Shock and cardiac disease in children

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Chapter 101 Shock and cardiac disease in children

Most cases of shock in childhood are caused by hypovolaemia (Table 101.1) or sepsis. The causes, clinical course, management and complications of shock differ from those in adults: severe diarrhoeal disease and congenital abnormalities are common in childhood but abdominal sepsis, pancreatitis and obstructive vascular disease are uncommon.

Table 101.1 Causes of hypovolaemic shock in childhood

Bleeding

Revealed (external or into the gastrointestinal tract)

Concealed (scalp, intracranial, trunk or limbs)

Water and electrolyte loss

Bowel

Renal

Skin

Plasma loss (capillary leak)

Water deprivation (absolute or relative to losses)

The following factors affect the epidemiology of shock in children:

SMALLER BODY FLUID COMPARTMENTS

A small volume of blood or diarrhoeal fluid loss, or of fluid leakage into the extravascular space may represent a large percentage loss of blood or extracellular fluid (ECF) volume in a small child (Table 101.2).

Table 101.2 Body fluid compartments during childhood (ml/kg)¹

IMMATURE IMMUNE SYSTEM IN INFANTS AND TODDLERS ²

The innate host defences of the small child are immature: the skin and the respiratory and gut mucosae are more permeable to bacteria and their toxins, and secretory IgA levels remain low throughout childhood. There is increased susceptibility to severe bacteraemias due to:

• low IgM and IgG levels

• deficient neutrophil adhesion, migration and respiratory burst activity, combined with lower levels of complement (especially C3, C9 and factor B)

• low cytokine production by monocytes

Antibody response to bacterial polysaccharide capsular antigens (e.g. Streptococcus pneumoniae, Haemophilus spp. and Neisseria meningitidis) remains poor in the preschool years. Low IgG concentrations, immunological naivety and reduced natural killer (NK) cell activity predispose young children to frequent viral infections, and the newborn to severe herpes simplex infection.³

Reduced cytokine production, especially in the immunologically naive, may alter the features and duration of the shock syndrome, including the ability to develop a fever, and causes deficiency in most T-cell functions, including cytotoxicity and augmentation of B-cell differentiation.⁴

MICROBIOLOGY

In the newborn, septic shock is most often caused by Staphylococcus aureus, group B β-haemolytic streptococci, Enterobacteriaceae, Listeria monocytogenes, enteroviruses (e.g. Echo or Coxsackie viruses) or herpes simplex virus.

Later in childhood, Strep. pneumoniae, N. meningitidis, Haemophilus influenzae, Staph. aureus and Enterobacteriaceae cause most cases of septic shock. Although severe sepsis due to H. influenzae type b (Hib) and N. meningitidis group C has been almost completely eradicated among immunised children, cases of severe sepsis involving these organisms still occur in non-immunised children, and cases of sepsis due to other serotypes are seen in immunised children.

In immunodeficient children, Staph. aureus, Enterobacteriaceae, Pseudomonas spp., Candida albicans, fungi and viruses such as cytomegalovirus and varicella frequently cause septic shock.

SEVERE CONGENITAL ABNORMALITIES

Children with congenital heart, lung or neurological diseases, multiple congenital abnormalities, inborn errors of metabolism and the inherited immunodeficiency syndromes are prone to develop cardiogenic, hypovolaemic or septic shock, especially in the first 2–3 years of life.

OTHER CHILDHOOD CONDITIONS THAT PREDISPOSE TO SEVERE SEPSIS

These include:

• cancer and its chemotherapy

• organ transplantation (especially bone marrow)

• multiple trauma

• burns

• prolonged paediatric intensive care unit (PICU) stay

• the presence of implanted therapeutic devices including intravascular catheters

PATHOPHYSIOLOGY

The pathophysiology of shock is described in Chapter 11 which should be read in conjunction with this chapter. The following aspects of a child’s physiology affect the response to insults.

IMMATURE CARDIOVASCULAR SYSTEM ^5,⁶

LESS CAPABLE OF DEVELOPING CONTRACTILE FORCE

The immature myocardium has more loose connective tissue than the adult, but fewer sarcomeres per gram of tissue. The arrangement of myofibrils in the myocyte, and of myocytes in the myocardium, is less parallel than in the adult. Intracellular desmin fibrils which link the contractile elements are more randomly arranged in the infant heart. Less efficient calcium uptake, storage and release from sarcoplasmic reticulum (SR) and a higher density of cell membrane Na/Ca exchangers mean that excitation–contraction coupling is more dependent on trans-sarcolemmal Ca⁺⁺ flux, and on ECF Ca⁺⁺ concentration than the adult.

LESS DIASTOLIC COMPLIANCE THAN THE ADULT HEART

• Limited calcium uptake and storage into SR, more slow skeletal troponin I and more β-tropomyosin relative to α-tropomyosin mean slower diastolic relaxation of the ventricles.

• Greater myocardial collagen content and immaturity of the cytoskeleton and intercellular matrix increase the diastolic elastic recoil of the infant ventricular wall.

• Increases in end-diastolic volume of either ventricle cause greater reduction of compliance of the opposite ventricle than in the adult: when right ventricle (RV) afterload rises acutely, the consequent increase in RV end-diastolic volume distorts the left ventricle (LV) and impairs LV filling and emptying more than in the adult.

MORE TOLERANT OF HYPOXAEMIA

Although the infant heart has fewer mitochondria per gram of tissue, and a lower oxidative capacity, it has a lower oxygen demand per gram, larger glycogen reserves and a higher capacity for anaerobic glycolysis.⁷ Glucose is the major myocardial energy source (rather than long chain fatty acids as in older children) and hypoglycaemia causes severe myocardial depression.

