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2003-01-22-12 Coarctation of the aorta © Cormick www.thefetus.net/


Coarctation of the aorta

Wes Cormick FRACP, DDU

Canberra Imaging Group  ACT  Australia

Case report
The patient presented for a routine 18-week ultrasound with no known family history of congenital heart disease. 

The ultrasound demonstrated the following features with the fetal heart.

The 4-chamber view shows the right ventricle is larger than the left ventricle.


This is also shown in the transverse view of the ventricles.


The three-vessel view shows the pulmonary artery is large and the aorta is small.


Views of the right ventricular outflow showed the RVOT and ductal arch were diffusely enlarged with a normal Doppler waveform along them.


Views of the Left Ventricular outflow showed the LVOT was diffusely small with a normal Doppler waveform along it.

The atrioventricular valves had normal waveforms across them.

The foramen ovale was normal in size with a normal right to left waveform across it.

All vessels and chambers were otherwise normally connected and fetal size was consistent with dates.
 
The initial impression was that it might have been anomalous pulmonary venous drainage, but it was commented that a coarctation could not be excluded.
 
 
The study was repeated at  28 weeks gestation by a specialist fetal cardiologist which showed normal venous connections with persisting dilation of the right heart.  The child was delivered in good condition, with echocardiography showing a bicommissural aortic valve with mild aortic stenosis and a small isthmus with some angulation as it connected with a persisting patent ductus arteriosus.
 
Two days later a repeat echo showed a coarctation evolving as the ductus arteriosus became smaller. The child went on to have an end-to-end repair with a good outcome

Discussion:
Right heart enlargement may be due to a number of cardiac abnormalities, or occasionally non-cardiac abnormalities. The cardiac defects can be from the right heart, the left heart or both.  The right heart may have too much blood coming in to it (volume overload) or increased resistance to blood being pumped out of it (pressure overload). If there is impaired emptying of the left heart this will cause a volume overload of the right.


Approach to right heart enlargement

1) Right sided volume overload

1. Superior or inferior vena cava size may be increased in anomalous pulmonary venous return.

2. Pulmonary veins connected to right atrium in anomalous pulmonary venous return.

3. Examine the atrial and ventricular septum for a left to right shunt

4. Look for evidence of systemic volume overload:
        Hydrops, 
        Arterio-venous malformations e.g.:

                  Vein of Galen malformation,
                  Hemangioendothelioma,
                  Chorioangioma

2) Right sided pressure overload

1. Exclude a small foramen ovale by assessing its size and examining flow across it with color and Doppler. The foramen ovale is normally a similar size to the aortic valve throughout pregnancy and there is a biphasic right to left waveform with a peak velocity between 20 and 40 cm/second. There is restriction of flow if the size is less than 2mm or the peak velocity is greater than 100cm/sec.

2. Assess the flow across the tricuspid valve – the atrioventricular valves have a double spiked waveform with a peak velocity around 50 cm/second.

3. Assess the flow across the pulmonary valve – There is a single antegrade waveform in systole, which is normally around 60cm/sec.

4. Exclude narrowing of the ductus arteriosus by assessing its size and flow across it. Premature ductal constriction may be seen with maternal Indomethacin treatment. The size is normally about 90% of the aortic root and the peak velocity is abnormal if it is greater than 140cm/sec.

5. Placental insufficiency may cause right heart enlargement as the systemic arterial perfusion is predominantly supplied by the right ventricle via the ductus arteriosus. Placental abnormalities may cause elevated total peripheral resistance and pressure overload to the right heart. This is assessed by examining the biometry and the Doppler waveform in the umbilical artery.


3) Left sided outflow restriction

1. Assess the flow across the mitral valve and assess its size. The AV valves have a double spiked waveform with a peak velocity around 50 cm/second.

2. Assess the flow across the aortic valve. There is a single antegrade waveform in systole, which is normally around 70cm/sec.

3. Assess the flow along the aortic arch and assess its size. There may be focal or tubular narrowing giving an altered diameter and waveform.

4. Aortic outflow disorders may result in fibroelastosis, which demonstrate a thickened left ventricular wall.

5. NB:  Coarctation can not be excluded until after birth when the ductus arteriosus closes

6  May be normal in 3rd trimester: A number of pregnancies with enlarged right heart will demonstrate no abnormality on echocardiogram post birth

 

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