Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

40. Tetralogy of Fallot with Pulmonary Regurgitation

Advances in diagnostic techniques such as echocardiography, cardiac surgery, and anesthesia, as well as improvement in postoperative management, have undoubtedly contributed to the excellent long-term outcome of patients with tetralogy of Fallot (TOF) following surgical repair. However, these patients present unique challenges because of potential residua and sequelae with increasing duration of follow-up. Right ventricular (RV) outflow tract (RVOT) reconstruction often includes infundibular muscle resection, pulmonary valvotomy or valvectomy, and RV outflow augmentation, and accounts for the most common long-term postoperative complications. Residual or recurrent RVOT obstruction and pulmonary regurgitation (PR) are important determinants of late morbidity, and the most common reason for reoperation. PR is primarily the result of the surgical ventriculotomy as well as extensive infundibulectomy and transannular patching of the RVOT at the time of surgical repair. This can often result in an RVOT aneurysm. Additional factors also contribute to the development and progression of PR, including (a) residual pulmonary valve (PV) abnormalities, (b) pulmonary annulus size, (c) peripheral pulmonary artery stenosis, (d) increased pulmonary vascular resistance, (e) RV diastolic dysfunction, (f) residual atrial and ventricular septal defects, and (g) acquired cardiovascular and pulmonary diseases, including pulmonary hypertension, sleep apnea, systemic hypertension, chronic lung disease, and kyphoscoliosis. Although chronic PR can be tolerated for many years, when left uncorrected, it often leads to progressive RV enlargement and dysfunction, progressive tricuspid valve regurgitation, and eventual right heart failure. PR is also associated with the late development of left ventricular (LV) dysfunction and is recognized as the most important risk factor for atrial and ventricular tachyarrhythmias, as well as sudden death. Assessment of patients with PR following repair of TOF often includes an electrocardiogram, chest radiograph, echocardiogram, exercise testing, cardiac magnetic resonance imaging (MRI), and cardiac catheterization in select patients. This chapter will focus on the echocardiographic assessment of PR following the repair of TOF.

The components of a comprehensive two-dimensional and Doppler transthoracic echocardiographic examination in patients with repaired TOF are summarized in Table 40.1. Each component is essential in the evaluation of patients with TOF to determine outcome and the need for reintervention. In preparation for the echocardiographic examination, it is essential to review the surgical records to obtain an accurate anatomic description of the repair. This ensures adequate understanding of the anatomic variability encountered in these patients and can be very useful as a guide for the echocardiographic examination.

ETIOLOGY AND SEVERITY OF PULMONARY REGURGITATION

PR following repair of TOF is commonly caused by resection of the PV at the time of surgical repair in combination with the concomitant ventriculotomy and transannular patching of the RVOT. These surgical interventions lead to enlargement of the PV annulus and progression to RVOT aneurysm and PR. Alternatively, pulmonary valvotomy, rather than valvectomy, is performed and may result in residual congenital PV abnormalities including stenosis and variable degrees of PR. Bicuspid PV is the most common congenital abnormality of the PV, with a reported incidence of up to 50%, followed by PV dysplasia or hypoplasia. TOF with absent PV occurs in 2% of patients and is associated with severe PR and massive enlargement of the pulmonary arteries. Optimal visualization of the RVOT is needed to assess the etiology and severity of PR. This is accomplished from the parasternal long- and short-axis views of the RVOT. At times, it is possible to image the RVOT from the apical four-chamber or subcostal windows with anterior angulation. These windows are very helpful in the adult patient with emphysema or in patients with poor parasternal windows (Fig. 40.1).

Pulmonary valve regurgitation is characterized by abnormalities in the spectral and color flow Doppler analysis of the RVOT. The severity of PR can be semiquantitatively assessed by echocardiographic techniques detailed in Table 40.2.

