Neonatal cardiac emergencies

The neonatal period is one that fills many generalists with fear – this article will help to dispel these concerns.

George A Comitis, MB ChB, DCH (SA), DA (SA), FCPaed (SA), Cert Cardiology (SA) Paed

Consultant, Paediatric Cardiology Service of the Western Cape, Red Cross War Memorial Children’s Hospital, Cape Town, and Division of Critical Care and Children’s Heart Diseases, School of Child and Adolescent Health, University of Cape Town

George Comitis is the young blood of the paediatric cardiology team at Red Cross Children’s Hospital. He was lucky enough to be trained in the same unit after spending two wet years at the Royal Brompton Hospital as a Fellow in Paediatric Cardiac Intensive Care, during which he became tired of not being able to talk properly to his patients.

Correspondence to: G Comitis (gam.comitis@uct.ac.za)

Many congenital heart diseases (CHDs) present in the neonatal period. This article focuses on critical congenital heart defects with an incidence of 3 - 3.5/1 000 live births1 (almost half of all CHDs). These have been defined as lesions that are ‘duct dependent’ (i.e. dependent on a patent ductus arteriosus (PDA) for pulmonary or systemic blood flow) or require intervention (surgical or catheter) within the first month in order to sustain life or prevent major morbidity.2 In addition, common neonatal arrhythmias are discussed as these can also present as emergencies.

A clear appreciation of the pathophysiology of each particular CHD requires a sound understanding of the fetal, transitional and neonatal circulations, i.e. the normal physiological changes that occur after birth.

As detailed antenatal anomaly scanning is not routinely available in South Africa, the majority of neonates with critical CHD present clinically without a known diagnosis. Even when available, detection rates for CHD are modest, currently ranging from 57% to 67%.3 , 4 Despite the numerous different cardiac lesions, there is only a limited spectrum of clinical presentations that the practitioner is likely to encounter, i.e.:

• cyanosis

• shock

• tachyarrhythmias/bradyarrhythmias

• acute congestive heart failure.

This article discusses these presentations and provides practical acute management guidelines using clinical scenarios. Where overlap exists with conditions occurring in older infants and children, the reader is referred to the companion article ‘Common paediatric cardiac emergencies’ in this journal for further details.

Cyanosis

A detailed description of cyanotic CHD is beyond the scope of this article. Rather, a few pointers are given to assist in distinguishing between respiratory and cardiac causes of cyanosis in the neonate (Table I), as the former represents the main differential diagnosis, with mention of the more common lesions. Thereafter essential emergency care is discussed.

It is useful to remember the most common cyanotic CHDs as the 5 Ts: in order of frequency – tetralogy of Fallot (and pulmonary atresia), transposition of great arteries, tricuspid atresia, TAPVD, and truncus arteriosus. In addition, an important differential is persistent pulmonary hypertension of the newborn (PPHN) – suggestive features would be a history of risk factors for PPHN (such as perinatal asphyxia or meconium aspiration) and differential cyanosis, i.e. oxygen saturation/pO2 in the feet (postductal) lower than the right hand (preductal) due to R to L shunting across the PDA. NB: This is also a feature of critical aortic arch obstructions (see below).

In the introductory scenario, the baby probably has an RV outflow tract obstructive lesion (extreme tetralogy, critical pulmonary stenosis or atresia), i.e. duct-dependent pulmonary circulation, and was relatively well until spontaneous closure of the PDA on day 2 caused acute hypoxaemia and acidosis. The patient requires resuscitation as follows:

Management

• Open the PDA ASAP! Mainstay therapy for reopening a PDA and keeping it open is prostaglandin E1 (alprostadil) IV infusion (starting dose 50 - 100 ng/kg/min, if poor response (saturations and acidosis not improving) increase to max 300 - 400 ng/kg/min, maintenance dose 10 - 25 ng/kg/min) or prostaglandin E2 (dinoprostone) orally/via nasogastric tube (dose 25 μg/kg or quarter tablet (500 μg strength) every ½ - 1 hour) – the latter should be available at all hospitals as an emergency drug, the former usually only at referral centres. Oral PGE2 is very safe (baby unlikely to come to any harm if diagnosis is not cyanotic CHD), but IV PGE1 can cause apnoea/hypoventilation and hypotension; hence used more in ICU or high-care settings. Prostaglandins may be used to attempt reopening of a PDA in a neonate up to 30 days of age.

• Blood volume expansion – 10 ml/kg 0.9% saline IV bolus, repeat as needed until liver edge palpable – to improve preload and hence encourage further opening of the PDA and pulmonary blood flow through the duct.

• Sodium bicarbonate empirically (as acidosis aggravates hypoxic pulmonary vasoconstriction) – 1 mmol/kg IV as a 4.2% solution, repeat according to blood gas.

• Correct other derangements, e.g. hypoglycaemia, hypocalcaemia, con-comitant sepsis.

• Oxygen administration – aiming for saturations 75 - 85% (depending on exact diagnosis).

