Tetralogy of Fallot (TOF) is a morphologic diagnosis whose essential features include a large unrestrictive ventricular septal defect (VSD), right ventricular (RV) outflow tract (RVOT) obstruction, an overriding aorta, and RV hypertrophy (RVH) (Fig. 15.1). Although four seemingly disparate features are described, the syndrome actually results from a single morphologic abnormality—namely, anterior deviation or malalignment of the conal septum. All of the four cardinal features in TOF are a manifestation of this malalignment. This condition was first described by Stensen as early as 1672. However, it was Fallot in 1888 who provided the clinical-pathologic correlation of this malformation and termed it la maladie bleue.
The clinical features of TOF are very diverse and depend on the degree of RVOT obstruction. In this chapter, we will describe the echocardiographic morphology of this malformation in detail as well as the key features of the postoperative examination. We will also describe the morphologic aspects of TOF with absent pulmonary valve syndrome.
When describing the anatomic and echocardiographic morphology of TOF, a segmental approach should be used.
There is situs solitus in most cases of TOF. About 10% of patients may have a left superior vena cava (L-SVC) draining to the right atrium via the coronary sinus. This can be visualized in multiple echocardiographic scan planes. The parasternal long-axis view typically demonstrates a dilated coronary sinus—a finding that should prompt the echocardiographer to suspect a L-SVC. However, it should be noted that the coronary sinus is not always dilated in patients with a L-SVC, particularly in the following circumstances:
■Small L-SVC with prominent bridging innominate vein
■Elevated left atrial pressure, such as in patients with a predominant left-to-right shunt physiology (“pink tetralogy”)
■Termination of the L-SVC in the left atrium rather than the coronary sinus
In the parasternal short-axis view, a prominent venous structure is identified anterior to the left pulmonary artery. Slight clockwise rotation of the transducer will typically display the entire course of the left SVC in its long axis with drainage to the coronary sinus along the posterior aspect of the heart. Color flow mapping and pulsed-wave Doppler confirm that this blood vessel is venous and demonstrates low-velocity phasic systolic and diastolic flow toward the heart. Other vascular structures in this area that may be confused with a L-SVC include the following:
■Ascending vertical vein (anomalous pulmonary venous connection) in which venous flow is away from the heart
■The left upper pulmonary vein as it crosses the left pulmonary artery may be confused with a L-SVC, particularly when a long length of this vein can be visualized (as in infants). However, this vein can be tracked distally to the hilum of the left lung to define its origin.
■Levo-atrial cardinal vein: this venous structure is a connection from the left atrium to a systemic vein and thus has flow away from the heart. Almost all cases of levo-atrial cardinal vein are associated with left-sided obstructive lesions, particularly left atrial outlet obstruction. This vein generally courses posterior to the left pulmonary artery (unlike the anterior course of the L-SVC).
Approximately one-third of patients with unrepaired TOF have an ASD. Many additional patients have a small patent foramen ovale. Defects in the atrial septum are best imaged from the subcostal scan planes because the atrial septum is perpendicular to this imaging plane. The atrial septum can be visualized in orthogonal subcostal planes (coronal and sagittal) to optimally define the ASD. A subcostal sagittal (short-axis) view provides excellent visualization of the inferior vena cava (IVC) and SVC connections and the ASD. Patients without significant RVH and without severe RVOT obstruction will have a predominant left-to-right shunt at the atrial level. Conversely, those with significant RVH or RVOT obstruction will have a bidirectional or predominantly right-to-left atrial level shunt.
Figure 15.1. Anatomical components of tetralogy of Fallot. Anterior malalignment ventricular septal defect, pulmonary stenosis, overriding aorta, and right ventricular hypertrophy.
It is important to remember that for color flow mapping of right-to-left atrial level shunt the Nyquist limit must be reduced to as low as 30 to 50 cm/s to optimally demonstrate the shunt. A predominant right-to-left shunt at the atrial level is generally considered an indication for surgical intervention in patients with TOF.
Most cases of tetralogy of Fallot have concordant atrioventricular connections. The tricuspid and mitral valves are usually structurally normal. Significant atrioventricular valve pathology is uncommon. However, in approximately 2% of patients with TOF, a complete atrioventricular septal defect may be present—particularly in patients with Down syndrome. In such cases, the apical four-chamber view demonstrates a typical image of a large primum atrial defect and a large inlet VSD. Many of these common AV valves are Rastelli Type C (i.e., free floating—without chordal attachments of the anterior bridging leaflet to the interventricular septum).
VENTRICULAR SEPTAL DEFECT
The typical VSD in patients with TOF is an anterior malalignment type of outlet VSD. The conal/infundibular septum is deviated anteriorly from the muscular septum (Fig. 15.2). This single malformation results in RVOT obstruction (by encroaching on the RVOT), RVH (secondary to RVOT obstruction), and aortic override (due to the malaligned conal septum) (Fig. 15.3). In other words, the four components of TOF are in reality the result of a single malformation—anterior malalignment of the conal septum.
Figure 15.2. Pathologic specimen of tetralogy of Fallot. Anterior deviation of the conal septum (CS) into the right ventricular outflow tract (RVOT) results in a large malalignment ventricular septal defect (asterisk) with aortic override (Ao) as well as significant RVOT obstruction and RV hypertrophy. RA, right atrium; RV, right ventricle. (Photograph courtesy of Dr. William Edwards.)
This anteriorly malaligned VSD occurs in the vast majority of patients with TOF; however, other anatomic types of VSD may occur. A description of the anatomical and echocardiographic assessment of the different types of VSD in patients with TOF is listed next:
Figure 15.3. Pathologic specimen of tetralogy of Fallot. Anatomic four-chamber view demonstrating large ventricular septal defect with aortic override. (Photograph courtesy of Dr. William Edwards.)
Figure 15.4. Parasternal long-axis view in tetralogy of Fallot. Note the large ventricular septal defect (VSD; asterisk) with approximately 50% aortic override (Ao) of the VSD.
■Anteriorly malaligned VSD (74%): This represents a large subaortic defect that extends from the right and noncoronary cusps of the aortic valve superiorly to the membranous septum inferiorly. The defect is well seen in the parasternal long-axis view (Fig. 15.4). The anterior malalignment of the conal septum with an overriding aorta is obvious from this view. However, this image is not pathognomonic of TOF because this malaligned VSD with an overriding aorta may be seen in patients with pulmonary atresia with VSD and in those with truncus arteriosus. Hence, it is critical to define the morphology of the pulmonary valve and RVOT.