Color flow Doppler assessment of PR can be qualitative or quantitative. The two most common qualitative signs of severe PR are the presence of “free PR” and pulsation of the pulmonary arteries. It is not unusual in patients following TOF repair, and especially in those following PV valvectomy, to have “free” PR, whereby color flow Doppler demonstrates unobstructed bidirectional flow across the PV annulus. This severe regurgitation is often associated with vigorous pulsation of the main pulmonary artery and even the PA branches because of lower pulmonary artery diastolic pressure and a wider pulse pressure. The extent of the diastolic color flow signal caused by PR is often used as an indicator of its severity (Fig. 40.2). Brief flow reversal is normal in the branch pulmonary arteries in systole and early diastole because of the pulmonary artery geometry and differential branching of the right and left pulmonary arteries. This normal diastolic flow reversal is very limited in its duration and extent and is not associated with regurgitation into the right ventricle. On the other hand, the presence of persistent retrograde (>50% of the diastolic phase) PR flow in the branch pulmonary arteries that extends into the right ventricle is consistent with severe PR (Fig. 40.2B).

The RVOT area occupied by the regurgitant color flow Doppler signal can be used to assess PR severity. A PR area index, defined as the maximum area of the PR color jet on the parasternal short-axis imaging plane indexed to body surface area, has been shown to correlate well with the PR regurgitant fraction determined by angiography. Kobayashi demonstrated that the PR area index was 0.36 ± 0.29 in grade 1 angiographic PR, compared with 1.48 ± 0.46 in grade 2 and 2.80 ± 0.94 in grade 3 regurgitation. A significant positive linear correlation was observed between the two methods (r = 0.84, p <0.001). However, this technique is limited by two-dimensional image quality, the direction of the PR jet, machine gain settings, and transducer frequency. Given the potential limitations of area measurement, Williams et al. suggested using a linear measurement to assess the severity of PR. The PR jet/annulus ratio is defined as the ratio of the PR color Doppler jet width to the PV annulus dimension in early diastole on the parasternal short-axis view. This ratio has been demonstrated to correlate well with angiographic PR grade. In a study of 26 patients with PR following TOF repair, a PR jet/annulus ratio of 0.4 or less correlated with less than 1+ angiographic PR. On the other hand, a PR jet/annulus ratio of 0.7 separated patients with 2+ from those with 3+ angiographic PR. There was a significant positive correlation between angiographic PR grade and the color jet/annulus ratio (r = 0.95, p <0.001). In the same study, the presence or absence of diastolic flow reversal in the branch pulmonary arteries was assessed using pulsed-wave Doppler and/or color Doppler images in the parasternal short-axis view. Retrograde diastolic flow reversal was present in the branch pulmonary arteries in eight of nine patients with more than 2+ angiographic PR but in no patient who had less than 1+ angiographic PR. The positive and the negative predictive values of retrograde diastolic flow reversal in the branch pulmonary arteries for more than 2+ angiographic PR were 100% and 92%, respectively.

Figure 40.1. Subcostal view of the right ventricular outflow tract. Views without (A) and with (B) color flow Doppler demonstrate the absence of significant outflow tract obstruction (A) but severe pulmonary regurgitation. RV, right ventricle; PA, pulmonary artery.

Figure 40.2. Parasternal short-axis view demonstrating diastolic color flow Doppler in the right ventricular (RV) outflow tract. The red jet represents (A) mild and (B) severe pulmonary regurgitation. Notice the difference in the width and extent of the color flow jet that is limited to the RV outflow tract in A but extends from the branch pulmonary arteries in B. AV, aortic valve; LA, left atrium; PA, pulmonary artery; RV, right ventricle.

