Conotruncal Lesions

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7 Conotruncal Lesions

Amy H. Schultz

Tetralogy of Fallot

Background

• The four historically described features of tetralogy of Fallot (TOF) are ventricular septal defect (VSD), overriding aorta (Ao), pulmonary stenosis (PS), and right ventricular hypertrophy (RVH) (Fig. 7-1).
• However, it is better for the echocardiographer to understand the key features:

• Large VSD of the anterior malalignment type (the conal or infundibular portion of the ventricular septum [VS] is anteriorly displaced).
• Underdevelopment of the right ventricular outflow (RVO), which can lead to obstruction at the subvalvar, valvar, and supravalvar levels.
• The aortic override and RVH can be thought of as secondary consequences to these features.

• A continuum of severity exists.

• “Pink tets” have little in the way of PS, exclusively left-to-right shunting and physiology more akin to a large VSD.
• The typical patient with TOF has an intermediate degree of obstruction, which usually progresses with time.
• Toward the severe end of the spectrum, there may be critical degrees of obstruction, requiring ductal patency for adequate oxygenation.
• In the extreme, there is pulmonary atresia. There may be no identifiable central pulmonary arteries (PAs); the lungs are supplied by multiple collateral vessels, termed major aortopulmonary collaterals (MAPCAs). This anatomy is also termed pulmonary atresia/VSD, distinguishing it from pulmonary atresia with an intact VS.

• A notable variant is TOF with absent pulmonary valve (pulmV) syndrome.

• The pulmonary valve leaflets are vestigial. In utero, there is free pulmonary insufficiency (PI) and usually a relatively mild degree of stenosis.
• The ductus arteriosus is usually absent.
• The branch PAs are often severely dilated and may compress the airways, leading to severe respiratory distress at birth.
• A typical TOF repair involves closing the VSD to provide unobstructed outflow from the left ventricle (LV) to the aorta and relief of all levels of pulmonary valve stenosis, often using a transannular patch.
• Coronary artery anatomy must be clearly defined before placement of a transannular patch to ensure that no important coronary artery crosses the right ventricular outflow tract (RVOT).

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Figure 7-1 Schematic depicting the anatomy of tetralogy of Fallot (TOF).

Overview of Echocardiographic Approach

• Cardiac segmental connections are normal (two dimensional [2D]).
• Demonstrate the anterior malalignment of the conal septum and the various levels of RVOT obstruction (2D, color Doppler, pulsed wave [PW] Doppler, and continuous wave [CW] Doppler).
• Demonstrate the branch PAs (or lack thereof if not present) (2D, color Doppler).
• Evaluate for DA (2D, color Doppler, PW Doppler, CW Doppler).
• Evaluate for additional VSDs (2D, color Doppler).
• Evaluate coronary artery anatomy (2D, color Doppler).
• Evaluate arch branching pattern; right aortic arch is present in approximately 25% (2D, color Doppler).

Anatomic Imaging

Acquisition

• Transthoracic echocardiography (TTE) is used to establish the diagnosis in neonates.
• Transesophageal echocardiography (TEE) may be used pre- and postoperatively.
• Beginning with the subcostal views, evaluate the segmental anatomy.

• Perform careful 2D sweeps in the frontal (long axis) and bicaval (sagittal) planes, noting the morphology and relationship of structures. The segmental anatomy is normal (see Chapter 1, The Pediatric Transthoracic Echocardiogram).
• In addition, perform a true subcostal short axis (45 degrees between the frontal and bicaval planes) 2D sweep from base to apex. This can be particularly helpful in visualizing:

• Atrial septal defect (ASD).
• Ventricular morphology.
• Malalignment VSD (the anterior malalignment of the conal septum is well seen).
• Any additional muscular VSDs.
• Mitral-aortic fibrous continuity (if no continuity, consider the diagnosis of double-outlet right ventricle [DORV]).
• RVOT.

• A right oblique view can be obtained by rotating 90 degrees counterclockwise from the short axis view and angling the beam of sound toward the right shoulder. This provides good views of the anterior malalignment VSD and RVOT (Fig. 7-2).

• Apical views

• Ensure that both ventricles have normal size and function.
• In the five-chamber view, the main VSD is apparent.
• Assess for any additional muscular VSDs.

• Parasternal long axis view (Fig. 7-3)

• Note mitral-aortic fibrous continuity. If not present, consider the diagnosis of DORV.
• Note the override of the aortic valve (AV).
• Optimize image of pulmonary valve for annular measurement.
• Parasternal short axis view (Fig. 7-4)

• Note the anterior malalignment of the conal septum and the large VSD.
• Note any evidence of RVOTO, pulmonary valve hypoplasia/stenosis, supravalvar stenosis, and branch PA stenosis.