By rotating the transducer clockwise, a parasternal short-axis view at the base of the heart is obtained. The extent of the VSD is well seen in this view extending from the area of aortic-tricuspid continuity (membranous septum) often up to the crista supraventricularis (“12 o’clock” position in the parasternal short-axis view) (Fig. 15.5). A prominent “knuckle” of the anteriorly malaligned conal septum is often evident in this view leading to the os infundibulum where the RVOT obstruction typically begins (Fig. 15.6A–B). The demonstration of a pulmonary valve in this view with antegrade flow across it excludes the possibilities of pulmonary atresia with VSD and truncus arteriosus.
Figure 15.5. Parasternal short-axis view in tetralogy of Fallot. Note the large ventricular septal defect (asterisk) with anterior deviation of the conal septum (CS) into the right ventricular outflow tract (RVOT). Ao, aorta.
The direction of the VSD shunt flow should be visualized by color flow Doppler as well as by pulsed-wave and continuous-wave Doppler. Patients with mild to moderate degrees of RVOT obstruction will have predominant left-to-right shunting, while more severe degrees of RVOT obstruction often lead to bidirectional and, later, predominantly right-to-left shunting.
■Perimembranous VSD without aortic-tricuspid fibrous continuity due to a muscular rim (18%)
■Atrioventricular septal defect in continuity with the subaortic defect (2%)
■Inlet VSD with straddling tricuspid valve (1%)
■Doubly committed subarterial defect (5%): In this setting, there is a complete lack of conal septum. In the parasternal short-axis view, the VSD is noted to extend beyond the crista supraventricularis (“12 o’clock position”) up to the pulmonary valve. This VSD is usually separated from the tricuspid valve by a muscular rim. RVOT obstruction is most commonly due to pulmonary valve stenosis and concomitant annular hypoplasia and not due to infundibular stenosis.
Figure 15.6. Parasternal short-axis view in tetralogy of Fallot. A: Note the prominent deviation of the conal septum (CS) into the right ventricular outflow tract (RVOT), resulting in significant narrowing. B: Color Doppler. Note that obstruction, represented by a mosaic pattern in the color flow Doppler signal, begins within the RVOT and extends into the pulmonary artery. *Ventricular septal defect. AoV, aortic valve.
In general, all of these types of VSD in TOF are unrestrictive. Restrictive VSDs are rare in the setting of TOF but can occur (approximately 1%). The reason for restriction is generally the presence of accessory tricuspid tissue within the VSD. Rarely, a hypertrophied septal band may also contribute to a restrictive VSD.
Spectral Doppler analysis and color flow mapping of the VSD provide a wealth of physiologic information. In patients with mild RVOT obstruction, the predominant interventricular shunting will be left-to-right. Such patients have a physiology consistent with a large VSD and are at risk of developing congestive heart failure and pulmonary hypertension. These patients are generally referred to as having “pink tetralogy.” With increasing degrees of RVOT obstruction, the VSD shunt may be bidirectional (Fig. 15.7A–B). Eventually, with severe RVOT obstruction, the ventricular level shunt is predominantly right-to-left. These patients are cyanotic and may be at risk of developing hypercyanotic spells (“tet spells”). Flow across the VSD is almost always laminar when the VSD is unrestrictive.
The ventriculoarterial connections in TOF are typically concordant. However, the aorta does characteristically override the ventricular septum. This override is best demonstrated in the parasternal long-axis view (see Fig. 15.4) but is also obvious in other views, including the apical four-chamber view (Fig. 15.8). It must be pointed out that even in normal individuals, there can be some degree of aortic override. A spectrum exists in the setting of this anomaly from less than 50% override in patients with TOF to greater than 50% aortic override (predominant RV origin of the aorta) in patients with double-outlet right ventricle. It is also important to understand that the position of the transducer on the chest wall can affect the visual impression of aortic override.
The Right Ventricular Outflow Tract
Assessment of the RVOT is critically important in patients with TOF. Anterior and cephalad deviation of the conal septum leads to characteristic narrowing of the RVOT. This muscular obstruction often begins at the crista supraventricularis and extends to the pulmonary valve annulus. The RVOT can be visualized in multiple echocardiographic views. The subcostal 4-chamber (coronal) and short-axis (sagittal) views are useful to delineate the morphology of the RVOT and define obstructive muscle bundles (Fig. 15.9A–D). The parasternal short-axis view helps to differentiate TOF from other congenital heart lesions, including truncus arteriosus and pulmonary atresia with VSD, all of which may have a similar echocardiographic appearance in the parasternal long-axis view (see Fig. 15.4). In TOF, the parasternal short-axis view demonstrates a patent RVOT and pulmonary valve (see Figs. 15.5 and 15.6A–B).
Figure 15.7. Parasternal long-axis view in tetralogy of Fallot. Color Doppler demonstrates left-to-right shunting (red flow) in systole (A) and right-to-left shunting (blue flow) in diastole (B).
Figure 15.8. Apical view in tetralogy of Fallot. Note the aortic override (Ao) of the ventricular septal defect (asterisk). RV, right ventricle; LV, left ventricle.
The pulmonary annulus is often hypoplastic and the pulmonary valve may be acommissural, unicommissural, bicommissural, or tricommissural with thickening/dysplasia (Fig. 15.10). Accurate measurement of the pulmonary annulus is important and may determine the necessity for transannular patch repair if significant hypoplasia exists. The z-score of the pulmonary valve annulus should be recorded. In general, a pulmonary annular z-score of less than –2 is likely to indicate the need for a transannular surgical approach. In the extreme form, the pulmonary valve may be completely atretic. However, because the clinical and surgical management and anatomical variations of this anomaly are very different from TOF, the entity of pulmonary atresia with VSD is considered separately. The presence and severity of pulmonary valve regurgitation should also be noted (Fig. 15.11A–C).
Figure 15.9. Subcostal four-chamber (coronal) and short-axis (sagittal) views in tetralogy of Fallot. A: Note the prominent deviation of the conal septum (CS) into the right ventricular outflow tract (RVOT) in this subcostal four-chamber view. B: Aliasing of color flow Doppler in this subcostal four-chamber view demonstrates obstruction within the RVOT. C: Subcostal short-axis view demonstrating deviation of CS into RVOT. D: Subcostal short-axis view with color Doppler aliasing within the RVOT demonstrating region of obstruction within RVOT.