IMMATURE AUTONOMIC INNERVATION

Parasympathetic innervation of the heart is more complete than sympathetic in infants, and the infant response to severe stress (e.g. hypoxia) tends to be bradycardia rather than tachycardia.

The infant myocardium has fewer β-receptors, more α-receptors, and is more sensitive to noradrenaline (norepinephrine) than the adult. Stimulation of myocardial α-receptors in the infant is more likely to cause tachycardia than bradycardia.⁸

HIGH PULMONARY VASCULAR RESISTANCE ⁸

In the fetus, the small pulmonary arteries are narrow, the pulmonary vascular resistance is high, and pulmonary blood flow is less than one-tenth of systemic flow. A thick layer of smooth muscle, which extends further out into the vascular tree than in the adult, is highly sensitive to hypoxia, hypercarbia, acidaemia, sepsis and central neural stimuli such as pain.

At birth, after the first breaths are taken, the smooth muscle cells gradually relax and become more fusiform in shape. Pulmonary vascular resistance falls immediately, then gradually declines to adult levels by 6–8 weeks of age, and smooth muscle bulk falls to adult levels by 3–4 months.⁹ In the presence of lung disease, high pulmonary venous pressures (e.g. due to aortic stenosis or stenosis of the pulmonary veins) or large left-to-right shunts (e.g. ventricular septal defect (VSD) or truncus arteriosus), the high pulmonary vascular resistance and the extensive and bulky vascular smooth muscle fail to decline normally. The infant is then vulnerable to episodes of acute right heart failure whenever the pulmonary vascular resistance increases abruptly.

CLINICAL PRESENTATION OF SHOCK IN CHILDHOOD

HYPOVOLAEMIC SHOCK (SEE Table 101.1)

The child may have a history of fluid or blood loss, reduced fluid intake or bowel-related illness. Signs of dehydration (see Chapter 99), external bleeding or haematoma may be present. The presence of hypovolaemic shock implies a blood volume deficit greater than 30 ml/kg.

Signs of homeostatic compensation, such as tachycardia (Table 101.3), narrow pulse pressure, cool mottled limbs and slow capillary refill usually precede the onset of hypotension, which tends to occur late (after loss of 15–20% of blood volume) and precipitously in young children. In severe shock of any cause, signs of multiple organ hypoperfusion (e.g. oliguria of less than 0.5 ml/kg per hour, lethargy or coma, hypothermia, tachypnoea and increasing lactic or other metabolic acidosis) are found. Bleeding due to disseminated intravascular coagulation and liver dysfunction may occur in the first 6 hours.

Table 101.3 Normal blood pressure, heart rate and respiratory rate in childhood ¹⁰

In early shock, these changes are reversible by plasma volume expansion with boluses of 20 ml/kg 0.9% saline or blood, repeated as necessary. Failure to respond to two such boluses with a decrease in heart rate and capillary refill time (normal < 2 seconds after 5 seconds’ pressure over the sternum) indicates refractory shock requiring more aggressive treatment (see below).

Investigations (see Table 101.4) include:

• daily weighing and comparison with pre-illness weight

• close monitoring of fluid balance

• stool culture and examination for occult blood

• imaging of body cavities by CT or ultrasound for evidence of fluid or blood accumulation

• repeated full blood examination and coagulation screen

• plasma urea and electrolytes

• serum and urine osmolality

Table 101.4 Investigation of shock in children

All shocked children

Arterial blood gases

Plasma electrolytes, urea, creatinine, glucose, liver function tests, lactate

Haemoglobin, platelet count, total and differential white cell count

Coagulation screen including fibrin degradation products

Blood group (hold serum)

If the cause of shock is unknown

Exclude sepsis:

Several sets of blood cultures, percutaneous and via vascular catheters

Culture and Gram stain pus

Urine cultures from mid-stream sample or suprapubic aspirate of urine

Urine, stool and nasopharyngeal aspirate for virology

CSF bacterial and viral culture plus PCR for specific organisms

Urine bacterial antigens

To exclude cardiogenic shock: echocardiography, ECG, cardiac catheter

Drug screen: urine, gastric aspirate, blood

Metabolic screen: urinary amino acids and organic acids, plasma ammonia and glucose

Short Synacthen test

CSF, cerebrospinal fluid; ECG, electrocardiogram; PCR, polymerase chain reaction.

CARDIOGENIC SHOCK

Tachycardia, hypotension, low volume pulses and signs of homeostatic compensation and poor organ perfusion (see above) are usually present. Cardiomegaly, muffled heart sounds and a gallop rhythm may be found. New murmurs may appear (e.g. mitral systolic murmur due to left ventricular dilatation with consequent mitral regurgitation, or aortic diastolic murmur due to endocarditis). Chest rales, tachypnoea and wheezing indicate left heart failure, while in right heart failure, oedema appears first in the eyelids and dorsum of hands and feet. Hepatomegaly develops rapidly in children, and is a more reliable sign of right heart failure than a raised jugular venous pressure (JVP) which may be hard to detect in infants.

Combinations of signs specific to individual congenital heart lesions are described below. Such signs when present (e.g. absent femoral pulses in aortic coarctation, or skull, liver or renal bruits of arteriovenous fistulae) may indicate the cause of the shock (Table 101.5), while diagnostically useful murmurs are not always present.

