Differentials
Other cyanotic congenital cardiac abnormalities
SIGNS / SYMPTOMS
Includes single ventricle lesions such as hypoplastic left heart syndrome or tricuspid atresia. Other possibilities include D-transposition, pulmonary atresia, anomalous pulmonary venous connection, truncus arteriosus, or Ebstein's anomaly.
These may all be difficult to differentiate clinically from a cyanotic newborn with TOF. Most are not specifically associated with other syndromes, although this can vary.
INVESTIGATIONS
No change in PaO2 with hyperoxia test.
Echocardiogram can define anatomy to classify cyanotic heart disease.
In some cases, a cardiac catheterisation may be needed to further define anatomy and physiology.
Pulmonary stenosis
SIGNS / SYMPTOMS
Usually presents in an asymptomatic patient with a systolic ejection murmur on examination. Difficult to differentiate clinically from TOF.[23]
INVESTIGATIONS
Echocardiogram will show presence or absence of typical anatomy of TOF with pulmonary obstruction to differentiate from pulmonary stenosis alone.
Ventricular septal defect (VSD)
SIGNS / SYMPTOMS
At birth, an infant with simple VSD is fully saturated with regurgitant murmur on examination.
Intensity of murmur depends on size of VSD and flow across the VSD. A small VSD has a louder murmur because the gradient between the right and left ventricles is higher. A large VSD has a soft murmur because pressures are equalised between the right and left ventricles.
As pulmonary vascular resistance drops, more blood shunts from left to right across the VSD and may result in pulmonary over-circulation and heart failure. This is uncommon with TOF, as the pulmonary obstruction prevents over-circulation.
INVESTIGATIONS
Echocardiogram will show presence or absence of right-sided obstructive lesion to determine whether this is VSD alone or TOF.
Double outlet right ventricle with normally related great vessels and pulmonary stenosis
SIGNS / SYMPTOMS
Cannot be differentiated from TOF on physical examination alone.
INVESTIGATIONS
Echocardiogram will show presence or absence of subaortic conus and degree of aorta over-ride of the VSD to differentiate TOF from double outlet right ventricle.
Primary pulmonary disease
SIGNS / SYMPTOMS
On examination, infant may be tachypnoeic and desaturated, potentially requiring mechanical ventilation.
Cardiovascular examination is usually normal.
INVESTIGATIONS
Hyper-oxygenation test should show increase in PaO2 with administration of 100% FiO2.
CXR will show normal cardiac silhouette with increased lung markings.
Echocardiogram will show normal intracardiac anatomy.
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