• Inotropes/vasopressors may be indicated to maintain adequate systemic perfusion and encourage pulmonary perfusion (by increasing systemic vascular resistance).

• If poor response to above, intubation/ventilation with sedation +/- paralysis to minimise metabolic demands and improve oxygenation.

• Consult with paediatric cardiologist and, once stabilised, transfer to tertiary centre for definitive diagnosis (usually with echocardiography) and management – this may entail cardiac catheterisation and often palliative surgery (e.g. modified Blalock-Taussig shunt).

Shock

The practitioner faced with a shocked neonate needs to have a high index of suspicion for CHD as the presentation can often be mistaken for neonatal sepsis. The usual lesions implicated are the critical left-sided outflow tract obstructions such as critical aortic stenosis (AS), hypoplastic left heart syndrome (HLHS), critical coarctation and interrupted aortic arch, which all represent duct-dependent systemic circulations. These are also the most commonly missed critical CHD diagnoses.5 In critical AS and HLHS the R to L PDA flow provides all the systemic perfusion and in the arch obstructions provides flow to the lower body causing differential cyanosis (pink arms, blue feet). However, this sign is less prominent or absent if there is intracardiac mixing of systemic and pulmonary venous blood (e.g. coexistent large ASD or VSD).

Important, and often missed (suggesting an arch obstruction), are discrepant pulses (as in the above scenario) and blood pressure (lower limb blood pressure less than that of upper limb, or even undetectable). Radio-femoral delay is impossible to detect at the fast heart rates of neonates – rather examine for diminished volume or absent pulses. The above neonate likely has a critical aortic arch obstruction with acute loss of lower body perfusion causing shock and metabolic acidosis after spontaneous ductal closure on day 5 - 6 (preserved brain perfusion, hence alert). He needs resuscitation as follows:

Management

• Arrange urgent admission to ICU and do not delay treatment.

• Again – open the PDA ASAP! Prostaglandin therapy as above for duct-dependent pulmonary circulation. Note that oral PGE2 may be less reliable as gut absorption may be compromised in this setting. However, oral PGE2 must be started if IV PGE1 is not available.

• Blood volume expansion – 0.9% saline in 5 - 10 ml/kg aliquots, monitoring liver size, to assist opening the PDA and improving systemic perfusion (baby also likely to be hypovolaemic with poor feeding and vomiting).

• The rest of the resuscitation and stabilisation would be similar to the above approach for cyanosis, e.g. inotropes (especially if coexistent LV dysfunction), oxygen to achieve preductal saturations (>85% in this case), and often mechanical ventilation.

• It is important to check for and manage end-organ damage such as renal failure, liver dysfunction and gut ischaemia/necrotising enterocolitis as per routine ICU protocols.

• Transfer to tertiary centre for definitive management – confirmation of diagnosis by echocardiography and, usually, primary surgical repair of the arch obstruction.

Tachyarrhythmias

A 1-day-old neonate is referred to you soon after birth with a heart rate of 280/min. He was delivered by caesarean section for fetal tachycardia but had good Apgar scores and there were no risk factors for congenital sepsis. He is alert, comfortable in room air and perfusing well without signs of cardiac failure. What is the differential diagnosis?

The most common neonatal tachyar-rhythmias (excluding sinus tachycardia which usually does not exceed 220/min) are atrioventricular re-entry tachycardia (AVRT) (associated with an accessory AV pathway) followed by atrial flutter. Less likely causes include AV node re-entry tachycardia, ectopic and multifocal atrial tachycardia and junctional tachycardias. Note that these are all narrow QRS complex tachycardias. Wide complex tachycardias are less commonly seen and, as for older children, merit urgent consultation with a paediatric cardiologist. They are best regarded and treated as ventricular tachycardia rather than SVTs with aberrant conduction.

You decide to administer adenosine. This has only a very transient effect slowing the rate to about 130/min – after a few seconds the rate is again 280/min. Fig. 1 shows the rhythm strip you recorded during adenosine administration. What is the likely diagnosis and how will you treat it?

Fig. 1 shows the typical ‘saw tooth’ baseline of atrial flutter, more manifest after adenosine, which slows the ventricular rate.

Management

• Atrial flutter: adenosine is not effective. The treatment of choice is synchronised DC cardioversion – as little as 0.5 J/kg is often enough to cardiovert to sinus rhythm. Ensure that paediatric paddles are used with adequate electrode jelly and the correct application front and back of the chest for a neonate. Remember to sedate the baby for comfort.

• AVRT: similar approach as for older children – if shocked, initial attempt at vagal manoeuvre and, if unsuccessful, progress immediately to synchronised DC cardioversion 1 J/kg, then 2 J/kg if no response or adenosine, whichever is quicker to administer. The starting dose of adenosine for neonates is 150 μg/kg rapid IV bolus; if no response, increase by 50 μg/kg every 2 minutes to a maximum single dose of 300 μg/kg.

• Wide complex tachycardia (probable VT): synchronised DC cardioversion 1 J/kg, then 2 J/kg if no response (sedate if conscious without delaying cardioversion).