Table 101.5 Causes of cardiogenic shock in childhood

Investigations (see Table 101.4) should include:

• chest X-ray to assess heart size and lung vascularity and oedema, and to exclude pneumothorax

• electrocardiogram (ECG)

• echocardiography

• in some cases, CT or MR angiography or cardiac catheterisation

SEPTIC SHOCK

Septic infants usually present with a hypodynamic circulation, low cardiac output and cool extremities. Early septic shock in older children may be hypodynamic, or may be similar to that in adults, in which tachycardia, tachypnoea and hypotension are accompanied by warm extremities, wide pulse pressure and increased cardiac output. Lethargy or stupor, oliguria and Kussmaul breathing characteristic of metabolic acidosis indicate inadequate tissue oxygenation.

Severely septic children are often hypothermic rather than febrile.

As shock progresses, myocardial depression by endotoxin, tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) (see Chapter 11) decreases the cardiac output earlier than is the case in adults, as the less compliant infant ventricle cannot dilate to sustain the stroke volume in the face of a reduced ejection fraction.^11,¹² Furthermore, the rapid and severe capillary leak that is characteristic of paediatric sepsis leads to hypovolaemia in the underresuscitated child, further reducing preload and cardiac output. For this reason, septic children often respond well to aggressive fluid resuscitation (> 60 ml/kg in the first hour). Peripheral oedema caused by leakage of proteinaceous fluid from injured capillary endothelia exacerbates cellular hypoxia by increasing the diffusion distance for oxygen between capillaries and cells.

MULTIPLE ORGAN FAILURE IN SHOCKED CHILDREN

Shock of any cause leads to multiple organ failure, the clinical course and outcome of which differ from those in shocked adults:

• Myocardial depression, reduced ventricular diastolic compliance ¹³ and low cardiac output. Clinically important arrhythmias rarely occur.

• Acute lung injury can occur in a shocked child of any age, including the newborn. Respiratory muscle fatigue due to impaired muscle blood flow and oxygenation further reduces gas exchange.

• Acute renal failure occurs frequently, is usually reversible within 50 days, may require haemodiafiltration or peritoneal dialysis, and is rarely a significant contributor to mortality in shocked children.

• Disseminated intravascular coagulation occurs very commonly, due to activation of the coagulation pathway, increased production of plasminogen activator inhibitor-1 and reduced levels of proteins C and S, antithrombin III and thrombomodulin.¹⁴ This contributes to failure of other organs, and combines with impaired liver function and clotting factor dilution by fluid resuscitation to cause bleeding from puncture sites and sometimes from the upper gastrointestinal tract.

• Bone marrow failure, with anaemia, granulocytopenia and thrombocytopenia, implies severe shock and is associated with a poor outcome, especially in sepsis.

• Gastrointestinal failure with paralytic ileus is often present. Significant upper gastrointestinal bleeding occurs less commonly in shocked children than in adults. The source is usually generalised oozing from gastric mucosa which responds to proton pump inhibitors and replacement of platelets and clotting factors.

• Plasma concentrations of liver enzymes and bilirubin are often raised but return to normal over a few days in survivors.

• Acalculous cholecystitis due to splanchnic ischaemia is sometimes found in older children.

• Encephalopathy with stupor or coma occurs commonly. The appearance of seizures suggests some complication of sepsis, such as glucose or electrolyte abnormality, meningitis, septic embolus or intracranial bleeding.

DISTRIBUTIVE SHOCK

The main features are hypotension, vasodilatation and hypovolaemia due to plasma leakage from capillaries. The child’s extremities are warm and pink, the blood pressure is low and the pulse pressure is wide. There is tachycardia, oliguria and stupor. Other evidence of anaphylaxis (wheezing, urticaria, swollen face or tongue), spinal cord injury (bradycardia, quadriparesis, lax anal sphincter) or drug intoxication (history, tablets, coma out of proportion to shock) may be present (Table 101.6).

Table 101.6 Causes of distributive shock in childhood

Sepsis

Anaphylaxis

Drugs

Neurogenic: spinal cord injury

INVESTIGATION

See Table 101.4.

MANAGEMENT

The child’s airway, breathing (see Chapter 98) and circulation should be secured during the initial assessment. The priorities in management of the circulation are to achieve:

1 adequate perfusion of the brain and heart

2 adequate perfusion of kidneys, liver and gut

3 adequate perfusion of muscle and other tissues

ADEQUATE PERFUSION OF THE BRAIN AND HEART

This requires systolic and diastolic blood pressures of 80% of normal for age (see Table 101.3), achieved by aggressive early blood volume expansion and by pressor drugs. The conscious state is the best index of adequate brain perfusion, while improved coronary perfusion is shown by rising blood pressure with falling central venous pressure.

Preload

Intravenous fluid is given in boluses of 20 ml/kg 0.9% saline or 10 ml/kg blood or colloid, repeated every 5–10 minutes until blood pressure, heart rate and skin vasoconstriction (capillary refill time: normal < 2 seconds after 5 seconds’ pressure over the sternum) and indices of organ perfusion (i.e. urine output, conscious state, blood pH and lactate) improve. Heart and liver size and increases in central venous pressure (CVP) are used to assess hypervolaemia. If more than 40 ml/kg crystalloid is given:

• consider starting an infusion of a pressor drug (sepsis and other distributive shock) or an inotrope (see below)

• monitor central venous pressure

• insert an arterial cannula for blood pressure and biochemical monitoring

Pulmonary artery catheterisation for measurement of wedge pressure and cardiac output is rarely justified in children: evidence that it improves outcome is lacking,¹⁵ and side-effects occur commonly.¹⁶ Non-invasive monitoring of left and right ventricular preload by transthoracic echocardiography may be more useful than atrial pressure measurement, in that it removes the confounding factors of diastolic compliance and atrioventricular (AV) valve dysfunction, but it is subjective and operator dependent.¹⁷

