The Fontan Procedure for Pediatric Tricuspid Atresia Workup

Updated: Mar 11, 2016
  • Author: Prema Ramaswamy, MD; Chief Editor: Jonah Odim, MD, PhD, MBA  more...
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Workup

Laboratory Studies

CBC count

Determine if the patient has concomitant iron deficiency anemia because this, in the presence of cyanosis and polycythemia, can increase the risk of a cerebrovascular accident in an infant.

Thrombocytopenia is not uncommon in an older child with cyanosis.

Test of prothrombin time and activated partial thromboplastin time

The results may be abnormal because of polycythemia.

Serum electrolytes and liver function tests

Results may be abnormal because of medical therapy administered to treat congestive heart failure.

ABG analysis

This is a critical test in a cyanotic newborn to confirm hypoxia.

Moreover, when this test is repeated after 100% oxygen is administered over 10 minutes, it helps in differentiating cardiac causes of cyanosis from the common pulmonary ones. In the former situation, the partial pressure of oxygen (PO2) does not exceed 150 torr because of the obligate right-to-left shunt. This has been termed the hyperoxia test.

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Imaging Studies

Chest radiography

Chest radiography is typically not helpful in diagnosing tricuspid atresia. In most patients, pulmonary vascular markings are diminished because of decreased pulmonary blood flow.

A right aortic arch is less common in tricuspid atresia than in tetralogy of Fallot, and it is seen in only 3-8% of patients. [7]

Electrocardiography

This is a useful test and helps narrow the differential diagnosis in a cyanotic newborn. The other 2 cyanotic heart diseases that are more common than tricuspid atresia (ie, tetralogy of Fallot and transposition of the great arteries), involve right ventricular hypertrophy. By contrast, tricuspid atresia involves left ventricular hypertrophy.

The typical ECG in tricuspid atresia demonstrates left ventricular hypertrophy and a superior left axis. Enlarged P waves suggestive of right atrial enlargement are also common.

Echocardiography

This is the primary modality for the diagnosis of tricuspid atresia. An echo-bright shelf is in the position the tricuspid valve normally occupies. Two-dimensional echocardiography can define the size and location of the chambers, great vessels, and the atrial and ventricular septal anatomy. Associated abnormalities, such as a left superior vena cava (SVC), juxtaposed atrial appendages, subaortic stenosis, and coarctation of the aorta, can also be well documented.

Blood-flow characteristics can be quantitated by using pulse and continuous-wave and color-flow Doppler methods. The pressure gradients across stenotic orifices, valves, and septal defects can be determined by using these techniques.

Fetal diagnosis is feasible and alters the outcome because of elective termination of a pregnancy. [14]

MRI

Although MRI is not used as ubiquitously as echocardiography in diagnosing tricuspid atresia, the advantages of MRI are improved delineation of extracardiac structures, such as the pulmonary artery anatomy, especially in older children.

Cardiac MRI might replace the role of cardiac catheterization before the stages of a Fontan surgery. [15]

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Diagnostic Procedures

In neonates, cardiac catheterization is almost never required any longer as echocardiography offers excellent details of the intracardiac anatomy. In rare cases, in the presence of a restrictive atrial septal defect it may be used to perform a balloon septostomy.

The current role of cardiac catheterization is primarily to assess the anatomy and the resistance of the pulmonary vascular bed before a bidirectional Glenn (or hemi-Fontan) operation, which is based on the similar principle of directing blood in the SVC to the pulmonary arteries. Catheterization is also performed before the modified Fontan procedure is completed. With improvements in cardiac MRI, even this role has been challenged as being unnecessary in most patients. [15]

In older children and adolescents, arteriography is used to define details important to surgical management, including the following:

  • Number and relationship of the vena cavae

  • Size of the pulmonary arteries

  • Pulmonary artery vascular resistance

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