Other echocardiographic methods, including pulsed-wave and continuous-wave Doppler, have been used for the assessment of PR severity. Spectral Doppler assessment at the level of the PV in patients with PR demonstrates normal forward flow in systole and reversed flow in diastole (Fig. 40.3). In patients with less than severe PR, the diastolic flow reversal is holodiastolic (Fig. 40.3A) and its peak velocity is characteristically less than 1 m/s in the absence of pulmonary hypertension. The finding of a high-velocity regurgitant signal at end-diastole suggests a large difference between pulmonary artery diastolic pressure and RV end-diastolic pressure. On the other hand, in the presence of severe PR, there is early termination of the diastolic flow reversal signal by pulsed- or continuous-wave Doppler assessment (Fig. 40.3B). The regurgitant diastolic velocity peaks early and decreases rapidly as the pressure difference between the pulmonary artery and right ventricle rapidly equilibrates.

This finding is not pathognomonic for severe PR since it is also observed in patients with elevated RV end-diastolic pressure caused by RV diastolic dysfunction, which is not uncommon following TOF repair. However, in the presence of RV diastolic dysfunction, an additional presystolic Doppler forward flow (Fig. 40.4) is often noted. This is the result of end-diastolic RV pressure being higher than the pulmonary artery end-diastolic pressure, leading to forward flow across the PV annulus in late diastole after atrial contraction. This finding helps differentiate RV diastolic dysfunction from isolated severe PR.

Using the continuous-wave PR Doppler signal, further quantification of PR severity can performed by measuring the PV regurgitation index or pressure half-time. Li et al. suggested measuring the ratio of the duration of the continuous-wave PR Doppler signal to total diastolic time (PV regurgitation index) (Fig. 40.5A). This Doppler-derived index correlated closely with cardiac MRI–derived regurgitant fraction (r= –0.82, p <0.01) in a study of 53 consecutive patients with PR following TOF repair. Compared to cardiac MRI, a PR index of less than 0.77 had a 100% sensitivity and 85% specificity for identifying a PR fraction greater than 24%, with a predictive accuracy of 95%. This study also demonstrated that a PR jet width of greater than 0.98 cm had an accuracy of 90% in identifying the group with a PR fraction greater than 24% by MRI. These findings are in agreement with published reports suggesting that severe aortic regurgitation is associated with an LV outflow tract color jet width of greater than 1 cm. Using the same PR velocity profile by continuous-wave Doppler, the pressure half-time can be measured and used for the assessment of PR (Fig. 40.5B). PR pressure half-time was found to be inversely related to PR fraction in the absence of RVOT obstruction and RV diastolic dysfunction. In a prospective study of 34 adult patients with repaired TOF, Silversides et al. demonstrated that the mean pressure half-time measurements were 181 ± 75 ms in patients with a regurgitant fraction of less than 20% by cardiac MRI and 102 ± 29 ms with a regurgitant fraction greater than 40%. A pressure half-time of less than 100 ms demonstrated a high sensitivity and specificity for detecting significant PR.

Figure 40.3. Continuous-wave Doppler signal at the level of the pulmonary valve in a patient with mild pulmonary valve regurgitation. A: Normal systolic forward flow and reversed flow that continues throughout diastole, indicating mild pulmonary valve regurgitation. The low end-diastolic velocity suggests normal pulmonary artery diastolic pressure. B: In patients with severe pulmonary regurgitation, the regurgitant diastolic velocity peaks early and decreases rapidly as pulmonary artery and right ventricular pressures rapidly equilibrate leading to early termination of the continuous-wave Doppler signal, with return of the PR Doppler signal to the baseline.

Additional echocardiographic techniques for the assessment of PR severity include (a) measurement of regurgitant volume, fraction, and effective regurgitant orifice by two-dimensional and color Doppler techniques such as the proximal isovelocity surface area (PISA) and the continuity equation, and (b) measurement of the vena contracta. These techniques, however, are not as commonly used in the assessment of PR compared with the assessment of other valvular regurgitation. In addition, each of these techniques has significant limitations. The continuity equation, for example, requires quantitation of the difference between the total forward stroke volume calculated across the PV versus the normal cardiac output calculated across the aortic or tricuspid valve site. Measurement of the PV annular diameter, especially in postoperative patients, has inherent limitations and is subject to significant variability. The presence of tricuspid regurgitation and/or pulmonary stenosis can also affect the accuracy of these measurements. In addition, although PISA appears to be the most reliable method to assess regurgitant volume in patients with mitral and aortic regurgitation, PISA has not gained widespread use in patients with PR because the assumption of a hemispheric shape is not valid in most cases of PR in which flow rates and transorifice pressure gradients are especially low.