Systemic vascular resistance

In septic or hypovolaemic shock, infusion of noradrenaline (0.05–2.0 μg/kg per min) should be started (via an intraosseous cannula when no central venous cannula is in place) if volume expansion does not achieve 80% of normal systolic blood pressure for age within 10 minutes. In septic shock, vasopressin (0.0003–0.0006 U/kg per min), the action of which does not depend on downregulated α₁-receptors, may be used to reduce the dose of noradrenaline required. Vasopressin deficiency occurs commonly in septic shock ¹⁸ and in irreversible shock of other causes.¹⁹

Contractility

If the blood pressure then remains low despite CVP = 12 mmHg or ‘adequate’ LV filling on transthoracic echo, an inotrope such as adrenaline (0.05–2.0 μg/kg per min), dobutamine or dopamine (5–15 μg/kg per min) should be added. Dobutamine and dopamine downregulate β-adrenergic receptors, and dopamine depletes myocardial noradrenaline stores, so the dose of these drugs should be minimised as soon as possible. β-Agonists increase oxygen consumption (and therefore oxygen demand) by increasing free fatty acid cycling and by increasing glycogenolysis and glycolysis.²⁰ Dopamine suppresses prolactin, thyroid-stimulating hormone and growth hormone secretion in infants and children.²¹

In infants with cardiogenic shock, infusion of 10% calcium gluconate (0.2–0.5 ml/hour) can increase blood pressure and cardiac output. Serum ionised calcium should be monitored.

ADEQUATE PERFUSION OF KIDNEYS, LIVER AND GUT

Bowel and liver ischaemia in a shocked child impairs detoxification of drugs and toxic metabolites and may increase the risk of bacteraemia and endotoxaemia of bowel origin.²² Hypovolaemia and low cardiac output must be corrected by blood volume expansion and inotropic drugs such as dobutamine. Vasoconstricting drugs (vasopressin, noradrenaline and dopamine doses > 5 μg/kg per min) should be reduced or stopped once heart and brain perfusion are secured.

Urine output > 0.5 ml/kg per hour and a normal (or falling) plasma creatinine concentration are the best indices of adequate renal perfusion. Monitoring of splanchnic perfusion remains unreliable. Gastric pH and gastric–arterial PCO₂ difference correlate somewhat with outcome in septic children (though not as well as plasma lactate)²³ and are not consistently improved by measures to restore bowel perfusion.²⁴ Oesophageal–arterial PCO₂ difference²⁵ and near-infrared spectroscopy of the liver²⁶ may offer more accurate monitoring of the adequacy of splanchnic blood flow.

ADEQUATE PERFUSION OF MUSCLE AND OTHER TISSUES

Further volume expansion and infusion of vasodilators such as milrinone may be needed to improve circulation to these tissues in shock states where myocardial depression is prominent, provided an adequate blood pressure (80% normal for age; see Table 101.3) can be sustained. Maintaining a supranormal cardiac output and oxygen delivery has not been shown to improve survival in paediatric shock, although the ability to do so may predict survival.

In the absence of a pulmonary artery catheter, the adequacy of upper or lower body blood flow is conventionally assessed by monitoring changes in central venous saturation ²⁷ and plasma lactate, though the oxygen excess factor Ω (SaO₂/(SaO₂ – SvO₂) has been used in children with intracardiac shunts.²⁸

Afterload reduction in cardiogenic shock

Vasoconstrictors and blood transfusion (to achieve a haemoglobin concentration of 120 g/l) may be required at first to ensure adequate coronary and cerebral perfusion pressure. When blood pressure is adequate (see Table 101.3), the cardiac output may be improved by afterload reduction. Short-acting drugs such as milrinone or sodium nitroprusside (SNP) are preferable.

Inhaled nitric oxide (NO) 1–10 ppm via the ventilator circuit may improve RV output in children with cardiogenic shock due to pulmonary hypertension (primary or after cardiac surgery or in persistent pulmonary hypertension of the newborn). Sildenafil and bosentan have been shown to reduce pulmonary vascular resistance and to permit weaning from NO in this group of children.²⁹

Infusion of vasodilators such as nitroglycerin, prostacyclin (PGI₂) and SNP reduces systemic as well as pulmonary vascular resistance. These drugs are easier to administer than NO, but are less effective pulmonary vasodilators, and they (and sildenafil and bosentan) often cause systemic hypotension.

After appropriate samples are taken for investigations (see Table 101.4), possible sepsis is treated aggressively with appropriate antibiotics (Table 101.7), replacement of invasive lines and drainage of collections of pus.

Table 101.7 Initial antibiotic therapy in children with septic shock

Up to 8 weeks of age

Flucloxacillin 50 mg/kg i.v. 6-hourly plus

Gentamicin 6 mg/kg i.v. per day plus

Cefotaxime 50 mg/kg i.v. 6-hourly

Older child

Flucloxacillin 50 mg/kg i.v. 6-hourly

Gentamicin 6 mg/kg i.v. per day

Supportive measures

Early mechanical ventilation secures adequate oxygenation and pH of arterial blood. It also reduces the work of breathing and muscle oxygen demand, diverting the limited cardiac output away from muscles to vital organs. Airway pressures and tidal volumes should be limited to the minimum needed, as impaired venous return from positive-pressure ventilation will exacerbate hypotension.

