Assessing the Newborn Circulation: What to Look Out For (4)

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Outflow obstruction in the healthy infant

Pulmonary stenosis
Most pulmonary stenoses are asymptomatic and are diagnosed clinically by an ejection systolic murmur at the upper left sternal edge. Patients with this condition should be followed-up in the clinic until balloon dilation is needed.

Aortic stenosis
Aortic stenosis is diagnosed by the presence of a murmur at the upper right sternal edge and is always accompanied by a thrill in the suprasternal notch. It may not be an isolated lesion and is often associated with mitral valve stenosis and coarctation of the aorta, the presence of which should always be excluded. Unfortunately, ECG and chest radiographs are diagnostically unhelpful in this age group.

Outflow obstruction in the sick infant
Lesions associated with outflow obstruction include coarctation of the aorta, hypoplastic left heart syndrome, critical aortic stenosis and interrupted aortic arch. Neonates presenting with these lesions after birth tend to be the most unwell of all those with duct-dependent systemic circulation; ductal constriction leads to profound acidosis and rapid cardiovascular collapse due to the low flow through the left side of the heart [10]. All peripheral pulses are weak, if not absent.

Children with outflow obstruction tend to present with heart failure and shock in the neonatal period (typically at 2 days of age, when the duct closes), but may present at any time from birth up to six weeks of age. The priority of management is resuscitation (ABC), followed by commencement of prostaglandin therapy at the earliest opportunity and immediate referral to a cardiac centre. In the case of neonates with obstructed totally anomalous pulmonary venous connection, whose presentation is similar to those with outflow obstruction, commencement of prostaglandin makes no difference (nor does it make them worse). Urgent and life-saving cardiac surgery is, however, essential.

Other congenital heart conditions

Cardiac arrhythmias: Supraventricular tachycardia
Supraventricular tachycardia is the most common childhood arrhythmia, with a rapid heart rate of between 250 and 300 beats/min and symptoms of heart failure in the neonate or young infant. Although structural heart problems are rare, an ECG should be performed nonetheless.

ECG readings generally show a narrow complex tachycardia of 250–300 beats/min, with a possible T-wave inversion in the lateral precordial leads when heart failure is severe; a short P-R interval may also be discernible in sinus rhythm. Early anterograde activation of the ventricle via the accessory electrical pathway results in a short P-R interval and a delta wave in the Wolff–Parkinson–White (WPW) syndrome.

Prompt restoration of sinus rhythm by ABC is the key to improvement in the severely ill neonate, followed by intravenous adenosine; this is safe and effective, inducing atrio-ventricular block after rapid bolus injection. If the baby has collapsed or adenosine fails, electrical cardio-version with a synchronised DC shock (1–2 J/kg body weight) may be needed. Maintenance therapy with flecainide or Sotalol is often required, although digoxin is not normally used.

Congenital complete heart block
Congenital complete heart block is a rare condition often related to the presence of anti-Ro or anti-La antibodies in the serum of mothers with either manifest or latent connective tissue disorders. Complications associated with the condition include fetal hydrops, death in utero and heart failure in the neonatal period. Subsequent pregnancies are also often affected. Although a few children with congenital complete heart block become symptomatic with pre-syncope or syncope, most remain symptom free for many years. The insertion of a pacemaker is essential in all symptomatic children.

Concluding remarks
In conclusion, the diagnosis and assessment of CHD in the neonatal period begins with a high index of clinical suspicion, a thorough history, examination and circulatory assessment. Examination of the neonate should ideally be performed after the successful transition from fetal to neonatal circulation by a clinician with experience in neonatal examination. Most life-threatening CHD in the neonatal period can be effectively managed with surgery. It is, therefore, essential to ensure that neonates with CHD are diagnosed before circulatory collapse occurs.


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