• In TOF/absent valve, the main PA and branch PAs will be dilated (Fig. 7-5).
• In TOF with pulmonary atresia, the main PA (Fig. 7-6) or central PAs may be absent.

• Carefully image the coronary arteries (Figs. 7-7 and 7-8). In particular, demonstrate the origin and course of the anterior descending coronary and rule out any coronary artery crossing the pulmonary outflow tract. A significant coronary artery crossing the pulmonary outflow tract precludes a transannular patch. Decreasing the dynamic range and appropriate adjustment of focal zone and zoom features facilitates visualization.
• Short axis sweeps of the ventricles are used to evaluate function and any additional VSDs. Additional muscular VSDs may be difficult to detect by color Doppler imaging in the presence of another large VSD; thus, careful attention to the 2D images is mandatory.
• High parasternal short axis images, rotated slightly counterclockwise, may be used to image a patent ductus arteriosus (PDA).
• Suprasternal notch imaging

• Demonstrate arch sidedness and branching from the suprasternal short axis view. A right aortic arch occurs in about 25%. Some types of right aortic arch constitute a vascular ring. (See Chapter 1, The Pediatric Transthoracic Echocardiogram, for technique.)
• Branch PAs may be well seen from suprasternal notch short axis view.
• With variants of TOF with more significant obstruction, the ductus may be tortuous and originate from the underside of the arch. This is best seen with the sagittal view of the arch.

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Figure 7-2 Subcostal right oblique views of the right ventricular outflow tract (RVOT) in TOF. A, Two-dimensional (2D) image shows the anteriorly malaligned conal septum and the resultant VSD. The RVOT is somewhat narrowed by the deviated conal septum.B, The addition of color Doppler shows aliasing of flow in the RVOT. C, Pulsed wave Doppler in the RVOT shows only mild acceleration of flow in the RVOT. There is a slightly late-peaking waveform, consistent with dynamic obstruction. In this patient, the obstruction was predominantly higher up, at the valve level.

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Figure 7-3 Parasternal long axis view of unrepaired TOF: the aorta (Ao) is seen overriding the ventricular septal defect (VSD); fibrous continuity between the aortic valve (AV) and mitral valve (MV) is noted.

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Figure 7-4 Parasternal short axis view of unrepaired TOF: the anteriorly malaligned conal septum is well seen, leaving a large VSD. The RVOT is narrowed, and the pulmonary valve (pulmV) is hypoplastic. A restricted jet of color flow passes through the pulmonary valve, which in this case was unicuspid.

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Figure 7-5 Parasternal short axis view of the pulmonary valve and proximal PAs in TOF with absent pulmonary valve syndrome. The hypoplastic pulmonary valve annulus with vestigial pulmonary valve leaflets is seen. The proximal right pulmonary artery (RPA) is massively dilated; the origin of the dilated left pulmonary artery (LPA) is seen.

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Figure 7-6 Parasternal short axis view of the PAs in TOF with pulmonary atresia. In this case, the central PAs are confluent, but there is no main PA segment. The color panel shows the entry of the ductus (red) into the confluence of the branches.

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Figure 7-7 Parasternal short axis 2D image showing a normal course of the left anterior descending coronary artery. In this case (not shown), the right coronary artery was also shown to be normal, with no significant branch crossing the RVOT. Color confirmation of the coronary courses is also recommended (not shown).

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Figure 7-8 Coronary artery patterns observed in TOF. Frequency of occurrence is shown in the lower left-hand corner of each box. Note that approximately 94% of cases of TOF have one of the two “normal” patterns. Although more complex patterns are rare, they are critical to recognize because they preclude indiscriminate transannular patch. Conduit placement or careful, limited transannular incisions are required for repair.

(From Need LR, et al. Coronary echocardiography in tetralogy of Fallot: diagnostic accuracy, resource utilization and surgical implications over 13 years. J Am Coll Cardiol. 2000;36:1371–1377.)

Analysis

• Measure ASD/patent foramen ovale (PFO) from the subcostal 2D views.
• Measure the malalignment VSD from the parasternal short axis 2D view and another orthogonal view (apical or subcostal).
• Measure any additional VSD in the view in which it is best seen.
• Measure the pulmonary valve annulus, main PA, and branch PAs from the parasternal views. Compare with norms based on body surface area (BSA) (Z scores).
• Measure the PDA at its narrowest point in the view in which it is best seen.

Pitfalls

• In TOF with pulmonary atresia with no central PAs, the left atrial appendage (LAA) can be mistaken for the main PA. Avoid this pitfall by careful attention to the 2D images and use of color Doppler. The LAA will have a to-and-fro flow pattern in it.