Other measures include administration of platelets and fresh frozen plasma in consumptive coagulopathy, early commencement of renal support with haemodiafiltration or peritoneal dialysis in established acute renal failure and the use of H₂ antagonists or proton pump inhibitors to prevent upper gastrointestinal bleeding.

Controversial measures

• Stress dose of hydrocortisone (4 mg/kg per day for ∼5 days): Reduced 28-day all-cause mortality and ICU and hospital mortality in septic shock.³⁰

• Granulocyte–macrophage colony-stimulating factor: A randomised trial found that it reduced mortality in severely ill septic, neutropenic newborns.³¹

• Intravenous pooled polyclonal immunoglobulin (IVIG): Some evidence of reduced mortality from controlled trials in severe sepsis.³²

• Recombinant bactericidal permeability-increasing protein (rBPI₂₁): Trend to improved functional outcome in a small trial in children with severe meningococcal sepsis.³³

• Granulocyte transfusions for severe sepsis with neutropenia: Trend to improved outcome when combined with IVIG in a controlled trial in septic newborns.³⁴

• High-dose steroids after antibiotics started: Pre-1992 trials showed no benefit.³⁰

• Monoclonal anti-endotoxin, anticytokine antibodies or IL-1 receptor antagonists: No evidence of efficacy in controlled trials.³²

• Activated protein C: No evidence of improved outcome in a controlled trial in severely septic children.³⁵

• Tri-iodothyronine (T₃): No convincing evidence of improved outcome in trials in children with low cardiac output after cardiac surgery despite evidence that T₃ is deficient in these patients.³⁶

• Circulatory support with extracorporeal membrane oxygenation (ECMO): ECMO has been employed in children moribund with septic shock, with some survivors, but there is no convincing evidence of its efficacy.³⁷

• Close control of blood glucose using insulin infusion. There is no evidence in children that it improves outcome. Infants are very vulnerable to hypoglycaemia and are sensitive to low insulin doses. Blood glucose should be monitored frequently in shocked children.

HEART FAILURE IN CHILDREN

In cardiac failure, the cardiac output is insufficient to meet the metabolic needs of the tissues without development of abnormally high ventricular end-diastolic volumes.³⁸

Table 101.8 shows the main causes of heart failure in children. In many cases, several factors combine to produce heart failure (e.g. sepsis plus valve regurgitation and amiodarone).

• Preload may be:

• excessive: volume loading, e.g. systemic arteriovenous malformation, large ventricular septal defect, aortopulmonary window, AV valve regurgitation or excessive fluid administration

• inadequate: e.g. mitral stenosis, pericardial tamponade, hypertrophic cardiomyopathy or congenital hypoplasia of the left or right ventricle. Ventricular diastolic compliance may be reduced by ischaemia, postoperative myocardial oedema, sepsis, heart transplant rejection or cardiomyopathy (infiltrative or hypertrophic).

• Excessive afterload (ventricular systolic wall tension) may be caused by pulmonary valve stenosis or pulmonary hypertension (right ventricle); by aortic valve stenosis, aortic coarctation or hypoplasia or systemic hypertension (left ventricle); or by ventricular dilatation.

Table 101.8 Common causes of heart failure from infancy to adolescence

Heart failure presenting at birth

Birth asphyxia

Sepsis

Severe anaemia

Obstructive left-sided lesions presenting after closure of the ductus arteriosus (e.g. coarctation, aortic stenosis, interrupted aortic arch, hypoplastic left heart syndrome)

Aortopulmonary window, truncus arteriosus

Systemic AV fistula (e.g. liver, brain, kidney)

Congenital cardiomyopathy

Arrhythmia: congenital SVT or heart block

Persistent pulmonary hypertension of the newborn

Heart failure presenting in the first 8 weeks of life

Large left-to-right shunts (e.g. VSD, PDA, total anomalous pulmonary venous drainage) cause heart failure as pulmonary vascular resistance and the haematocrit decrease

Infiltrative cardiomyopathy

Anomalous origin of the left coronary artery from the pulmonary artery

Hypothyroidism

Heart failure presenting later in childhood

Congenital heart disease

Subaortic stenosis

VSD with or without aortic regurgitation

Systemic AV valve regurgitation

Pulmonary atresia and VSD with large aortopulmonary collaterals

Congenital heart disease post operation

Fontan procedure

Obstructed prosthetic valve

Post ventriculotomy (e.g. Fallot’s tetralogy)

Coronary artery injury

Imperfect myocardial preservation during bypass

Valve regurgitation after aortic or pulmonary valvotomy

Large Blalock–Taussig shunt

Cardiomyopathy

Infective, infiltrative, neuromuscular disease

Asphyxia (e.g. near-drowning, smoke inhalation)

Ischaemia (e.g. Kawasaki disease)

Toxic: acute (e.g. eucalyptus oil, carbamazepine, verapamil, flecainide)

Toxic: chronic (e.g. anthracycline)

Metabolic (e.g. LCAD deficiency)

Heart transplant rejection

Valvular (e.g. postrheumatic, infective endocarditis, trauma)

Arrhythmia (e.g. SVT, complete heart block)

Severe polycythaemia or anaemia (haematocrit > 70% or < 15%)

Cor pulmonale (e.g. bronchopulmonary dysplasia, severe scoliosis)

Acute hypertension (e.g. glomerulonephritis, haemolytic–uraemic syndrome)

AV, arteriovenous; LCAD, long-chain acyl-CoA dehydrogenase; PDA, patent ductus arteriosus; SVT, supraventricular tachycardia; VSD, ventricular septal defect.