Figure 15.10. Pathologic specimens of the pulmonary valve in tetralogy of Fallot. Anatomical variability of the pulmonary valve in tetralogy of Fallot, including acommissural, unicommissural, bicommissural, and dysplastic tricommissural valves. (Photograph courtesy of Dr William Edwards)
Figure 15.11. Severe pulmonary regurgitation in postoperative tetralogy of Fallot. A: Color Doppler demonstrating broad jet of pulmonary regurgitation extending into the branch pulmonary arteries consistent with severe (“free”) regurgitation. B: Continuous-wave Doppler demonstrating return of the pulmonary regurgitant signal to the Doppler baseline consistent with equalization of right ventricular (RV) and pulmonary arterial pressure. Systolic Doppler velocity of 1.6 m/s confirms a widely patent RV outflow tract (RVOT) without significant residual obstruction.
Often there is supravalvar stenosis noted in the main pulmonary artery. Typically, this is located at the tips of the open pulmonary valve in systole and the valve may have attachments in this region. Recognition of this narrowing is important because patch angioplasty of the main pulmonary artery may be needed to relieve this obstruction during surgical repair. This abnormality is well visualized in the high left parasagittal view. The anatomy of the branch pulmonary arteries is important to define. These pulmonary artery branches are best visualized in the parasternal short-axis view as well as the high left parasternal and suprasternal short-axis views (Fig. 15.12). In fact, measurements of the right pulmonary artery from the suprasternal short-axis view correlate better with angiography-derived measurements than those from parasternal views. Branch pulmonary artery z-scores should be calculated and focal stenoses should be identified. Severe branch pulmonary artery hypoplasia may make complete repair difficult. Staged palliation with a primary systemic-pulmonary artery shunt may be necessary.
It is also important to document additional sources of pulmonary arterial blood supply. Pulmonary blood flow may be provided entirely by antegrade flow across the pulmonary valve, via the ductus arteriosus (occasionally bilateral ductal arteries) or via multiple aortopulmonary collateral vessels. With a left aortic arch, the ductus arteriosus generally arises from the upper descending aorta, whereas with a right aortic arch, the ductus remains left-sided but arises from the base of the (left) innominate artery. The ductus arteriosus is best visualized in the high left parasagittal view and suprasternal long-axis view (Fig. 15.13). Color flow mapping and Doppler evaluation are invaluable in accurately determining the ductal physiology. A continuous left-to-right ductal shunt is suggestive of severe RVOT obstruction, particularly if significant antegrade flow is not demonstrated. Continuous multiple tortuous channels of systemic-to-pulmonary artery flow are typical of aortopulmonary collaterals and are far more common in pulmonary atresia with VSD rather than in TOF.
Assessment of the degree of RVOT obstruction requires a comprehensive echocardiographic approach including two-dimensional evaluation of anatomic features, color flow mapping, and spectral Doppler analysis. Aliasing may be noted in the subvalvar region with color flow mapping (Fig. 15.14A–B). Pulsed-wave Doppler is helpful to delineate the area of maximal obstruction, while continuous-wave Doppler should be used to determine the maximal instantaneous and mean systolic gradients (Fig. 15.15A–C). Although the maximal instantaneous RVOT gradient is often reported, the mean gradient often correlates better with the peak-to-peak gradient measured at cardiac catheterization. To avoid underestimation of the RVOT gradient, it is important to remember to use lower-frequency probes and particularly the non-imaging probe for high-quality Doppler analysis. It should also be noted that in the presence of a large patent ductus arteriosus, the RVOT gradient may be underestimated. Similarly, the gradient is sometimes low in the neonatal period despite significant obstruction due to elevated “downstream” pulmonary arteriolar resistance.
Figure 15.12. Branch pulmonary arteries in tetralogy of Fallot (TOF). A: Parasternal short-axis scan demonstrating right ventricular outflow tract (RVOT), main pulmonary artery (MPA), and branch pulmonary arteries after TOF repair. B: Laminar color flow Doppler across the RVOT into the pulmonary arteries.
Figure 15.13. Suprasternal long-axis scan demonstrating origin of a patent ductus arteriosus (PDA) from the proximal descending aorta in tetralogy of Fallot. The aortic arch was left-sided in this patient. Ao, aorta.
Finally, the side of the aortic arch must be defined. Up to 25% to 30% of patients with TOF have a right-sided aortic arch, usually with mirror image branching. A right aortic arch is more common with increasing degrees of RVOT obstruction. The suprasternal short-axis sweep will optimally define this anomaly. In patients with a right aortic arch, the first brachiocephalic branch travels to the left and bifurcates into the left common carotid and left subclavian arteries (if there is mirror image branching). In addition, the tracheal air column can often be identified and the arch can be noted to extend to the right of the tracheal air column.
Figure 15.14. Modified subcostal four-chamber view in tetralogy of Fallot. A: Anterior deviation of the conal septum (CS) into the right ventricular outflow tract (RVOT). B: Color Doppler demonstrates aliased flow in the RVOT. RV, right ventricle; RA, right atrium.
Up to 10% of patients with TOF have coronary artery anomalies that may potentially affect surgical management. The unifying feature of important coronary artery anomalies is the presence of a coronary artery crossing the RVOT (Fig. 15.16A–B). A prominent conal branch is frequently seen arising from the right coronary artery that supplies the infundibulum. More importantly, the anterior descending coronary artery may arise from the right coronary artery. There may be paired anterior descending coronary arteries: one from the right coronary artery and one from the left coronary artery. A prominent conal branch can be differentiated from an anterior descending artery in that a conal branch terminates in the infundibulum, while an anterior descending coronary artery will occupy the interventricular groove.
TETRALOGY OF FALLOT WITH ABSENT PULMONARY VALVE SYNDROME
A small subset of patients with TOF have an “absent pulmonary valve” in which the pulmonary valve annulus is represented by dysplastic tissue. This dysplastic tissue is often obstructive but is always regurgitant. Severe pulmonary regurgitation is present, even in the fetus, leading to RV dilation. The pulmonary arteries are characteristically aneurysmally dilated, and this severe dilation often negatively affects pulmonary development. The ductus arteriosus is frequently absent. It has been hypothesized that during gestation, in the absence of the normal pulmonary valve, aortic outflow returns back through the ductus arteriosus to the right ventricle and then returns to the left ventricle through the VSD, thus creating the pathophysiology of severe aortic regurgitation. This “circular shunt” may be incompatible with fetal life. Clinically, postnatal respiratory symptoms are often more severe than cardiac symptoms. The echocardiographic examination demonstrates intracardiac anatomy very similar to TOF with pulmonary stenosis; however, the pulmonary annulus is represented by dysplastic remnants of tissue and the main and branch pulmonary arteries are massively dilated. The surgical repair of this condition involves restoration of pulmonary valve competency using a valved conduit, often a pulmonary homograft. The pulmonary arteries characteristically need reduction arterioplasty.
