Cyanotic heart disease and tetralogy of Fallot spells

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5.1 Cyanotic heart disease and tetralogy of Fallot spells

1 Cyanosis is dependent on haematocrit and oxygen saturation.

2 Cyanosis is caused by arterial oxygen desaturation or increased capillary oxygen extraction.

3 The hyperoxia test helps differentiate cardiac from other causes of cyanosis:

• Measure SpO₂ in room air or low FiO₂;

• Remeasure SpO₂ in 100% O₂;

• If SpO₂ remains low consider a fixed intracardiac shunt (cyanotic congenital heart defect);

• If SpO₂ increases consider other causes, e.g. lung disease.

4 If a cardiac cause is suspected check the pulses, blood pressure, ECG, and chest X-ray. Consult with a neonatologist, paediatrician or cardiologist early.

5 Cyanosis may be due to a duct-dependent lesion. A prostaglandin infusion may be advised following consultation.

Introduction

Cyanosis is a bluish discolouration of skin and mucous membranes due to excessive concentration of reduced haemoglobin in the blood.¹ Cyanosis is evident when deoxygenated haemoglobin in the cutaneous veins reaches approximately 5 g dL^–1.2 Deoxygenated haemoglobin may occur either from arterial blood desaturation or increased oxygen extraction by peripheral tissue. Central cyanosis is produced as a result of arterial desaturation, i.e. aortic blood carrying deoxygenated haemoglobin. Isolated peripheral cyanosis may result from excessive deoxy-haemoglobin caused by extensive oxygen extraction.¹ Haemoglobin level affects the presence of cyanosis. Cyanosis is detected at a higher oxygen saturation in children with polycythaemia and is more difficult to detect in children with severe anaemia. Causes of cyanosis are listed in Table 5.1.1.

Table 5.1.1 Causes of cyanosis ²^–⁷
Differential diagnosis
Arterial oxygen desaturation (central cyanosis [pO₂ <50 mmHg]) 1. Airway • Airway obstruction 2. Breathing • Lung disease • Central nervous system depression (e.g. coma) • Respiratory muscle weakness • Reduced respiratory drive (e.g. morbid obesity) 3. Circulation • Intracardiac right-to-left shunt (e.g. cyanotic congenital heart disease, pulmonary hypertension) • Intrapulmonary shunt (e.g. pulmonary atrioventricular fistula)

Increased capillary oxygen extraction (peripheral cyanosis)

1. Circulatory shock, e.g. sepsis

2. Congestive heart failure

3. Environmental, e.g. cold

4. Acrocyanosis of the newborn (autonomic – may last 72 hours)

Abnormal haemoglobin (not related to level of oxygenation)

1. Methaemoglobinaemia (pO₂ >50 mmHg but low O₂ saturation)

Cyanotic congenital heart disease

Cyanotic congenital heart disease (CHD) generally presents in the neonatal period. In the newborn, mild cyanosis (mild hypoxia SaO₂ >85%) may be difficult to detect clinically. Other confounding factors may be acrocyanosis (a normal finding, which may last 72 hours), polycythaemia (giving the appearance of cyanosis) and dark skin (cyanosis is more difficult to detect). Cyanosis is better appreciated in natural light than in artificial light.

Arterial oxygen saturation should always be assessed with pulse oximetry when considering cyanosis in the newborn. The hyperoxia test may help distinguish cyanosis caused by cyanotic heart defects from other defects.²^–⁴^,⁸

Hyperoxia test

• Measure SpO₂ in room air or low FiO₂.

• Remeasure SpO₂ after 15 minutes in 100% O₂.

• If SpO₂ remains low, consider fixed intracardiac shunt (cyanotic congenital heart defect). Most cyanotic CHDs have a PaO₂ <60 mmHg (8 kPa).

• If SpO₂ increases, consider other causes, e.g. lung disease. PaO₂ > 150 mmHg (20 kPa) almost completely excludes cyanotic CHD.

Clinical features ²^,⁷

A comprehensive cardiac and respiratory examination is essential in any cyanosed child. The key features are:

• pulses – rate, rhythm, volume;

• blood pressure – all four limbs if the pulse volume is abnormal;

• precordial impulse – heaves, thrills;

• auscultation – abnormalities of P₂, murmurs;

• pre-and postductal oximetry (right arm versus left arm/legs) if there is differential cyanosis.

Investigations

Investigations are directed at likely causes, after history and clinical examination. They may include arterial blood gas, serum electrolytes, glucose levels, full blood count, haematocrit, and cultures.