Physiologic Data

• Doppler techniques are used to:

• Assess size, location, and direction of shunting of ASDs and VSDs.
• Evaluate PDA.
• Assess RVOTO and PA stenosis.
• Further visualize coronary arteries.

• Subcostal views

• Perform color sweeps of the atrial septum (AS) and VS. Be alert for any additional muscular VSDs, which may be difficult to visualize because the ventricular pressures are typically equal due to the large primary VSD. Determine the direction and velocity of shunting across shunts. Generally, VSDs will be unrestrictive.
• Evaluate RVOT from the subcostal short axis view.

• This view provides good Doppler alignment for spectral analysis in the subvalvar and valvar region.
• Perform a careful PW analysis, starting within the right ventricle (RV) below any muscle bundles evident on 2D imaging, marching up through the RVOT and pulmonary valve. Use the 2D image to guide your placement of the Doppler cursor, thus demonstrating the significance of obstruction at the various levels.
• Use CW Doppler to determine the highest velocity.

• Apical views

• Assess tricuspid valve (TV) and mitral valve (MV) function with color Doppler. Note that obtaining a right ventricular (RV) pressure estimate is irrelevant in the presence of a large VSD. The RV pressure is equal to the left ventricular (LV) pressure.
• Evaluate the apical muscular septum with color Doppler for additional VSDs.

• Parasternal views

• Assess valve function with color Doppler.
• Assess outflow tract obstruction with color Doppler and spectral Doppler. In particular, pulmonary outflow obstruction may be assessed from the parasternal short axis. Use careful PW Doppler to localize various levels of obstruction. Use CW Doppler to assess highest velocity.
• Evaluate the muscular septum with color Doppler for additional VSDs.
• Use color Doppler with very low Nyquist limit to assess flow in coronary arteries. Confirm that direction of flow is consistent with your understanding of the 2D anatomy. If not, reevaluate 2D anatomy.
• Evaluate for PDA with color Doppler from high parasternal window as described previously. If present, demonstrate velocity and direction of shunting by spectral Doppler.

• Suprasternal sagittal views

• Evaluate for PDA by color Doppler. If a ductus is present, demonstrate velocity and direction of shunting by spectral Doppler.
• In TOF with pulmonary atresia, examine the course of the arch and thoracic aorta with color Doppler to identify collaterals.

Alternate Approaches

• Cardiac catheterization with angiography is used:

• To definitively determine coronary artery anatomy if there is concern about an abnormal pattern or if the coronary arteries were inadequately imaged.
• In all cases of TOF with pulmonary atresia with MAPCAs to determine the number, size, and location of collaterals and to define which segment(s) of the lung is perfused by each collateral.

Key Points

• Key anatomic features

• Large VSD of the anterior malalignment type.
• Underdevelopment of the pulmonary outflow, which can lead to obstruction at the subvalvar, valvar, and supravalvar levels.
• The aortic override and RVH can be thought of as secondary consequences to these features.

• Key aspects of the preoperative echocardiogram

• Define the location and severity of the levels of pulmonary outflow obstruction.
• Evaluate for any coronary artery crossing the RVOT (present in ~5% of cases) that would preclude a transannular patch repair.
• Evaluate for additional VSD and PDA.
• Evaluate arch sidedness and branching pattern.

• Notable anatomic variants include the following:

• TOF with pulmonary atresia (also known as pulmonary atresia/VSD). In the most severe cases, there may be no identifiable central PAs, and the lung fields are supplied by MAPCAs.
• TOF with absent pulmonary valve: main PA and branch PAs are typically severely dilated and may cause airway compression; the ductus is usually absent.

TOF Repaired

Background

• Repair of TOF entails the following:

• Patch closure of the VSD.
• Establishment of unobstructed outflow from the RV to the PAs, tailored to the anatomy of the individual patient.

• In the best case, the pulmonary valve annulus is of adequate size and RV muscle bundles can be resected through the TV and pulmonary valve, avoiding right ventriculotomy (transatrial/transpulmonary repair).
• More frequently, the pulmonary valve annulus is hypoplastic, and a transannular patch is required. The surgeon incises from the main PA, across the pulmonary valve and onto the RV and then augments the area with a patch. Free PI results.
• If a coronary artery crosses the RVOT or if there is pulmonary atresia with no continuity of the main PA to the RV, then an RV-to-PA conduit is placed.
• If pulmonary blood flow (PBF) is via MAPCAs, the collaterals must first be brought together (unifocalized) before the conduit is placed. In this case, often the VSD is not closed at the first operation.