Figure 40.4. Assessment of right ventricular diastolic function in patients with pulmonary regurgitation following tetralogy of Fallot repair. Restrictive physiology leads to antegrade forward flow in the pulmonary artery during atrial contraction (double arrows). This should be noted during all phases of respiration and on five consecutive beats.

Figure 40.5. Continuous-wave Doppler signal across the right ventricular outflow tract demonstrating measurement of the pulmonary valve (PV) regurgitant index. Ratio of duration of the continuous-wave Doppler pulmonary regurgitation (PR) signal to total diastole (A) and pressure half-time for the assessment of PR severity (B).

RIGHT VENTRICULAR SIZE AND FUNCTION

The right ventricle in patients with TOF is inherently abnormal with significant hypertrophy and fibrosis that persists following surgical repair. Several additional preoperative and postoperative factors are known to contribute to the progressive RV enlargement and dysfunction, including significant tricuspid regurgitation, residual atrial or ventricular level shunts, and residual RVOT obstruction or pulmonary hypertension. RV size and function in repaired TOF are affected by the degree and duration of preoperative cyanosis and pressure overload, as well as factors related to the surgical repair itself, including RV injury secondary to a ventriculotomy, possible coronary artery injury, myocardial injury from inadequate myocardial preservation, and transannular patching within the RVOT. All of these factors are important determinants of the adaptive response of the right ventricle to volume overload from chronic PR. As the right ventricle dilates in response to PR, its ejection fraction initially increases because of the increased ventricular volume. With time, the RV ejection fraction decreases and is a reflection of a decrease in myocardial performance of the volume-loaded right ventricle. Progressive deterioration of myocardial function eventually results in decreased stroke volume with further increases in RV end-systolic and end-diastolic volume. In the current era, every effort is made to maintain PV competence at the time of surgical TOF repair in an attempt to prevent the potential long-term complications related to chronic PR. Current operative techniques often involve a combined transatrial and transpulmonary approach with a very limited RV incision, if needed, for patch augmentation of the RVOT and/or PV annulus. Under these circumstances, the use of a small stiff patch may provide a more superior hemodynamic result than a large expandable pericardial patch. This strategy may avoid significant PR at the expense of mild to moderate residual RVOT obstruction, which is usually well tolerated.

Assessment of RV size and function is a crucial component of the noninvasive evaluation of patients with repaired TOF. Unfortunately, most quantitative two-dimensional echocardiographic measurements of ventricular size and performance are based on the shape of the elliptical left ventricle; these geometric assumptions do not apply to the right ventricle. The right ventricle has a complex geometric shape with thinner walls and abundant coarse trabeculations that make endocardial border delineation challenging. The right ventricle appears to be crescent shaped in cross section and triangular in the lateral view. In addition, the RVOT is muscular and elongated, ending at the PV, which does not have a true bulbar annulus. These differences in ventricular morphology reflect the hemodynamically different roles of the two ventricles. Although the “eye-ball” technique has been commonly used to semiquantitatively assess RV size for many years, the 2010 ASE guidelines clearly state the importance of quantitative assessment of RV size. This however could be challenging in patients with congenital heart disease. Recently, a simple RV linear dimension obtained on transthoracic echo has been suggested as a valid quantitative assessment of RV size in repaired TOF. An RV internal dimension, obtained on parasternal short-axis imaging perpendicular to the mid intraventricular septum of >19.4 mm/m2 in end-systole or >24.5 mm/m2in end-diastole correlated well with cardiac MR-derived RV end-diastolic volume of >160 cc/m2. Three-dimensional echocardiography promises an accurate determination of RV volume and function. This technique continues to evolve, e.g., with smaller transducers and more improved software.