(Laplace’s Law: T = P × R/2 H, where T is systolic wall tension, P is ventricular pressure during systole, R is ventricular radius and H is ventricular wall thickness.)

• Inadequate contractility: e.g. due to myocarditis, sepsis or ischaemia.

• Heart rate may be:

• too fast (e.g. in supraventricular tachycardia or atrial flutter, ventricular filling time is inadequate and myocardial work is excessive).

• too slow (e.g. complete heart block).

PRESENTING SIGNS

In childhood, heart failure may present with growth failure. Feeding is slow and may cause sweating and dyspnoea. Useful signs are tachypnoea, cardiomegaly, hepatomegaly, gallop rhythm, tachycardia and cool, mottled extremities. There may be clinical and X-ray signs of lung congestion, oedema and air trapping (due to airway compression by distended blood vessels and airway mucosal oedema: seen in large left-to-right shunts such as VSD). In infants, the JVP is a difficult sign to elicit. The liver enlarges rapidly as the right atrial pressure increases, and oedema is often non-pitting, and located in the eyelids and the dorsum of the hands and feet.³⁹

INVESTIGATIONS

After a detailed history and clinical examination, investigations include:

• chest X-ray: for heart size, shape, position and lung vascularity

• electrocardiogram (ECG) and, if necessary, Holter monitoring

• echocardiography (usually transthoracic; less often transoesophageal): for structural abnormality; valve stenosis, regurgitation and structure; chamber size and filling; wall thickness; pericardial fluid and estimates of ventricular systolic and diastolic function; left-to-right and right-to-left shunts, and pulmonary artery pressure

• cardiac catheterisation when indicated to quantify shunts, measure pressures and elucidate anatomy.

Plus other investigations as indicated:

• CT angiography to demonstrate 3-dimensional extracardiac structures

• MR angiography

• blood gases; chromosomal analyses; viral culture of stool, blood and throat swabs; urine screen for amino- and ketoacids, and myocardial biopsy.

MANAGEMENT ^40,⁴¹

The development of heart failure in infancy is an emergency requiring urgent hospitalisation. Management priorities include the following:

• Correct precipitating factors (e.g. fever, infection, anaemia or hypertension).

• Diagnose and correct the underlying cause (e.g. correct an aortic coarctation; repair or replace a regurgitant valve; treat an arrhythmia or infection; correct anaemia).

• Support the systemic and pulmonary circulations and reduce systemic and pulmonary venous congestion:

• Give oxygen by mask or nasal prongs.

• Give diuretics such as furosemide and spironolactone to reduce ventricular preload and venous congestion. Spironolactone has been shown to reduce mortality in adults with cardiac failure by inhibiting ventricular remodelling and improving diastolic compliance. Addition of a sulphonamide diuretic such as metolazone or hydrochlorothiazide has been shown to produce a diuresis in children with oliguria resistant to furosemide after cardiac surgery.⁴² Restriction of fluid and salt intake, head elevation and venodilator drugs such as nitroglycerin (GTN) 1–10 μg/kg per min may be required. Preload reduction may depress the cardiac output in acute correctable lesions which obstruct ventricular inflow (e.g. cardiac tamponade).

• Reduce left ventricular afterload by infusion of milrinone (0.25–0.75 μg/kg per min) or sodium nitroprusside (0.5–5.0 μg/kg per min). Angiotensin-converting enzyme (ACE) inhibitors may be added carefully when the child’s heart is capable of increasing its output to sustain an adequate blood pressure. ACE inhibitors reduce mortality in early and late heart failure by improving ventricular performance and inhibiting myocardial remodelling. Vasodilators must be used cautiously in obstructive left-sided lesions to avoid myocardial ischaemia (due to reduced aortic diastolic pressure in the presence of ventricular wall hypertrophy. Vasodilators exacerbate volume loading in VSD or aortopulmonary shunts.

• Reduce right ventricular afterload in intubated children with nitric oxide (NO) (0.5–10.0 ppm). In non-ventilated children, and to permit weaning of nitric oxide, sildenafil (0.3 mg/kg 6-hourly enterally) or infusion of prostacyclin (PGI₂ 5–15 ng/kg per min) may be used.^29,⁴³

• Increase contractility acutely with i.v. infusion of dobutamine (2–10 μg/kg per min) or adrenaline (0.02–0.5 μg/kg per min). β-adrenergic agonists increase oxygen consumption, myocardial work and ventricular diastolic stiffness, and may provoke tachyarrhythmias. They should therefore be used in the lowest effective dose.

• Levosimendan infusion (12.5 μg/kg over 10 minutes, then 0.2 μg/kg per min for 24 hours) has been shown to improve haemodynamics and 31-day survival compared with dobutamine in adults with severe heart failure, even when combined with β-blockers.⁴⁴ It offers improvement in contractility without increasing myocardial oxygen consumption or downregulating β-receptors.

• Consider careful use of β-blockers when diastolic dysfunction is prominent and when the child’s circulation is sufficiently stable for β-agonists to be withdrawn. If the child tolerates infusion of a short-acting drug such as esmolol (50 μg/kg per min gradually increased to 200 μg/kg per min), a longer-acting agent such as carvedilol may be substituted.⁴⁵

• Mechanical ventilation improves myocardial performance by improving gas exchange and reducing acidaemia, work of breathing and left ventricular afterload.⁴⁶ When pulmonary hypertension is the main cause of heart failure, intubation and mechanical ventilation can improve RV output by improving gas exchange and allowing NO to be given, but a short inspiratory time and low positive end-expiratory pressure (PEEP; 4–5 cmH₂O) are used to avoid further raising pulmonary vascular resistance.