The chest X-ray (CXR) can be very useful and should be examined carefully for heart size (normal cardiothoracic ratio in AP film is <0.6), oligaemic lung field with decreased pulmonary blood flow, e.g. tetralogy of Fallot, or pulmonary venous congestion with an obstructive lesion, e.g. totally anomalous pulmonary venous drainage (TAPVD), cor triatriatum.

Management

The presentation of cyanosis in an infant or child mandates urgent review by a neonatologist, paediatrician or paediatric cardiologist. Echocardiography may be necessary urgently. Early discussion with a neonatologist or cardiologist can help clarify possible diagnoses and initial management in the emergency department (ED) setting.

An important issue in the management of cyanosis in the newborn period is recognising the duct-dependent lesion. A duct-dependent lesion is one that results from the ductus arteriosus remaining patent so that blood flow is delivered to both the pulmonary and systemic circuits:

• Pulmonary atresia/critical pulmonary stenosis. The ductus shunts right-to-left to ensure adequate pulmonary blood flow.

• Coarctation of the aorta/critical aortic stenosis/interrupted aortic arch. The ductus shunts right-to-left to ensure adequate systemic blood flow.

• Transposition of the great arteries. Mixing is required usually at atrial, ductus and ventricular levels.

If a duct-dependent lesion is considered, consult a paediatric cardiologist or neonatologist before starting an intravenous infusion of prostaglandin E₁ (PGE₁, 5–25 ng^–1 kg^–1 min^–1). Important side effects are respiratory depression and fever. Avoid PGE₁ when a small heart accompanies cyanosis and pulmonary oedema, because these findings suggest TAPVD with obstructed veins (PGE₁ will worsen pulmonary oedema).

Chronic cyanosis stimulates a reactive polycythaemia that increases the oxygen-carrying capacity. When haematocrit reaches 65% or more, a large increase in blood viscosity occurs.

Hyperviscosity and coagulopathy often occur and in patients with a right-to-left intracardiac shunt may result in stroke and brain abscess.

Tetralogy spells

Introduction ²^–¹⁰

Hypercyanotic, hypoxic or cyanotic spells occur in young infants with tetralogy of Fallot. These occur most commonly under 6 months of age and may be precipitated by agitation from any cause. The cause is likely to be multifactorial, including a component of dynamic infundibular obstruction. The net result is an imbalance of pulmonary to systemic blood flow.

Tetralogy of Fallot consists of anterior deviation of the outlet septum leading to the characteristic morphological features of:

• subpulmonary infundibular stenosis ± pulmonary valve stenosis ± hypoplastic pulmonary arteries;

• subaortic perimembranous ventricular septal defect (VSD);

• aortic root overriding the crest of septum and VSD;

• secondary right ventricular hypertrophy;

Clinical features include:

• intense cyanosis;

• hyperpnoea and acidosis;

• quieter and shorter ejection murmur (compared to before the spell);

• irritability, lethargy, loss of consciousness, seizures, death.

Triggers include dehydration, exertion and emotional distress associated with crying (increases pulmonary vascular resistance and hence decreases pulmonary blood flow). The child may have a history of previous squatting. Spells are usually self-limiting though sequelae include hypoxic–ischaemic encephalopathy and death. Spells are less common since the advent of early systemic-pulmonary shunts or early corrective surgery.

Investigations

Investigations include laboratory testing and imaging as follows.

Laboratory

Blood gas analysis – usually shows acidosis with hypoxia.

ECG

The ECG in tetralogy of Fallot usually shows:

• right ventricular hypertrophy in the unipolar and standard leads;

• right axis deviation (+120° to +150°);

• dominant R wave in the right and a dominant S in the left precordial leads;

• Right atrial hypertrophy;

• normal PR interval and QRS duration;

• tall, peaked T waves;

• reversal of the RS ratio.

Chest X-ray

The classic coeur en sabot or boot-shaped cardiac silhouette is caused by the elevation of the apex due to right ventricular hypertrophy, combined with a concavity in the area of the main pulmonary artery. A right-sided aorta is present in 25% of tetralogy patients.

Echocardiography

An echocardiogram will accurately confirm tetralogy of Fallot but is not useful in acute management of spells.

Treatment ²^–⁶^,⁸^–¹³

If possible, the child should be in a quiet, calm environment. Being held in parents’ arms often diminishes crying and helps pulmonary blood flow.

The knee–chest or squatting position is preferred as it increases after-load, thus decreasing R to L shunting.

Supplemental high-flow oxygen (10–15 L min^–1 of 100% oxygen via mask) should be provided.

Monitoring includes continuous ECG monitoring, pulse oximetry, and non-invasive BP.

Morphine (0.1–0.2 mg kg^–1 intravenously (IV) or subcutaneously (SC)) should be used to treat hyperpnoea and decrease systemic catecholamines, and often aborts crying, which perpetuates the spell.