Given the limitations as a result of RV geometry, many nongeometric Doppler indices have been proposed that use systolic and diastolic time intervals and tissue Doppler imaging to provide indirect information about RV systolic and diastolic function in repaired TOF.

The Doppler assessment of the instantaneous rate of RV pressure increase (dP/dt) can be measured from the tricuspid regurgitant continuous Doppler velocity profile. dP/dt is measured by calculating the rate of RV pressure gradient increase—for example, from 4 mm Hg (1 m/s) to 16 mm Hg (2 m/s). However, this index is sensitive to changes in afterload and does not accurately reflect RV systolic function in patients with residual RVOT obstruction or pulmonary hypertension.

Tissue Doppler imaging quantitates myocardial velocities. For RV assessment, these velocities are measured at the level of the lateral tricuspid valve annulus near the insertion of the anterior tricuspid valve leaflet. These myocardial velocities are a marker of RV systolic and diastolic longitudinal motion. This relatively volume-independent echocardiographic velocity, obtained with or without color Doppler, has been demonstrated to be reduced in patients with repaired TOF compared with controls, and correlates well with reduced RV ejection fraction. Another Doppler-derived quantitative index of global ventricular function is the right-sided myocardial performance index (MPI). This index incorporates both systolic and diastolic parameters and is reported to be a measure of global ventricular function. The RV MPI is measured by dividing the sum of RV isovolumic contraction time and isovolumic relaxation time by the ejection time across the PV. Normal values for the RV MPI have been reported in both children (0.32 ± 0.03) and adults (0.28 ± 0.04). This index has been reported to be a valuable noninvasive method to assess RV function in patients with pulmonary hypertension, as well as Ebstein anomaly and, most recently, in repaired TOF. A study by Abd El Rahman et al. suggested that the MPI is affected by the severity of PR as well as the presence of RV diastolic dysfunction in repaired patients with TOF. All patients with PR had a lower than normal isovolumic relaxation time, while those with severe PR also had a prolongation of isovolumic contraction time compared with patients with mild to moderate PR (103 ± 57 versus 27 ± 41 ms, p <0.01). In addition, in the presence of a noncompliant right ventricle, the isovolumic relaxation time was shortened, paradoxically decreasing the RV MPI. Therefore, the sensitivity of the MPI in identifying RV dysfunction may be limited in repaired TOF. However, a recent study by Schwerzmann involving 57 adults with repaired TOF with significant PR demonstrated that a MPI of 0.40 or greater had an 81% sensitivity and an 85% specificity to identify patients with an RV ejection fraction of less than 35%. An MPI less than 0.25 had a 70% sensitivity and an 89% specificity to predict an RV ejection fraction of 50% or greater as determined by cardiac MRI. Yasuoka suggested the use of Doppler tissue imaging in the calculation of the MPI. Fifteen patients (6.3 ± 2.2 years old) with significant PR after TOF repair and 24 age-matched healthy children were analyzed. The MPI obtained by pulsed-wave Doppler was not different in patients with TOF repair compared with normal children (0.30 ± 0.12 versus 0.32 ± 0.07, p >0.05). However, when measured by tissue Doppler imaging, the MPI was significantly greater in patients with TOF than in normal children (0.48 ± 0.07 versus 0.30 ± 0.07, p <0.0001). Therefore, the authors suggest that the MPI measured by TDI is a more sensitive indicator of RV function in these patients and is a promising novel means of assessing global RV function in patients after TOF repair.