Figure 15.15. Evaluation of right ventricular outflow tract (RVOT) obstruction in tetralogy of Fallot. A: Continuous-wave Doppler interrogation across the RVOT and pulmonary artery from a parasternal short-axis orientation. Note both the peak gradient and mean gradient are assessed. B: Pulsed-wave Doppler in the RVOT proximal to the pulmonary valve demonstrates a late peaking Doppler profile consistent with mild dynamic RVOT obstruction. C: Continuous-wave Doppler demonstrating both Doppler profiles (dynamic and fixed RVOT obstruction) within the same signal.
Figure 15.16. Tetralogy of Fallot. A: Normal coronary arterial patterns in tetralogy of Fallot. B: Major coronary artery anomalies in tetralogy of Fallot. (Adapted with permission from Jureidini SB, Appleton RS, Nouri S. Detection of coronary artery abnormalities in tetralogy of Fallot by two-dimensional echocardiography. J Am Coll Cardiol. 1989;14:960–967.)
PULMONARY ATRESIA WITH VENTRICULAR SEPTAL DEFECT
Pulmonary atresia and ventricular septal defect (PA-VSD) is considered the most severe form of tetralogy of Fallot. However, the complexity and variability of the pulmonary outflow tract anatomy and branch pulmonary artery architecture in PA-VSD sets this lesion apart from tetralogy of Fallot and defining this anatomy is integral to appropriate surgical decision making.
Echocardiography is useful in the diagnosis of patients with PA-VSD and in differentiating these patients from those with TOF or truncus arteriosus. Due to the complex patterns of the pulmonary artery blood supply in patients with PA-VSD, cardiac catheterization or ancillary multimodality imaging with cardiac MR or CT is often required. In general, patients with PA-VSD have similar intracardiac anatomy to those with tetralogy of Fallot by 2D imaging. Parasternal long-axis imaging shows an overriding aorta with an anterior malaligned ventricular septal defect. In the parasternal short-axis view, patients with PA-VSD typically have a well-formed muscular wall between the right ventricle and main pulmonary artery resulting in atresia with no outlet to the pulmonary artery. Parasternal short-axis imaging can also help define the presence or absence of a central pulmonary artery confluence and assess the degree of hypoplasia of the main pulmonary artery and branch pulmonary arteries.
Defining the pulmonary artery blood supply is a key factor in surgical management and is done by both echocardiography and cardiac catheterization. The identification of aortopulmonary collaterals by echocardiography can be difficult due to their multiple locations and vascular course. Aortopulmonary collaterals arise most commonly from the descending aorta, followed by subclavian arteries, and lastly the abdominal aorta. The pulmonary artery blood supply can be divided into three major patterns, with the first type consisting of confluent branch pulmonary arteries supplied by the ductus arterious. In this type, cardiac catheterization is usually not required if there is an absence of collateral vessels. Cardiac catheterization is required when there are multiple aortopulmonary artery collaterals with or without a central PA confluence.
Echocardiography can also define other anatomic anomalies associated with PA-VSD such as the anterior malaligned VSD, additional VSDs, atrial septal defects, and coronary anomalies. Aortic arch sidedness and branching pattern should also be identified since there is a high incidence of a right aortic arch as in TOF.
SURGICAL MANAGEMENT OF TETRALOGY OF FALLOT
TOF was one of the first congenital heart lesions to undergo surgical correction. However, high mortality was reported in this early surgical era that was related to many factors, including difficulties with cardiopulmonary bypass techniques. This led to the widespread adoption of a two-stage repair strategy including an initial palliative systemic-to-pulmonary artery shunt performed early in infancy and a subsequent complete repair performed later in infancy or childhood. Introduction of systemic-to-pulmonary artery shunts, such as the Blalock-Taussig shunt in 1945, was devised as a method of providing palliation to severely affected patients. Subsequently, the Potts (1946) and Waterston (1962) shunts were introduced. Both of these palliations were subsequently found to have a high incidence of pulmonary arterial hypertension and pulmonary arterial distortion. Subsequently, the classic Blalock-Taussig shunt was gradually replaced by the modified Blalock-Taussig shunt using a GORE-TEX interposition graft. This graft was naturally restrictive, thus providing controlled pulmonary blood flow and a lower risk of pulmonary artery distortion.
The surgical approach for complete repair of TOF continues to evolve. The initial intracardiac repair for TOF was performed by Lillehei and colleagues in 1954 using controlled cross-circulation, while the first successful repair using a heart-lung machine was made by Kirklin and colleagues in 1955. With improving surgical results, the age at complete repair has been gradually decreasing and presently surgery is routinely done in early infancy. The emphasis in this early surgical area had been complete relief of RVOT obstruction, even at the cost of creating free pulmonary regurgitation. It is now well recognized that severe pulmonary regurgitation is not well tolerated in the long term. Late postoperative sequelae of cardiac arrhythmias, RV dysfunction, tricuspid valve insufficiency, and sudden cardiac death tend to be more frequent with greater severity of pulmonary regurgitation and RV dilation. Thus, the surgical emphasis has changed from complete relief of RVOT obstruction to preservation of a competent pulmonary valve, if possible, even at the expense of mild residual RVOT obstruction.
While this may represent an oversimplification of a complex surgical decision making process, the major surgical repair goals remain the same: closure of the VSD, relief of RVOT obstruction, and, if possible, preservation of pulmonary valve competency. A patent foramen ovale or small ASD may, at times, be intentionally left to act as a “pop-off” valve for the right ventricle, particularly if there is significant RV hypertrophy. This may facilitate the postoperative management by augmenting systemic cardiac output at the expense of mild arterial desaturation. If there is a patent ductus arteriosus, it is generally ligated.
SURGICAL REPAIR OF TETRALOGY OF FALLOT
1. Systemic-pulmonary artery shunt: A modified Blalock-Taussig shunt may be performed either through a left thoracotomy or via a midline sternotomy. Currently, this staging palliation is less commonly performed due to excellent surgical outcomes following complete repair of TOF in infancy. However, if the neonate is premature or of low birth weight with significant cyanosis or hypercyanotic spells, a palliative Blalock-Taussig shunt may be considered. Contraindications to cardiopulmonary bypass may also lead to consideration of a palliative systemic-pulmonary shunt. The presence of coronary artery anomalies that require an RV–pulmonary artery conduit placement may also be an indication for a primary shunt procedure to allow an eventual larger right ventricle–to–pulmonary artery conduit.