• Treat any aggravating and reversible factors, e.g. hypoglycaemia, electrolyte imbalance, acidosis.

• It is good practice to record the tachyarrythmia on a 12-lead ECG as well as a rhythm strip before and during any therapy (cardioversion or adenosine as in the above case) so that the rhythm can be analysed by a cardiologist.

• If still no response, consult a paediatric cardiologist and refer to a tertiary centre (options include amiodarone, digoxin or propranolol, depending on the diagnosis).

Bradyarrhythmias

A baby is delivered at term by caesarean section for presumed ‘fetal distress’ (fetal bradycardia noted on cardiotocogram (CTG). You attend the delivery and note that the baby is vigorous at birth but remains bradycardic at 48/min. Her ECG is shown in Fig. 2. What is the diagnosis?

The commonest cause of bradycardia in the neonate (defined as a heart rate <70/min) is congenital complete heart block (CHB). Fig. 2 is a typical example showing atrioventricular dissociation and a narrow QRS escape. It is often associated with maternal lupus erythematosus or other connective tissue diseases (which are often asymptomatic in the mother). Less commonly, cases may be isolated or associated with CHD.

Acute management

• The majority of neonates (with heart rates above 50 - 55 bpm) will be asymptomatic with good cardiac output and hence will not require immediate treatment – they may be referred, on the same admission, to a paediatric cardiologist for exclusion of structural heart disease and ongoing observation.

• If the neonate is symptomatic (signs of heart failure or cardiogenic shock), treat as for the older child – positive chronotropes (atropine, adrenaline or isoprenaline), blood volume expansion and temporary pacing under sedation (transcutaneous or transoesophageal) – see accompanying article ‘Common paediatric cardiac emergencies’ in this issue.

• Eventually all patients will require permanent cardiac pacing but this can often be delayed for years in the stable patient.

Acute congestive heart failure

Many of the critical CHDs as well as the arrhythmias discussed in this article can present with acute heart failure (HF). The important point is to differentiate HF from respiratory distress due to lung disease or neonatal sepsis – as in older children, useful clues for HF are cardiomegaly and hepatomegaly.

Management

• Non-pharmacological measures, e.g. fluid restriction, nutritional support, oxygen and ventilatory support as indicated, correct aggravating factors such as anaemia or sepsis.

• Diuretics, usually furosemide 0.5 - 1 mg/kg 8 - 12-hourly IV or orally with spironolactone 1 mg/kg 12-hourly per mouth.

• ACE inhibitors are generally contraindicated in neonates (high risk of severe hypotension and renal failure).

• Inotropes/vasodilators such as dobutamine may be indicated in severe HF.

• Refer to tertiary paediatric cardiac centre (on the same admission) for definitive management. The above-described neonate is found to have truncus arteriosus and proceeds to full surgical repair after 5 days of stabilisation on anti-failure treatment as above.

Conclusion

The practitioner faced with an acutely ill neonate needs to have a high index of suspicion for a cardiac aetiology. Obvious clues would include all of the above presentations. A thorough cardiovascular examination should always be undertaken – without delaying emergency care – including a hyperoxia test in the cyanosed neonate, a check for discrepant pulses and blood pressures, and differential cyanosis. A chest X-ray and 12-lead ECG are essential first-line investigations to narrow the differential diagnosis. Immediate stabilisation as outlined above, followed by prompt referral to a tertiary centre, provides the best opportunity to minimise morbidity and mortality.

References

1. Vetter VL. Pediatric Cardiology – The Requisites in Pediatrics. Philadelphia: Elsevier Mosby, 2006.

2. Liske MR, et al. Report of the Tennessee Task Force on Screening Newborn Infants for Critical Congenital Heart Disease. Pediatrics 2006;118(4):e1250-e1256.

3. Levey A. The impact of prenatal diagnosis of complex congenital heart disease on neonatal outcomes. Pediatr Cardiol 2010;31(5):587-597.

4. Tegnander E, et al. Prenatal detection of heart defects in a non-selected population of 30149 fetuses – detection rates and outcome. Ultrasound Obstet Gynecol 2006;27:252-265.

5. Chang R-K, et al. Missed diagnosis of critical congenital heart disease. Arch Pediatr Adolesc Med 2008;162(10):969-974.

Bibliography/suggested further reading

Advanced Life Support Group. Advanced Paediatric Life Support – The Practical Approach. 5th ed. London: BMJ Publishing Group (Wiley Blackwell), 2010.

Park MK. Pediatric Cardiology for Practitioners. 5th ed. Philadelphia: Mosby Elsevier, 2008.

Park MK. The Pediatric Cardiology Handbook. 4th ed. Philadelphia: Mosby Elsevier, 2010.

Vetter VL. Critical heart disease in the newborn (ch. 2). In: Vetter VL, ed. Pediatric Cardiology – The Requisites. Philadelphia: Mosby Elsevier, 2006.

 

Fig. 2. Neonate with bradycardia.