Another easily reproducible Doppler measurement of systolic RV contractile function that is less dependent on loading conditions has been used for assessment of RV function in repaired TOF. The isovolumic acceleration index (IVA) is calculated by dividing the myocardial velocity during isovolumic contraction by the time interval from its onset to the time at peak velocity. Frigiola reported that IVA is useful in detecting early preclinical RV dysfunction before the onset of clinical symptoms and may therefore be helpful in determining the optimal timing of PV replacement (PVR). Systolic RV function was evaluated by IVA, peak systolic myocardial velocity, and RV strain in 124 patients (age 21 ± 11 years) at a mean of 3.7 years after surgical repair. All of these parameters were noted to be reduced compared with normal controls. Patients with severe PR had a significantly lower IVA than those with mild or moderate PR (whereas systolic myocardial velocity and strain were not different between groups with varying severity of PR).

Tricuspid annular plane systolic excursion (TAPSE) and fractional area change (FAC) are newer echo-derived parameters of RV systolic function. A TAPSE of <13.5 mm was noted to be highly sensitive for detection of significant RV dysfunction as defined by cardiac MR-derived RV ejection fraction of <30%. A reduced FAC of the body of the RV, obtained from parasternal short-axis or four-chamber views, has been demonstrated to correlate well with reduced cardiac MR-derived RV ejection fraction.

As with patients with acquired heart disease and pulmonary hypertension, RV strain and strain rate indices have also been used for quantification of regional RV function in patients after repair of TOF. In repaired TOF, a progressive decrease in RV strain from the base to the apex has been demonstrated. Reduced RV global strain has also correlated well with reduced exercise capacity.

All of these parameters described above improve the quantitative echocardiographic assessment of RV function and could be considered as a surrogate for cardiac MR when the latter cannot be performed due to rhythm disturbance or endocardial pacemaker leads.

RV diastolic dysfunction is particularly common in repaired patients with TOF, especially after transannular patch placement, and has been associated with myocardial fibrosis on cardiac MR. In a study by Munkhammar et al., 47 patients with repaired TOF were evaluated by echocardiography. Restrictive RV physiology was commonly identified by the presence of late diastolic antegrade flow in the pulmonary artery, as shown in Figure 40.4. Ten percent of patients repaired before 6 months of age demonstrated restrictive physiology at the time of noninvasive follow-up. RV diastolic dysfunction was present in 38% of patients with repair after 9 months of age. Approximately one-third of patients with transannular patch repair demonstrated restrictive RV hemodynamics. The patients with restrictive RV hemodynamics had more severe preoperative pulmonary stenosis, were older at the time of TOF repair, and had a less severe degree of PR on serial echocardiographic follow-up.

RV diastolic dysfunction is believed to play a protective role with regard to the detrimental effect of severe PR in repaired TOF. RV diastolic dysfunction with elevation in RV diastolic pressure limits the duration of PR and subsequently the degree of RV dilatation. As a result, patients with severe PR and more restrictive RV physiology have smaller RV volume compared with those with severe PR and normal RV diastolic function. Therefore, assessment of RV diastolic function in patients with PR following TOF repair is an integral part of a comprehensive echocardiographic evaluation. However, brief antegrade late diastolic forward flow into the MPA may be present in normal subjects during inspiration and therefore should be noted in at least five consecutive beats.

The hepatic venous Doppler signal is also very helpful in the identification of RV diastolic dysfunction. Characteristic changes in this setting include higher diastolic forward velocity and a greater reversal of diastolic flow velocity with inspiration.