2. Right ventricular outflow tract patch: In patients who have an adequate sized pulmonary annulus, VSD closure is performed followed by resection of muscle from within the RVOT. Augmentation with an RVOT patch that does not include incision across the pulmonary annulus (to preserve pulmonary valve competency) may also be performed. A concomitant pulmonary valvotomy may be performed to relieve valvar stenosis. This is generally the method of choice when pulmonary valve annular z-score is greater than –2 SD.
3. Transannular RVOT patch: In patients with significant pulmonary annular hypoplasia, a transannular extension of the RVOT patch repair may be needed. This involves incising the pulmonary valve annulus in addition to the RVOT with placement of an onlaid patch. This often effectively relieves RVOT obstruction but leaves the patient with severe regurgitation, likely necessitating future pulmonary valve replacement. This approach is generally used in patients with a pulmonary valve annular z-score of –2 SD or less. More recently, some surgeons have advocated the placement of a monocusp valve (using a very thin patch of GORE-TEX) within the outer transannular patch to function as a temporary “valve” due to its redundancy. Although these monocusp valves tend to degenerate in the early postoperative period, the absence of free pulmonary regurgitation following surgical repair is thought to aid the immediate postoperative course.
4. Right ventricle–to–pulmonary artery conduit repair: In simple anatomical variants of TOF, a RV–pulmonary artery conduit repair is uncommon, except in the presence of an anomalous coronary artery that crosses the infundibulum and precludes an incision in the RVOT. Rarely, complex multilevel obstruction may exist including chordal attachments or complex subvalvar stenosis that may be best managed by RV–pulmonary artery conduit placement.
POSTOPERATIVE ECHOCARDIOGRAPHIC EXAMINATION
With continually improving surgical outcomes after TOF repair, there is an ever-increasing number of patients who present for postoperative evaluation. The key areas of interest in the postoperative period include evaluation for residual intracardiac shunts (Fig. 15.17A–D) (atrial or ventricular), the presence of a pericardial effusion (early postoperative examination), detailed anatomical assessment of the RVOT, and serial quantitative evaluation of ventricular size and function.
Residual VSDs are often identified at the margins of the VSD patch and, unless they are large, are not well seen with two-dimensional imaging alone. Color flow Doppler typically demonstrates a left-to-right shunt (because the RVOT obstruction is largely relieved). Continuous-wave Doppler interrogation of the late systolic VSD jet provides an estimation of the left ventricle–to–right ventricle pressure gradient. The early systolic gradient is generally unreliable due to delayed activation of the right ventricle with concomitant postoperative right bundle branch block. These small VSD patch defects often resolve over a period of several months due to endothelialization of the VSD patch. It is also important to recognize the presence of additional muscular defects that may be identified for the first time after surgical VSD closure. These small muscular defects are often missed before surgical repair due to equal ventricular pressures. Parasternal long- and short-axis views as well as the apical five-chamber view are optimal for identifying these residual defects and for Doppler interrogation. Coronary artery fistulas may also be seen after RVOT muscle resection and are characterized by continuous or predominantly diastolic Doppler flow signals into the right ventricle. The atrial septum should be interrogated to determine if an atrial level shunt persists. The direction of atrial shunting should also be assessed.
Assessment of the Right Ventricular Outflow Tract
There may be persistent RVOT obstruction after surgical repair of TOF. It is important to optimally define the location(s) of this obstruction at the subvalvar, valvar, or supravalvar level(s). Assessment of the peak and mean outflow gradient should be assessed by continuous-wave Doppler interrogation. If there is sufficient tricuspid regurgitation, the estimated RV systolic pressure serves as a validation to corroborate the measured RVOT gradient (Fig. 15.18A–B). In case of discrepancy, it is important to remember that the derived RV pressure estimate by tricuspid regurgitation is usually more accurate.
Figure 15.17. Postoperative tetralogy of Fallot (TOF). A: Apical five-chamber view demonstrating ventricular septal defect (VSD) patch (asterisk) repair in TOF. B: Color Doppler interrogation reveals an intact VSD patch without residual intracardiac shunting. C: Parasternal long-axis scan in same patient demonstrating the VSD patch repair (arrow). D: Color Doppler interrogation again reveals no evidence of residual shunting around the VSD patch. Ao, aorta; RV, right ventricle; LV, left ventricle.
Assessment of the branch pulmonary arteries is important since there can be distal stenoses. Although the visualization of branch pulmonary artery anatomy may be problematic in the older postoperative patient, a combination of parasternal short-axis, high left and right parasternal, and suprasternal views may allow adequate noninvasive assessment of this anatomy. With increasing frequency, centers have begun to use computed tomography (CT) or magnetic resonance imaging (MRI) to delineate more accurately the presence and severity of distal pulmonary arterial branch obstruction in patients with limited postoperative echocardiographic windows.
The assessment of pulmonary regurgitation is a critical part of the serial noninvasive evaluation of the postoperative TOF patient (see Fig. 15.11A–B). The key echocardiographic features of severe pulmonary regurgitation include the following:
Figure 15.18. Tricuspid regurgitation in postoperative tetralogy of Fallot (TOF). A: Parasternal short-axis scan demonstrating eccentric tricuspid regurgitation (TR) (arrow) along the site of ventricular septal defect (VSD) repair (asterisk). TR should not be confused with a residual intracardiac shunt. B:Continuous-wave Doppler interrogation of TR predicting normal right ventricular pressure post TOF repair (22 mm Hg + right atrial pressure). AoV, aortic valve; RVOT, right ventricular outflow tract.
■Laminar, low-velocity regurgitant flow by color Doppler
■Diastolic flow reversal in the branch pulmonary arteries (Fig. 15.11A)
■The pulsed-wave Doppler signal of pulmonary regurgitation demonstrates a rapid return to baseline (Fig. 15.11B). Physiologically, this implies that the pulmonary artery pressure is equal to RV pressure early in diastole.
It is important to exclude “downstream” obstruction, such as pulmonary artery branch stenosis, that can exacerbate the severity of pulmonary regurgitation. With severe pulmonary regurgitation, there is often an increased systolic outflow Doppler velocity across the RVOT and pulmonary valve in the absence of obstruction secondary to the increased RV stroke volume. Typically, this Doppler velocity does not exceed 2.5 m/s.
