (PDA), or atrioventricular septal defect (AVSD). Pressure overload develops in aortic stenosis, coarctation of the aorta, or mitral stenosis, for example.

The clinical symptoms of heart failure in the various congenital heart defects typically manifest at certain times (Table 19.2). Congenital heart defects with a large left-to-right shunt, for example, usually lead to heart failure when pulmonary resistance drops at the age of 6 to 8 weeks. An atrial septal defect (ASD) usually does not lead to heart failure until adulthood. In most cases, children with tetralogy of Fallot do not develop heart failure, as they are protected from a large shunt volume and corresponding volume overload due to pulmonary stenosis.

Pathophysiology

The body reacts to the decreased pumping capacity of the heart with various compensatory mechanisms that initially improve the blood supply to the body, but over time contribute considerably to deterioration of cardiac condition.

Neuroendocrine activation

The increase in the sympathetic tonus, and thus the increased release of catecholamines initially leads to an increase in the heart rate and contractility. However, over time, downregulation of the beta-adrenergic receptors occurs so that the effectiveness of the catecholamines in the heart decreases. Because of an increase in systemic vascular resistance, the afterload increases.

The activation of the renin–angiotensin–aldosterone system (RAAS) leads to an increase in the afterload due to vasoconstriction and to an increase in the preload due to sodium and water retention. Increased secretion of antidiuretic hormone (ADH) results in excessive water retention.

The increased pressure and volume load also leads to activation of the NO and the natriuretic peptides ANP (atrial natriuretic peptide), BNP (brain natriuretic peptide), and CNP (C-type natriuretic peptide). They cause vasodilatation and an inhibition of the RAAS as well as natriuresis, in effect a counter-regulatory mechanism.

NT-pro-BNP (N-terminal pro brain natriuretic peptide), a precursor of BNP, is also used as a laboratory chemical marker of heart failure. The serum levels of the natriuretic peptides rise with increasing heart failure.

The recombinant form of BNP, nesiritide, is currently used in clinical trials for the treatment of acute heart failure due to its vasodilator properties.

Frank–Starling mechanism

An increase in the preload (e.g., through activation of RAAS and increased secretion of ADH) initially causes an improvement in contractility and an increase in stroke volume, but over time, the increases in end-diastolic pressure and afterload (also consequences of the neuroendocrine compensatory mechanisms) lead to a decrease in cardiac pump function.

Myocardial hypertrophy

Chronic volume overload leads to dilatation and thus to eccentric hypertrophy. By contrast, pressure overload leads to concentric hypertrophy with an increase of heart wall thickness. These remodeling processes initially improve the pumping function of the heart, but with increasing hypertrophy, the oxygen demand of the myocardium increases disproportionately.

Symptoms

Most affected children have global heart failure; it is rarely possible to distinguish between right heart failure and left heart failure.

Infants and younger children have a history of poor feeding, failure to thrive, tachypnea (especially under exertion, such as drinking), and increased sweating (especially on the forehead). In older children, the main symptoms are dyspnea or shortness of breath under stress, rapid fatigability, and eyelid or foot edema.

On clinical examination, the following findings are indicative of heart failure:

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  Tachycardia: due to increased sympathetic tone.

  
  
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  Gallop rhythm: A third or fourth heart sound is probably a sign of rapid filling of a relatively stiff ventricle.

  
  
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  Cool limbs, pallor, prolonged capillary refill time: signs of peripheral vasoconstriction and reduced peripheral perfusion in sympathetic activation.

  
  
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  Tachypnea, dyspnea, subcostal and intercostal retractions, orthopnea: Tachypnea is the clinical manifestation of the excessive pulmonary blood flow and pulmonary edema. With advancing heart failure, ventilation function is increasingly impaired. Dyspnea with subcostal and intercostal retractions develops. Manifest pulmonary edema causes fine bubbly crackles. Frequent pulmonary infections are also a result of excessive pulmonary blood flow. A dry cough can also be a sign of excessive pulmonary blood flow or pulmonary congestion.

  
  
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  Pulsus tardus: Arterial pulses weak on palpation.

  
  
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  Pulsus paradoxus

  
  
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  Cyanosis: Sign of increasing oxygen utilization in the periphery or deterioration of gas exchange as a result of pulmonary edema. Cyanosis may also be indicative of an increasing right-to-left shunt.

  
  
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  Hepatomegaly: Sign of systemic venous congestion in the context of right heart failure or global failure.

  
  
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  Jugular vein distention: Occurs mainly in older children and adults as a sign of a systemic venous congestion. It is rarely observed in younger children.

  
  
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  Edema: Mainly eyelid edema in children. Peripheral edema is less common than in adults.

Similar to adults, the clinical severity of heart failure is divided in four NYHA classes. The criteria have been modified for children (Table 19.3).