• Sedation and muscle relaxants reduce metabolic rate and the cardiac output needed to meet metabolic demands. In a child with severe heart failure, commencing an inotrope such as dobutamine 10 μg/kg per min via peripheral cannula if necessary, 30 minutes before intubation reduces the risk of severe hypotension during intubation.

• Ventricular assist devices (VAD) can maintain life for weeks to months in very severe but reversible cardiac failure pending ventricular recovery or heart transplantation. When severe respiratory failure complicates severe heart failure, ECMO may be needed. Aortic balloon counterpulsation is less feasible and much less often helpful in small children than in adults.

CONGENITAL HEART DISEASE

Children critically ill with congenital heart disease (CHD) often require urgent resuscitation before a definitive structural diagnosis is made. The appropriate management then depends on the mode of presentation. A paediatric cardiologist should be consulted immediately about all such children. Management of acute postoperative deterioration depends on the underlying condition, nature of surgery and cause of deterioration.

Congenital heart disease in children may present in the following ways.

SHOCK IN THE FIRST FEW DAYS OF LIFE ⁴⁷

The commonest CHD causes are obstructive lesions of the left heart, including coarctation of the aorta with or without VSD, aortic stenosis and hypoplastic left heart syndrome (HLHS). Differential diagnosis includes cardiomyopathy, systemic arteriovenous malformation (AVM), septicaemia, inborn error of metabolism, anaemia, congenital heart block and supraventricular tachycardia (SVT).

In left-sided obstructive lesions, shock develops as the ductus arteriosus closes. All pulses (especially the femoral pulses in the case of coarctation) are decreased or absent. Tachycardia, tachypnoea, oliguria, cool mottled extremities, metabolic acidosis, hepatomegaly, cardiomegaly and pulmonary oedema are often present. Murmurs are often absent.

Emergency management ⁴⁸ consists of prostaglandin E₁ infusion (start at 10 ng/kg per min and increase to 25 if necessary) to provide aortic blood flow from the pulmonary artery by opening the ductus arteriosus, dopamine infusion, NaHCO₃ 1 mmol/kg i.v. over 1 hour to correct metabolic acidosis, and mechanical ventilation (to reduce work of breathing, maintain normocarbia and prevent apnoea due to the PGE₁). Hypocarbia and a high FiO₂ should be avoided as they reduce pulmonary vascular resistance and divert blood flow to the lungs, thereby reducing systemic blood flow. Normoglycaemia and normocalcaemia should be maintained.

ACYANOTIC HEART FAILURE

IN THE FIRST WEEK OF LIFE ⁴⁷

Coarctation, aortic stenosis, cardiomyopathy (including obstructive cardiomyopathy in an infant of a diabetic mother) and endocardial fibroelastosis, anaemia, septicaemia, overtransfusion and systemic AVM can present as heart failure. Signs include poor feeding, tachycardia, tachypnoea, sweating, hepatomegaly, cardiomegaly, gallop rhythm, alar flaring, wheezing and expiratory grunt. Femoral pulses may be absent in coarctation and bruits are audible in skull, liver or kidneys in AVM. An aortic flow murmur may be present in anaemia or AVM.

Emergency management includes oxygen, diuretics and fluid restriction (to 50% of maintenance requirements; see Chapter 99). In severe failure, mechanical ventilation and inotropic drug infusion (see above) are started, and the child is transferred to a paediatric cardiac centre. When femoral pulses are absent or if aortic stenosis is suspected, i.v. infusion of PGE₁ (5–25 ng/kg per min) is started.

AFTER 2–8 WEEKS OF AGE

Systolic murmurs and signs of heart failure appear in infants with left-to-right shunts (such as VSD, patent ductus arteriosus (PDA), aortopulmonary window and AV septal defect) due to the physiological decreases in haemoglobin concentration and pulmonary vascular resistance at this time.

Emergency management includes diuretics and oxygen given via nasal prongs. Transfusion (to haemoglobin 13–14 g/dl) may reduce left-to-right shunt. If these measures fail to control heart failure, surgery is often needed, preceded if necessary by mechanical ventilation and inotropic drug infusion (see above).

CYANOSIS

PaO₂ greater than 150 mmHg (20 kPa) breathing 100% oxygen almost completely rules out cyanotic CHD. Most cyanotic CHDs have a PaO₂ less than 60 mmHg (8 kPa). A chest X-ray should be obtained urgently. Cyanosis due to CHD occurs when:

• pulmonary blood flow is reduced (e.g. pulmonary atresia)

• pulmonary and systemic circulations are not in series but are separate (e.g. transposition of the great arteries)

• saturated and unsaturated blood mix in the heart (e.g. anomalous pulmonary venous drainage)

CYANOSIS WITH PULMONARY OLIGAEMIA ON CHEST X-RAY

This is usually caused by stenosis at, below or above the pulmonary valve, or by tetralogy of Fallot. Deep cyanosis is present, often without murmurs or with a pulmonary ejection murmur. Tachypnoea may be present. Chest X-ray shows paucity of lung vessels and concavity in the pulmonary artery segment of the left heart border.

Emergency management ^47,⁴⁹

ARRHYTHMIAS IN CHILDREN ⁵⁰

SINUS BRADYCARDIA (See Table 101.3: 2ND–98TH CENTILE OF NORMAL HEART RATE FOR AGE)

Predisposing conditions include normal sleep, hypoxaemia, acidosis, hypotension, high intracranial pressure, cervical spinal cord injury, tracheal suction and drugs such as β-blockers, amiodarone and digoxin.