Assessment of Right Ventricular Systolic Function
The anatomical and hemodynamic consequences of severe pulmonary valve regurgitation over a prolonged period of time include RV dilation (Fig. 15.19A–C), hypertrophy, and dysfunction. Accurate assessment of RV size and function remains important, particularly because indications for pulmonary valve replacement following TOF repair include the development of RV dysfunction or progressive RV dilation. However, unlike with the left ventricle, there are many inherent limitations in the ability to assess the right ventricle by two-dimensional echocardiography. These limitations include the following:
■The shape of the right ventricle is complex and precludes geometric assumptions that are used in calculating LV systolic function.
■Due to the proximity of the right ventricle to the anterior chest wall, there is an inherent limitation in image resolution due to near-field effects. This limited resolution particularly affects evaluation of the anterior wall of the right ventricle.
■The three parts of the right ventricle, namely, the inlet, the body, and the outlet (infundibulum), are typically not imaged together in any one echocardiographic plane. Thus, two-dimensional assessment has to include multiple echocardiographic planes, which are often limited following surgical repair and in older individuals.
Due to these issues, there have been a multitude of parameters that have been suggested to quantify systolic function of the right ventricle. Some of these methodologies are presented next.
Fractional Area Change
Fractional area change (FAC) is measured by planimetry of the area of the right ventricle, typically in the apical four-chamber view. FAC has been shown to correlate with MRI-derived ejection fraction. Limitations of this methodology include the need to visualize the entire endocardial border, which may be difficult in some patients, and the lack of inclusion of the RV infundibular region in the functional assessment. Also, FAC in the parasternal short-axis view has not been adequately validated and likely has low reproducibility because the exact level at which FAC is determined may differ between studies and between examiners. Using FAC also assumes uniformity of function throughout the right ventricle, which may not be the case. In addition, it is not uncommon to see discrepant results between FAC in the apical four-chamber view and the parasternal short-axis view, because the two represent contraction in different echocardiographic planes. Normal FAC in the apical four-chamber view ranges from 32% to 60%.
Figure 15.19. Right ventricular (RV) dilatation after tetralogy of Fallot repair. A: Apical four-chamber view demonstrating significant RV enlargement. B: Parasternal short-axis scan demonstrating RV dilatation. C: M-mode demonstrating paradoxical septal wall motion secondary to RV volume overload. RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle.
Tricuspid Annular Systolic Plane Excursion
Because the fibers of the right ventricle are predominantly longitudinal in orientation (unlike the left ventricle, which has primarily circumferential fibers), systolic shortening in the RV occurs primarily in the ventricular long axis. Tricuspid annular systolic plane excursion (TASPE) has been used as an index of RV function. In adults, normal TASPE determined by M-mode echocardiography is >2.0 cm. TASPE has recently been reported in pediatric patients and correlates with both age and body surface area.
Myocardial Performance Index
The myocardial performance index (MPI), also termed the Tei index, is a Doppler-derived measure of combined systolic and diastolic ventricular function. This index can often be measured even if the anatomical two-dimensional images of the right ventricle are suboptimal. The MPI is calculated as follows:
where ICT is isovolumic contraction time, IRT is isovolumic relaxation time, and ET is ejection time.
In practice, ICT + IRT + ET is equal to atrioventricular (AV) valve closure-to-opening time, which is easily measured from the pulsed-wave Doppler inflow signal (tricuspid inflow for the right ventricle, mitral inflow for the left ventricle). The ejection time is measured from the pulsed-wave Doppler signal across the semilunar valve (pulmonary valve for the right ventricle, aortic valve for the left ventricle). The equation can be simplified to:
In general, an MPI greater than 0.35 ± 0.05 is abnormal for either ventricle.
Tissue Doppler Imaging
Tissue Doppler echocardiography involves the measurement of myocardial velocities during different phases of the cardiac cycle. Signals from the blood pool are filtered out and only signals from myocardial motion are analyzed. Three distinct waves are generally recognized: the systolic (s’) wave, the early diastolic wave (e’), and the late diastolic (a’) wave. Higher velocities generally correlate with better ventricular function. Normative values have been established for pediatric and adult populations. In addition, the isovolumic acceleration (IVA) can also be calculated by dividing the peak isovolumic velocity by the time to peak velocity. IVA has been proposed as a relatively load-independent index of ventricular function and can be applied to both left ventricular and RV functional assessment.
Strain and Strain Rate Imaging
Strain and strain rate imaging are relatively new tools that measure myocardial deformation. Strain is the change in the length of an object (e.g., the myocardium) with respect to its original length, while the rate of change is termed strain rate. These indices are used as a measure of regional myocardial function. Strain can be derived by both Doppler technology and tissue tracking technology, which has the advantage of being angle independent (unlike Doppler-derived strain). Commercially available software is now readily available to analyze strain and strain rate. Relatively small studies have established normal values of strain and strain rate in children and adolescents. Abnormalities of strain and strain rate have been demonstrated in patients after repair of TOF.
The use of three-dimensional echocardiography in the assessment of RV volume and function is now well established. Studies have shown good correlation between three-dimensional echo–derived ejection fraction and cardiac MRI. Software for the analysis of RV volumes is now commercially available.
In clinical practice, echocardiographers use a variety of methodologies to determine RV size and function. More recently, cardiac MRI and CT have been shown to provide accurate quantitative assessment of RV volume and function. These evaluations are most commonly performed before planned surgical intervention to corroborate the findings of echocardiography. MRI and CT do not have inherent limitations such as poor echocardiographic windows and do not depend on geometric assumptions to calculate ventricular volumes and function.
Assessment of Right Ventricular Diastolic Function
The quantitative assessment of RV diastolic function in patients with TOF also is challenging from an echocardiographic perspective. Evidence of restrictive RV filling can be demonstrated by pulsed-wave Doppler interrogation within the RVOT and proximal main pulmonary artery (Fig. 15.20). The presence of antegrade flow into the main pulmonary artery with atrial contraction is the Doppler hallmark of a “stiff” noncompliant RV. Tissue Doppler echocardiography has also been shown to demonstrate abnormalities of RV diastolic function in patients after TOF repair.
Figure 15.20. Restrictive right ventricular (RV) filling in postoperative tetralogy of Fallot. Parasternal short-axis scan with pulsed-wave Doppler interrogation in the main pulmonary artery. Note the antegrade forward flow (asterisks) into the pulmonary artery with atrial contraction. This Doppler pattern is consistent with decreased RV compliance.
