Assessment of Complex and Repaired Congenital Heart Disease

Tetralogy of Fallot

Tetralogy of Fallot is a common type of complex congenital heart disease. With an incidence of 0.1 per 1000 live births, it occurs in approximately 5.5% of all patients with congenital heart disease. The underlying abnormality is anterior displacement of the infundibular septum, which results in the three basic malformations that characterize this disorder:

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  Severe stenosis of the right ventricular outflow tract (RVOT)

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  An overriding aorta

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  Infundibular venticular septal defect (VSD)

The fourth element of the tetralogy is hypertrophy of the right ventricle, which occurs as a consequence of the three basic defects just cited.

Over the years, the surgical approach to this condition has changed. There has been a move from a staged approach in favor of a primary repair, with a progressive lowering of the age at repair and a surgical technique that avoids or reduces the need for a ventriculotomy.

The goals of surgical correction of tetralogy of Fallot are to relieve the RVOT obstruction and to close the underlying VSD.

The RVOT obstruction can be relieved in one of three ways:

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  Resection of a portion of the infundibular septum and other structures contributing to the outflow tract obstruction, such as prominent muscle bundles or muscular trabeculae

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  Enlarging the pulmonary outflow tract by placement of a transannular patch, which is constructed from prosthetic material or from autologous pericardium. This patch is applied to the anterior aspect of the RVOT.

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  Placement of an external conduit, usually involving a prosthetic pulmonary valve, between the right ventricle and the pulmonary trunk. This often is performed with a Dacron or Gore-Tex conduit and a bioprosthetic valve.

With all three methods, the VSD is closed with a patch of prosthetic material in such a way that the overriding aorta valve is exclusively committed to the left ventricular outflow tract.

Unfortunately, despite the improved surgical management, complications and residual sequelae after repair of tetralogy of Fallot are still common. Residual or recurrent VSD, RVOT obstruction or aneurysm formation, and pulmonary artery regurgitation and/or stenosis all lead to significant right ventricular dysfunction, resulting in significant morbidity and premature mortality.

MRI is currently the gold standard tool for postoperative evaluation of repaired tetralogy of Fallot. A number of patients, however, have relative contraindications to cardiac MRI, including pacemakers, claustrophobia, and underlying vascular stents, which can be difficult to image well due to susceptibility artifact.

Gated cardiac CT of postoperative tetralogy of Fallot patients allows:

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  Demonstration of residual anatomic problems:

  • Residual VSD if present

  • Pulmonary arterial stenosis (with or without stenting), which can be central or peripheral

  • RVOT aneurysm

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  Monitoring

  • Any underlying ascending aortopathy

  • Aortopulmonary collaterals

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  Quantification of right/left ventricular size and function

See Figures 25-1 through 25-3 ; Video 25-1.

Postsurgical Tetralogy of Fallot

Most patients with tetralogy of Fallot will have had surgery. Corrective surgery for tetralogy of Fallot can include the following procedures:

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  Placement of a ventricular septal patch, closing the high ventricular septal defect

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  Resection of RVOT/infundibular muscle bundles, which usually are the cause of RVOT obstruction

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  Pulmonic valvotomy. Pulmonic valve tissue often is dysplastic, thickened, and dysfunctional.

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  Placement of an RVOT patch, often in conjunction with RVOT muscle bundle resection to increase the volume of the RVOT

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  Transannular repair with placement of a transannular patch. This procedure is performed when the pulmonary valve annulus is small and restrictive. The surgery leaves the patient with free pulmonary insufficiency.

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  Pulmonic valve implantation. A porcine bioprosthesis or human homograft usually is chosen. These can be utilized in adults undergoing late repair, and in patients with prior pulmonary valvotomy/transannular patch placement who have developed severe RV dilatation.

In patients who have severe hypoplasia, or atresia of the RVOT, an extracardiac conduit can be placed. This usually extends from the RVOT or the body of the RV to a central pulmonary artery.

Most imaging follow-up for tetralogy of Fallot repair is done with echocardiography and cardiac MRI. In patients with contraindications to cardiac MRI, such as a pacemaker, or the patient’s inability to undergo an MRI study due to body habitus or claustrophobia, a CCT study can be of benefit.

While evaluation of pulmonic insufficiency and tricuspid insufficiency is, at best, limited with CT imaging, accurate morphologic evaluation of the right and left cardiac chambers, RV and LV volumes and ejection fractions, and central and peripheral pulmonary arterial anatomy can be obtained with high accuracy using a low-dose, dose-modulated helical acquisition. To assess the right ventricle as well as the left ventricle adequately on a CCT study, increased density of contrast is needed on the right side of the heart. This makes evaluation for intracardiac shunts such as an underlying patent foramen ovale or a VSD patch leak more challenging.

A CCT study for postoperative evaluation of a patient with tetralogy of Fallot repair would include the following:

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  Determination of RV end-diastolic volume (EDV), RV end-systolic volume (ESV), RV ejection fraction (RVEF)

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  Left ventricular EDV, left ventricular ESV, left ventricular EF

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  Evaluation of the intraventricular septum for patch integrity

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  Evaluation of the RVOT

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  Evaluation of the native or bioprosthetic pulmonary valve

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  Evaluation of an RV-to-PA conduit if one is present

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  Evaluation of central right and left pulmonary arteries

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  Evaluation of peripheral pulmonary arteries

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  Evaluation of the ascending aorta, which can become dilated in the setting of tetralogy of Fallot

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  See Figures 25-4 through 25-6 ; Video 25-2.

  
  
  

Transposition of the Great Vessels

Transposition of the great arteries (TGA) includes concordant atrioventricular connections and discordant ventriculoarterial connections. The aorta arises anterior to the pulmonary artery, from the morphologic right ventricle, and the main pulmonary artery arises from the morphologic left ventricle.

Before the arterial switch procedure was developed, patients with TGA required an atrial switch procedure such a Mustard or Senning procedure. This surgical correction creates an intra-atrial baffle separating systemic from pulmonary venous blood flow. The baffle redirects systemic blood from the inferior and superior venae cavae to the mitral valve and into the left ventricle. The pulmonary venous return is redirected to the tricuspid valve and the RV. The main difference between these two procedures is that the Mustard operation involves resection of atrial septal tissue in the formation of a baffle using either synthetic material, or autologous pericardium. The Senning procedure utilizes a baffle created from tissue from the right atrial wall and atrial septum, without the use of any extrinsic materials. In these procedures, however, the left ventricle remains the pulmonary ventricle, and the right ventricle the systemic ventricle. These operations usually were performed between the first month and first year of life.

MRI is the best modality to evaluate the integrity of the underlying surgical corrections, as well as to monitor the systemic right ventricle, which, in the long term, has a risk of failing. In patients with contraindications to MRI, evaluation of the postsurgical heart can be done using CCT.

Complications that can be assessed by cardiac CT include

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  Progressive RV (systemic ventricle) dilatation and dysfunction due to long-term pumping against systemic pressures

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  Evaluation of the superior and inferior baffles. The two major complications include baffle obstruction and baffle leak. Baffle stenoses are uncommon, but occur with greater frequency in the superior limb, with an incidence of 5% to 10% versus inferior limb obstruction, which occurs in only 1% to 2% of cases.

Baffle leaks may be present in up to 25% of patients, but most are small, and usually not hemodynamically significant. In patients with large baffle leaks, right-to-left shunting can occur, resulting in systemic arterial desaturation, requiring surgical or percutaneous closure.

Postsurgical Transposition of the Great Vessels