• Closure of any large ASD. A PFO is frequently left open to facilitate maintenance of cardiac output in the immediate postoperative period.

• The most important long-term follow-up issue in TOF is the development of RV dilation and dysfunction due to chronic PI and previous ventriculotomy. Serial evaluation of RV size and function is key.
• Branch PA stenosis can be an important issue after TOF repair.
• Aortic root enlargement and aortic insufficiency are observed late after TOF repair.

Overview of Echocardiographic Approach

• Review the history if possible before beginning the study to understand what type of repair was performed.
• Evaluate for residual ASD or VSD (2D, color Doppler, PW Doppler, CW Doppler).
• Evaluate the outflow from the RV to PAs (2D, color Doppler, PW Doppler, CW Doppler).

• Residual obstruction can occur at any level. Use PW Doppler to localize any area of obstruction.
• Free PI is often present (color Doppler, PW Doppler).
• Evaluate for branch PA stenosis (more commonly left).

• Evaluate RV size and function (2D). Estimate RV pressure if possible from the TR velocity (color Doppler, PW Doppler, and CW Doppler).
• Evaluate aortic root size and AV regurgitation (2D, color Doppler).

Anatomic Imaging

Acquisition

• Subcostal views

• Perform 2D sweeps to evaluate for obvious residual ASD or VSD. Use the short axis subcostal view to visualize the RVOT.

• Apical views

• Assess the size and function of both ventricles, in particular the RV.

• TOF repair often leads to long-standing severe PI, which can lead to right heart dilation and RV dysfunction.
• Previous ventriculotomy also contributes to RV dysfunction.
• As the right heart dilates, the angle of the TV annulus may tilt, the RV develops a “shoulder” near the free wall TV annulus, and the apex becomes broader (Fig. 7-9).
• Assessment of RV dilation remains a qualitative assessment.

• Visualize the VSD patch from the five-chamber (5C) view, assess for any obvious residual VSD.

• Parasternal views

• Optimize long axis 2D image for measurement of aortic annulus, root, sinotubular junction, and ascending aorta.
• The VSD patch can be visualized from long axis and short axis views; assess for any obvious residual VSD.
• Visualize the RVOT and branch PAs. Optimize view of branch PAs for measurement. If a conduit is present, pay attention to the motion of the conduit valve leaflets, which can become calcified and immobile over time.
• Assess the size and function of both ventricles.

• The RVOT in particular may demonstrate hypokinesis due to a history of ventriculotomy and the presence of a transannular patch.
• Compare the size of the RV with that of the LV in the short axis view (Fig. 7-10).
• Note whether RVH is present.

• Septal wall motion is often paradoxical after TOF repair. This finding is not concerning in and of itself. It may render shortening fraction an inaccurate assessment of LV systolic function.

• Suprasternal notch views: may be used to visualize branch PAs if not well seen from the parasternal short axis view.
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Figure 7-9 Apical view of a dilated right ventricle (RV) after repair of TOF. Note the broad right ventricular apex, the “shoulder” of the RV cavity near the lateral tricuspid annulus, and the tilt of the tricuspid valve (TV) annular plane relative to the plane of the MV.

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Figure 7-10 Parasternal short axis view of the RV and left ventricle (LV) after repair of TOF in a patient with severe RV dilation.

Analysis

• Measure the size of any residual ASD or VSD from the 2D views where best visualized.
• In the apical view, assess TV annulus angle. An angle greater than 20 degrees has been associated with RV volume greater than 150 mL/m2 (Fig. 7-11).
• Assess biplane LV ejection fraction in the apical view.
• Measure LV dimensions in the parasternal short axis or long axis view. Calculate shortening fraction if septal wall motion is not paradoxical.
• Measure branch PAs from the parasternal short axis view or the suprasternal notch view. Compare with norms for BSA (Z score) in smaller patients. Usual norms can be used for average adult-sized patients.
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Figure 7-11 Method for calculating TV annular tilt for assessment of RV dilation.

(From Punn R, Behzadian F, Tacy TA. Annular tilt as a screening test for right ventricular enlargement in patients with tetralogy of Fallot. J Am Soc Echocardiogr. 2010;23(12):1297–1302.)

Physiologic Data

• Doppler techniques are used to assess the following:

• Size, location, and direction of shunting of residual ASD and VSD.
• Atrioventricular valve (AVV) function.
• RVO and PAs for residual obstruction.
• Degree of PI.
• AV function.

Acquisition

• Subcostal views

• Perform color Doppler sweeps to identify any residual ASD or VSD. If present, assess direction of shunting. Assess velocity of shunting across any residual VSD.
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