MANAGEMENT

No treatment is needed for asymptomatic bradycardia unless it is extreme. Correct any reversible cause. If the sinoatrial node is damaged, atropine (20 μg/kg) or isoprenaline infusion (0.1–0.5 μg/kg per min) or temporary transoesophageal or (in an older child) transvenous pacing may be used.

BRADYCARDIA–TACHYCARDIA (SICK SINUS) SYNDROME ⁵¹

The usual form is severe sinus bradycardia with junctional escape rhythm. It can cause syncope and even sudden death. Predisposing conditions include:

• congenital atrial anomalies (e.g. Ebstein’s anomaly and AV septal defects)

• extensive atrial surgery (e.g. Fontan and Senning operations)

• viral myocarditis

• congenital sinus node dysfunction

MANAGEMENT

Atrial pacing then treat tachyarrhythmias on their merits.

ATRIOVENTRICULAR BLOCK ⁵² (Table 101.9)

Often asymptomatic, but may present with fatigue, syncope or cardiac failure.

Table 101.9 Causes of atrioventricular block

Normal variant in newborn, adolescents, athletes

Structural heart abnormalities (atrioventricular septal defects or left atrial isomerism)

Post cardiac surgery (e.g. repair of ventricular septal defect or Fallot’s tetralogy, Konno procedure)

Maternal antibodies

Cardiomyopathies, myocarditis (including rheumatic) and muscular dystrophies

Drugs (e.g. carbamazepine overdose)

MANAGEMENT

• Acquired complete heart block should be paced, regardless of symptoms, as escape rhythms are unreliable.

• Symptomatic second or third degree AV block requires i.v. atropine, isoprenaline infusion (0.1–0.5 μg/kg per min) and, if necessary, external cardiac massage until pacing is established. Temporary transoesophageal or (in an older child) transvenous pacing may precede insertion of a permanent pacemaker.

• Congenital in infants: temporary, then permanent pacing if the heart rate is < 55 beats/min, regardless of symptoms.

• Congenital in an older child: temporary, then permanent pacing if the heart rate is < 50 beats/min or if symptomatic, or if there are ventricular escape beats or ventricular dysfunction.

SUPRAVENTRICULAR TACHYCARDIA (SVT)

RE-ENTRANT SVT

In younger children, an accessory AV pathway is usually present, which may conduct antegrade (pre-excitation, e.g. Wolff-Parkinson-White (WPW)) or retrograde (no pre-excitation; normal QRS). These AV re-entrant tachycardias may be episodic (e.g. precipitated by an extrasystole or a junctional escape beat) or may be permanent. The latter may be associated with heart failure in infants.

In older children and adolescents, a re-entrant pathway may exist in the peri-AV node area, and is sometimes associated with congenital heart lesions such as Ebstein’s anomaly, tricuspid atresia and AV canal defects, as well as post cardiac surgery, myocarditis, drugs, sepsis, acidosis and catecholamine administration.

Management

Older children

• As above.

• Verapamil (0.1 mg/kg i.v. over 30 minutes) or atenolol (0.05 mg/kg i.v. every 5 minutes until response, maximum of 2.5 mg or four doses, then 0.1 mg/kg every 12–24 hours) may also be used.

JUNCTIONAL ECTOPIC TACHYCARDIA (JET)^50,⁵²

Atrioventricular dissociation and ventricular rate 160–290 beats/min with narrow QRS complexes are seen on ECG. JET usually follows cardiac surgery, especially when myocardial function is poor and when surgery involves the AV node or its blood supply (e.g. Fontan operation or repair of VSD or AV septal defect). Postoperative JET can be fatal, but is usually self-limiting after 12–72 hours.

Management

• Reduce β-adrenergic stimulation: use low-dose noradrenaline or vasopressin to maintain blood pressure. Avoid the use of pancuronium as a muscle relaxant.

• Induce hypothermia to 34–35 °C for 2–3 days with 12-hourly brief normothermia to allow assessment.

• Amiodarone infusion: 25 μg/kg per min for 4 hours, then 5–5 μg/kg per min (max 1.2 g/24 hours).

• Consider procainamide (400 μg/kg per min for 25 minutes, then 20–80 μg/kg per min) or propafenone (2 mg/kg over 2 hours i.v., then 4 μg/kg per min): beware of hypotension.

JET is usually resistant to vagal manoeuvres, adenosine and overdrive pacing.

VENTRICULAR ECTOPIC BEATS AND VENTRICULAR TACHYCARDIA

Ventricular tachycardia (VT)⁵¹ is uncommon in childhood, but may present as syncope, poor feeding (in infants) or heart failure. The rate is 120–300 beats/min. The QRS axis is different from that of the underlying sinus rhythm. QRS duration is usually (but not always) prolonged (> 0.08 seconds). Supraventricular tachycardia with aberrant conduction is rare in children: more than 90% of wide-complex tachycardias in children are VT. Fusion or capture beats, AV dissociation and new bundle branch block also favour the diagnosis of VT.

Predisposing conditions include congenital heart lesions and their surgery (e.g. aortic and subaortic stenosis, with hypertrophy of the left ventricular wall), myocardial ischaemia, mitral valve prolapse, myocarditis, cardiomyopathy, the hereditary long QT syndromes, blunt chest trauma, hypokalaemia or hypomagnesaemia and drug toxicity (including digoxin, cocaine, phenothiazines and tricyclic antidepressants).