Tetralogy of Fallot With Absent Pulmonary Valve Workup

Updated: Nov 22, 2015
  • Author: Prema Ramaswamy, MD; Chief Editor: Howard S Weber, MD, FSCAI  more...
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Workup

Approach Considerations

Tetralogy of Fallot (TOF) with absent pulmonary valve can be accurately diagnosed based on fetal echocardiography findings. Galindo et al reported that many fetuses with absent pulmonary valve syndrome have an increased nuchal thickness in the first trimester; this may help with earlier recognition of the defect. [5] They also found the 22q11 microdeletion to be the most common associated karyotype anomaly, which was present in 21% of their patients. [5]

A report on the utility of fetal MRI in a fetus with TOF with absent pulmonary valve documents its ability not only to assess the size of the pulmonary arteries, but also the symmetry of the aeration of the lungs secondary to obstruction and over inflation. In addition, the volume of the lungs can be determined. All these factors can then allow better anticipation of the patient's postnatal management, including the use of extracorporeal mechanical ventilation and early surgery. [19]

Obtain a hemogram (complete blood cell [CBC] count) to determine hemoglobin and hematocrit levels. In addition, an arterial blood gas (ABG) study can provide useful information in a sick infant.  The use of pulse oximetry on any extremity will indicate the severity of the pulmonary outflow tract obstruction and the need for supplemental oxygen or additional intervention. 

Electrocardiography (ECG) demonstrates the presence of right ventricular hypertrophy (RVH) and greater left ventricular (LV) forces than typical for TOF (some show actual LV enlargement). Right atrial enlargement may also be present.

A study suggests that preoperative pulmonary function testing (PFT) in patients with TOF with absent pulmonary valve may help clinicians manage mechanical ventilation in these patients. [20] Markedly elevated airway resistance as well as flow limitation in medium to small airways with a mild reduction of forced vital capacity were noted. In postoperative patients evaluated with varying levels of positive end expiratory pressure (PEEP), there was improvement in tidal volume and reduced obstruction with PEEP greater than 10 cm H2O. [20]

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Radiologic Studies

Radiography, echocardiography, and magnetic resonance imaging (MRI) are imaging modalities that have been used in the evaluation of tetralogy of Fallot (TOF) with absent pulmonary valve.

Chest radiography

Chest radiography usually reveals aneurysmally dilated central pulmonary arteries with otherwise normal peripheral pulmonary vascularity. Cardiomegaly results from dilation of the right ventricle (RV), particularly its outflow tract (infundibulum).

Other pulmonary parenchymal abnormalities may be evident (eg, atelectasis, pneumonic infiltrate, lobar emphysema, hyperinflation). The air trapping may cause a herniation of a lobe.

A right aortic arch may be found in some patients.

Echocardiography

Echocardiography is usually diagnostic in this condition. Findings similar to those of tetralogy of Fallot include the characteristic large ventricular septal defect (VSD), enlarged anteriorly displaced aorta, and RV hypertrophy.

The conal septum is displaced anteriorly, but the RV infundibulum is patent and may be dilated if the degree of pulmonic regurgitation is substantial.

The pulmonary annulus demonstrates some degree of hypoplasia, and pulmonary valve leaflets are not observed.

The pulmonic trunk (main pulmonary artery) and proximal right and left pulmonary arteries are dilated in proportion to the degree of pulmonic regurgitation. This is also true for the RV, which is enlarged and demonstrates paradoxical septal motion.

Four key echocardiographic features of absent pulmonary valve syndrome that appear to differentiate it from tetralogy of Fallot are as follows [21] :

  • Absence of pulmonary valve or presence of pulmonary valve dysplasia
  • Concurrent stenosis and regurgitation at the pulmonary annulus
  • Significant aneurysmal dilatation in the areas of the pulmonary arteries
  • Increased rather than decreased pulmonary artery pressure

Doppler echocardiography

Doppler echocardiography demonstrates turbulence through the RV outflow tract. Pulmonary regurgitation is readily identified, but the ductus arteriosus is rare. Flow across the VSD is not turbulent, because the defect is large and unrestrictive and is generally bidirectional.

Magnetic resonance imaging

An MRI may be used to obtain the above information and has the added advantage of lack of radiation exposure.

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Cardiac Catheterization and Angiography

Echocardiography in the typical patient provides all of the information necessary to plan surgical repair. Unusual anatomy or the presence of some complicating additional defects rarely requires the need to perform catheterization in order to plan surgical intervention.

Abnormal pulmonary artery distribution and branching with possible peripheral pulmonary stenosis may be identified.

Catheterization may be appropriate in patients with absence of the left pulmonary artery or origin of a pulmonary artery directly from the aorta.

Right ventricular angiography demonstrates the stenotic pulmonic annulus with the dilated right and left pulmonary arteries. This has been called the "Mickey Mouse" appearance.

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