TOF is one of the most common cyanotic congenital heart defects. Accurate anatomical and physiologic delineation is mandatory before surgical repair, and with high-quality echocardiographic evaluation, the need for angiography and cardiac catheterization can be largely avoided. Careful postoperative surveillance after repair of TOF is critical. Timing of late postoperative pulmonary valve replacement remains a matter of controversy and is discussed later in this text.
Anderson RH, Weinberg PM. The clinical anatomy of tetralogy of Fallot. Cardiol Young. 2005;15(Suppl 1):38–47.
Berry JM Jr, Einzig S, Krabill KA, et al. Evaluation of coronary artery anatomy in patients with tetralogy of Fallot by two-dimensional echocardiography. Circulation. 1988;78:149–156.
Blalock A, Taussig HB. The surgical treatment of malformations of the heart in which there is pulmonary stenosis or pulmonary atresia. JAMA. 1945;128:189–202.
Dabizzi RP, Caprioli G, Aiazzi L, et al. Distribution and anomalies of coronary arteries in tetralogy of Fallot. Circulation. 1980;61:95–102.
D’Hooge J, Heimdal A, Jamal F, et al. Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations [erratum appears in Eur J Echocardiogr. 2000;1:295–299. Eur J Echocardiogr. 2000;1:154–170.
Eidem BW, McMahon CJ, Cohen RR, et al. Impact of cardiac growth on Doppler tissue imaging velocities: a study in healthy children. J Am Soc Echocardiogr. 2004;17:212–221.
Ettedgui JA, Sharland GK, Chita SK, et al. Absent pulmonary valve syndrome with ventricular septal defect: role of the arterial duct. Am J Cardiol. 1990;66:233–234.
Fellows KE, Freed MD, Keane JF, et al. Results of routine preoperative coronary angiography in tetralogy of Fallot. Circulation. 1975;51:561–566.
Gatzoulis MA, Balaji S, Webber SA, et al. Risk factors for arrhythmia and sudden cardiac death late after repair of tetralogy of Fallot: a multicentre study. Lancet. 2000;356:975–981.
Gladman G, McCrindle BW, Williams WG, et al. The modified Blalock-Taussig shunt: clinical impact and morbidity in Fallot’s tetralogy in the current era. J. Thorac Cardiovasc Surg. 1997;114:25–30.
Harada K, Toyono M, Yamamoto F. Assessment of right ventricular function during exercise with quantitative Doppler tissue imaging in children late after repair of tetralogy of Fallot. J Am Soc Echocardiogr. 2004;17:863–869.
Hui W, Abd El Rahman MY, Dsebissowa F, et al. Comparison of modified short-axis view and apical four chamber view in evaluating right ventricular function after repair of tetralogy of Fallot. Int J Cardiol. 2005;105: 256–261.
Jonas RA. Tetralogy of Fallot with pulmonary stenosis. In: Jonas RA, ed. Comprehensive Surgical Management of Congenital Heart Disease. London: Arnold, 2004:279–300.
Kirklin JW, Blackstone EH, Pacifico AD, et al. Routine primary repair vs two-stage repair of tetralogy of Fallot. Circulation. 1979;60:373–386.
Kirklin JW, DuShane JW, Patrick RT, et al. Intracardiac surgery with the aid of a mechanical pump-oxygenator system (Gibbon type): report of eight cases. Proc Mayo Clin. 1955;30:201.
Lang RM, Bierig M, Devereux RB, et al. Recommendations for chamber quantification: a report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr. 2005;18:1440–1463.
Lillehei CW, Cohen M, Warden HE, et al. Direct vision intracardiac surgical correction of the tetralogy of Fallot, pentalogy of Fallot, and pulmonary atresia defects; report of first ten cases. Ann Surg. 1955;142:418–442.
Morris DC, Felner JM, Schlant RC, et al. Echocardiographic diagnosis of tetralogy of Fallot. Am J Cardiol. 1975;36:908–913.
Murphy JG, Gersh BJ, Mair DD, et al. Long-term outcome in patients undergoing surgical repair of tetralogy of Fallot. N Engl J Med. 1993;329:593–599.
Papavassiliou DP, Parks WJ, Hopkins KL, et al. Three-dimensional echocardiographic measurement of right ventricular volume in children with congenital heart disease validated by magnetic resonance imaging. J Am Soc Echocardiogr. 1998;11:770–777.
Pigula FA, Khalil PN, Mayer JE, et al. Repair of tetralogy of Fallot in neonates and young infants. Circulation. 1999;100(19 Suppl):II157–II161.
Potts WJ, Smith S, Gibson S. Anastomosis of the ascending aorta to a pulmonary artery. JAMA. 1946;132:627–631.
Reddy VM, Liddicoat JR, McElhinney DB, et al. Routine primary repair of tetralogy of Fallot in neonates and infants less than three months of age. Ann Thorac Surg. 1995;60(6 Suppl):S592–S596.
Schwerzmann M, Samman AM, Salehian O, et al. Comparison of echocardiographic and cardiac magnetic resonance imaging for assessing right ventricular function in adults with repaired tetralogy of Fallot. Am J Cardiol. 2007;99:1593–1597.
Silvilairat S, Cabalka AK, Cetta F, et al. Echocardiographic assessment of isolated pulmonary valve stenosis: which outpatient Doppler gradient has the most clinical validity? J Am Soc Echocardiogr. 2005;18:1137–1142.
Silvilairat S, Cabalka AK, Cetta F, et al. Outpatient echocardiographic assessment of complex pulmonary outflow stenosis: Doppler mean gradient is superior to the maximum instantaneous gradient. J Am Soc Echocardiogr. 2005;18:1143–1148.
Siwik ES, Patel CR, Zahka KG. Epidemiology and genetics [by Goldmuntz E]. In: Allen HD, Gutgesell HP, Clark EB, et al., eds. Heart Disease in Infants, Children and Adolescents. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2001:880–902.
Snider RA, Serwer GA, Ritter SB. Echocardiography in Pediatric Heart Disease. 2nd ed. St. Louis: Mosby, 1997.
Therrien J, Provost Y, Merchant N, et al. Optimal timing for pulmonary valve replacement in adults after tetralogy of Fallot repair. Am J Cardiol. 2005;95:779–782.
Uretzky G, Puga FJ, Danielson GK, et al. Complete atrioventricular canal associated with tetralogy of Fallot. Morphologic and surgical considerations. J Thorac Cardiovasc Surg. 1984;87:756–766.
van Straten A, Vliegen HW, Lamb HJ, et al. Time course of diastolic and systolic function improvement after pulmonary valve replacement in adult patients with tetralogy of Fallot. J Am Coll Cardiol. 2005;46:1559–1564.