ADDITIONAL ECHOCARDIOGRAPHIC ASSESSMENT

The presence of residual infundibular, PV, and pulmonary artery branch stenosis, in association with PR, is not uncommon following repair of TOF. Peripheral pulmonary artery stenosis can result from pulmonary artery distortion by previous shunts, or from extension of the transannular patch to the branch PAs, or be secondary to poorly developed distal pulmonary arteries. Downstream obstruction because of branch pulmonary stenosis has been shown to worsen the severity of PR. One important role of echocardiography is to identify and characterize the site and severity of RVOT obstruction. Once the site of obstruction is identified, its severity can be assessed with pulsed-wave and continuous-wave Doppler. Pulsed-wave Doppler should be used to measure flow velocity proximal to the level of obstruction (V1), while the continuous-wave signal should be used to measure flow accelerating across the site of stenosis (V2). The peak Doppler gradient across the stenosis is then calculated using the simplified Bernoulli equation with the peak gradient being 4 (V2 – V1)2. In addition, the Doppler-derived tricuspid regurgitant velocity obtained by CW Doppler can be used to estimate RV systolic pressure using the same Bernoulli principle. The pulmonary artery pressure can then by calculated by subtracting the peak gradient across the PV from the RV systolic pressure. Therefore, echocardiography can be used for the estimation of both RV and pulmonary artery pressures. However, such measurements may be inaccurate because of suboptimal echocardiographic windows or the presence of multiple stenoses in series, long tunnel stenosis, or altered pulmonary artery geometry. Under these circumstances, cardiac catheterization with direct pressure measurement as well as angiography is recommended to best assess the location and severity of RVOT obstruction and for determination of pulmonary artery pressures. The presence of pulmonary hypertension in the setting of repaired TOF can be a residual from a previous systemic–to–pulmonary artery shunt (such as the Blalock-Taussig shunt), or may be related to a residual intracardiac shunt. At times, pulmonary hypertension may be related to acquired cardiovascular or chronic lung disease such as thromboembolism, kyphoscoliosis, emphysema, sleep apnea, systemic hypertension, or left heart failure. The presence of pulmonary hypertension worsens the severity of PR.

Tricuspid valve regurgitation is not uncommon following TOF repair but is rarely severe. Significant TR has been reported in up to 65% of patients following TOF repair. Tricuspid regurgitation can be caused by (a) an intrinsic tricuspid annular abnormality, (b) tricuspid valve dilatation caused by RV volume overload, (c) tricuspid valve damage during retraction during a transatrial surgical approach, and (d) damage to the tricuspid valve and its chordae during placement of the VSD patch. Significant tricuspid regurgitation can contribute to progressive RV enlargement and dysfunction; therefore, echocardiographic assessment of tricuspid regurgitation is an integral part of the noninvasive evaluation of these patients.

The presence of residual atrial or ventricular septal defects should be excluded by color flow Doppler with or without contrast echocardiography if needed. Residual ventricular septal defects can occur anywhere along the length of the VSD patch; however, these residual defects are most common in the area of the atrioventricular node where sutures are placed farther apart to avoid damage to the conduction system.

Although the left ventricle is not one of the primary anatomic cardiac defects seen in TOF, patients who have had previous TOF repair have been noted to have varying degrees of LV systolic and diastolic dysfunction as well as abnormalities of LV torsion. LV dysfunction plays an important role in the timing of PVR following TOF repair and is a powerful predictor of ventricular arrhythmias. Factors that are known to contribute to the development of LV dysfunction include (a) the duration of preoperative cyanosis, (b) the presence of LV volume overload from a previously placed systemic–to–pulmonary artery shunt, (c) suboptimal myocardial protection during cardiopulmonary bypass, (d) duration of cardiopulmonary bypass itself, (e) patching of the ventricular septum, (f) myocardial fibrosis, and (g) aortic valve regurgitation secondary to aortic root enlargement. Furthermore, Geva et al. suggested that LV dysfunction could be partly attributed to abnormal septal motion caused by the volume-overloaded right ventricle, as well as its detrimental effects on LV geometry and mechanical performance because of unfavorable ventricular–ventricular interaction. Cardiac MR and cardiac catheterization studies demonstrate a direct relationship between LV end-diastolic pressure and RV end-diastolic volume index. In the absence of abnormal septal motion, LV systolic function can be assessed by the well-standardized conventional M-mode methodology, two-dimensional echocardiographic techniques, and more recently 2D and 3D strain analysis. An important contributor to LV dysfunction in repaired TOF is the presence of aortic root dilatation with associated aortic regurgitation. Aortic root dilation is believed to be secondary to abnormal intrinsic properties of the aortic root as well as long-standing volume overload prior to TOF repair. Aortic regurgitation may develop secondary to aortic root dilatation or possibly as a result of direct damage during placement of the VSD patch.