Consider a small fluid volume challenge (5–10 mL kg^–1) to increase preload and reduce dynamic outflow obstruction.

Propranolol (0.05–0.2 mg kg^–1 slow IV push over 10 minutes, repeat once every 15 minutes) can be used to block β-receptors in the infundibulum, thereby lessening RV outflow obstruction. Other β-blockers may be useful.

Phenylephrine (phenylephrine, 5–10 mcg kg^–1 IV [maximum SC/IM dose = 10 mg]) increases afterload, thereby decreasing right-to-left shunt. Alternatives include metaraminol (0.01 mg kg^–1 IV) or methoxamine (0.1 mg kg^–1 IV).

Consider NaHCO₃ (1–2 mmol kg^–1 IV) for correction of acidosis.

Check temperature and blood glucose. Correct hypoglycaemia and hypothermia.

Disposition

Organise hospital admission and paediatric cardiology consultation.

Failure to respond to the above treatment mandates intubation, ventilation and deep sedation or general anaesthesia and intensive care admission. Emergency surgery is rarely indicated.

1 Anderson D.M. Dorland’s Illustrated Medical Dictionary. Philadelphia: WB Saunders; 1994.

2 Park M.K. Congestive heart failure. In Park M.Y., editor: Pediatric cardiology for practitioners, 5th ed., Philadelphia: Mosby Elsevier, 2008.

3 Abelson W.H., Garth Smith R. Residents handbook of pediatrics, 7th ed. Toronto: The Hospital for Sick Children, Toronto, Canada, BC Decker Inc; 1987.

4 Guzman M.F., Hedley Brown A., Been M., et al. Manual of cardiorespiratory critical care. Sevenoaks, Kent: Butterworth; 1989.

5 Kilham H., Isaacs D. The New Children’s Hospital Handbook. Westmead: RAHC; 1999.

6 Apitz C., Webb G.D., Redington A.N. Tetralogy of Fallot. Lancet. 2009;374:1462-1471.

7 Allen H.D., Driscoll D.J., Shaddy R.E., et al. Moss and Adams’ heart disease in infants. children and adolescents: Including the fetus and young adult, 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2007.

8 Nichols D.G., Cameron D.E. Critical heart disease in infants and children, 2nd ed. Philadelphia: Mosby Elsevier; 2006.

9 Siwik E.S., Erenberg F., Zahka K.G., Goldmuntz E. Tetralogy of Fallot. In Allen H.D., Driscoll D.J., Shaddy R.E., et al, editors: 2007 Moss and Adams’ Heart Disease in Infants, Children and Adolescents: Including the Fetus and Young Adult, 7th ed., Philadelphia: Lippincott Williams & Wilkins, 2007.

10 Park M.K. Tetralogy of Fallot. In Park M.Y., editor: Pediatric cardiology for practitioners, 5th ed., Philadelphia: Mosby Elsevier, 2008.

11 van Roekens C.N., Zuckerberg A.L. Emergency management of hypercyanotic crises in tetralogy of Fallot. Ann Emerg Med. 1995;25(2):256-258.

12 Baele P.L., Rennotte M.T., Veyckemans F.A. External compression of the abdominal aorta reversing tetralogy of Fallot cyanotic crisis. Anaesthesiology. 1991;75(1):146-149.

13 Nussbaum J., Zane E.A., Thys D.M. Esmolol for the treatment of hypercyanotic spells in infants with tetralogy of Fallot. J Cardiothorac Anaesthesiol. 1989;3(2):200-202.

Further reading

Allen H.D., Driscoll D.J., Shaddy R.E., et al. Moss and Adams’ heart disease in infants, children and adolescents: Including the fetus and young adult, 7th ed., Philadelphia: Lippincott Williams & Wilkins, 2007.

Apitz C., Webb G.D., Redington A.N. Tetralogy of Fallot. Lancet. 2009;374:1462-1471.

Breitbart R.E., Fyler D.C. Tetralogy of Fallot. In Keane J., Fyler D., Lock J., editors: Nadas paediatric cardiology, 2nd ed., Philadelphia: Saunders Elsevier, 2006.

Nichols D.G., Cameron D.E. Critical heart disease in infants and children, 2nd ed, Philadelphia: Mosby Elsevier, 2006.

Park M.K. Congestive heart failure. In Park M.Y., editor: Pediatric cardiology for practitioners, 5th ed., Philadelphia: Mosby Elsevier, 2008.

van Roekens C.N., Zuckerberg A.L. Emergency management of hypercyanotic crises in tetralogy of Fallot. Ann Emerg Med. 1995;25(2):256-258.

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