Vick GW 3rd, Serwer GA. Echocardiographic evaluation of the postoperative tetralogy of Fallot patient. Circulation. 1978;58:842–849.
Vogel M, Cheung MM, Li J, et al. Noninvasive assessment of left ventricular force-frequency relationships using tissue Doppler-derived isovolumic acceleration: validation in an animal model. Circulation. 2003;107:1647–1652.
Waterston DJ, Stark J, Ashcraft KW. Ascending aorta-to-right pulmonary artery shunts: experience with 100 patients. Surgery. 1972;72:897–904.
Weidemann F, Eyskens B, Jamal F, et al. Quantification of regional left and right ventricular radial and longitudinal function in healthy children using ultrasound-based strain rate and strain imaging. J Am Soc Echocardiogr. 2002;15:20–28.
Weidemann F, Eyskens B, Mertens L, et al. Quantification of regional right and left ventricular function by ultrasonic strain rate and strain indexes after surgical repair of tetralogy of Fallot. Am J Cardiol. 2002;90:133–138.
Zilberman MV, Khoury PR, Kimball RT. Two-dimensional echocardiographic valve measurements in healthy children: gender-specific differences. Pediatr Cardiol. 2005;26:356–360.
1.Which of the following is the MOST common coronary artery anomaly in patients with Tetralogy of Fallot?
A.Anomalous left circumflex coronary artery from the right coronary artery
B.Anomalous left anterior descending coronary artery from the right coronary artery
C.Single left coronary artery
D.Anomalous left coronary artery from pulmonary artery
E.Anomalous left coronary artery from right sinus of Valsalva
2.Which of the following is the MOST common associated cardiac anomaly in patients with Tetralogy of Fallot?
A.Cleft mitral valve
B.Sinus venosus atrial septal defect
C.Right aortic arch
D.Persistent left superior vena cava to coronary sinus
E.Retroaortic innominate vein
3.What is the MOST common type of VSD in patients with TOF?
4.What is the BEST echocardiographic view to demonstrate the degree of aortic override of the ventricular septum?
5.What is the MOST common hemodynamically significant post-operative surgical finding in patients with Tetralogy of Fallot?
D.Residual RVOT obstruction
6.Which of the following BEST assesses longitudinal RV function in post-operative patients with Tetralogy of Fallot?
A.Fractional area change (FAC)
D.RV myocardial performance index (MPI)
E.Tricuspid anular plane systolic excursion (TAPSE)
7.Which of the following is NOT consistent with severe post-operative pulmonary valve regurgitation?
A.Laminar low-velocity color Doppler regurgitant flow
B.Broad color Doppler regurgitant jet
C.Diastolic reversal of color Doppler flow in the branch pulmonary arteries
D.Prolonged regurgitant pressure halftime
E.PR continuous wave Doppler signal with rapid return to baseline
8.Which of the following is TRUE regarding patients with Tetralogy of Fallot with absent pulmonary valve?
A.Hypoplastic branch pulmonary arteries
B.Absent pulmonary valve leaflets
C.Significant respiratory distress is common
D.Large non-restrictive patent ductus arteriosus is always present
E.Stenosis is uncommon due to lack of valve leaflets
9.Which of the following is LEAST consistent with long-standing severe pulmonary regurgitation in the post-operative patient with Tetralogy of Fallot?
A.Severe right ventricular dilatation
B.Moderate tricuspid regurgitation
C.Paradoxical septal wall motion
D.Dilated main and branch pulmonary arteries
E.Restrictive RV diastolic filling
10.Which of the following is CORRECT regarding the patent ductus arteriosus in patients with tetralogy of Fallot?
A.Typically arises from base of innominate artery in patients with left aortic arch
B.Additional multiple aorto-pulmonary artery collaterals common
C.Most commonly are bilateral in TOF patients
D.Continuous left-to-right shunting suggests severe RVOT obstruction
E.Best visualized in subcostal imaging planes
1.Answer: B. The most common coronary artery anomaly in TOF is an anomalous LAD from the RCA. Dual LADs or a prominent conal branch from the RCA are also common variants in TOF.
2.Answer: C. A right aortic arch is present in approximately 25% of patients with TOF. Persistent left SVC to coronary sinus can be found in up to 10% of TOF patients. The presence of a cleft mitral valve, sinus venosus ASD, or retroaortic innominate vein is uncommon in these patients.
3.Answer: A. The anatomic hallmark of TOF is an anterior malalignment VSD that results in RVOT obstruction and aortic override of the VSD.
4.Answer: E. While present in other views, the best view to define the degree of aortic override in TOF patients is the parasternal long-axis view.
5.Answer: C. Longstanding significant pulmonary regurgitation is the most significant surgical sequela in TOF resulting in significant right ventricular dilatation and dysfunction. While often present, residual VSD or RVOT obstruction, aortic insufficiency, or tricuspid regurgitation are often clinically more mild and better tolerated hemodynamically in these patients.
6.Answer: E. TAPSE assesses the longitudinal motion and velocity of the tricuspid annulus in the longitudinal direction. The remainder of the listed methods assess the global performance of the right ventricle.
7.Answer: D. The pressure halftime in severe PR is very short and returns quickly to the Doppler baseline. The remainder of these choices are all hallmarks of severe PR in TOF patients.
8.Answer: C. Patients with TOF with an “absent” pulmonary valve have remnants of pulmonary valve tissue with resultant severe regurgitation and variable degrees of stenosis. This anatomic abnormality results in severe dilatation of the branch pulmonary arteries in utero and significant postnatal respiratory distress due to these dilated vessels compressing the airways. A patent ductus arteriosus is often absent in this lesion.
9.Answer: E. RV volume overload due to longstanding pulmonary regurgitation results in RV dilatation, paradoxical septal motion, and dilatation of the pulmonary arteries. Dilatation of the RV can also result in tricuspid annular dilatation with resultant tricuspid regurgitation. Restrictive right-ventricular filling often limits the degree of pulmonary regurgitation in TOF patients resulting in less RV dilatation and other hemodynamic changes.
10.Answer: D. The PDA in patients with TOF is typically left-sided and best visualized in the high-left parasternal imaging window. The PDA typically arises from the proximal descending aorta when the arch is left-sided and from the base of the innominant artery when the arch is right-sided. Additional aorto-pulmonary collaterals are much more common in pulmonary atresia with VSD than in patients with TOF. Continuous left-to-right shunting does suggest significant RVOT obstruction.