Given the concerns about adaptability and the lack of reported symptoms in repaired TOF with severe PR, it is not uncommon for the clinician to rely on exercise stress testing to document significant changes in exercise capacity over time to aid in defining the optimal timing of PVR. Wessel et al. demonstrated that exercise performance was 82% ± 21% of predicted in repaired patients with TOF. Carvalho and coworkers showed significantly reduced duration of exercise in patients after TOF repair as well as a negative correlation between exercise time and the severity of PR. There is also substantial clinical interest in the diagnostic role of brain natriuretic peptide (BNP) in the assessment of patients with PR after TOF repair. Brili et al. reported that patients after repair of TOF had significantly higher BNP levels than in controls (85.0 ± 87 versus 5.4 ± 1.0 pg/mL, p <0.001) and that this increased BNP level correlated with RV enlargement. Ishii et al. examined the relationship between BNP and RV contractile reserve during exercise in 26 patients after TOF repair compared with 19 age-matched healthy children. Plasma levels of BNP were measured at baseline and at maximum exercise. Echocardiography combined with tissue Doppler imaging was performed at rest and during supine bicycle submaximal exercise. The peak value of RV dP/dT was also measured by continuous-wave Doppler. Plasma BNP levels were significantly higher in patients with TOF than in controls (44 ± 34 versus 6 ± 4 pg/mL, P value <0.01). In addition, a larger increment in BNP was noted after exercise in patients with TOF when compared with normal subjects (15 ± 12 versus 2 ± 2 pg/mL, p <0.01). At peak exercise, systolic myocardial tissue velocity and peak dP/dT values increased significantly in both groups. However, the magnitude of increase in both of these values was significantly less in patients with TOF than in controls (36% ± 19% versus 70% ± 19% and 42% ± 11% versus 81% ± 12%, respectively, with p <0.01). There was significant correlation between the increment in BNP and changes in systolic myocardial tissue velocity and dP/dt values. Furthermore, increments in BNP during exercise were well correlated with severity of PR. Therefore, exercise-induced changes in plasma concentration of BNP may reflect abnormalities in RV contractile reserve in patients with TOF. While it is too early to recommend that stress echocardiography be routinely performed, the future of such innovative techniques to assess anatomic and physiologic changes in repaired patients with TOF with PR appears promising.

COMPLEMENTARY INVESTIGATIVE TECHNIQUES IN PR

Cardiac MRI has emerged as a robust and reliable alternative technique for the quantitative assessment of RV volume, RV systolic function, and PR severity, especially when echocardiographic imaging is suboptimal. MRI offers an advantage over echocardiography in that image quality is not compromised by air, bone, or surgical scar. RV volume calculation by MRI correlates well with angiography. However, significant interobserver and intraobserver variability has been reported, primarily because of the complex geometry of the right ventricle. In addition, MRI techniques can underestimate the severity of PR compared with echocardiography. Although cardiac MRI is gaining momentum in the evaluation of patients with repaired TOF, its availability and familiarity compared with echocardiography are lacking. Furthermore, this technique may not provide all the necessary components of the comprehensive echocardiographic examination (see Table 40.1).

Impact of Echocardiographic Evaluation on Outcome

PVR remains the only treatment available for postoperative severe PR after TOF repair. PVR has proven long-term benefits, including reduction in RV size and improvement or stabilization of RV function. It has low operative risk when performed at an optimal time and in experienced medical centers. The optimal timing of PVR is determined by many factors, including the presence of clinical symptoms such as dyspnea, exercise intolerance, heart failure, and symptomatic or sustained arrhythmias. In addition, the presence of progressive RV enlargement and/or dysfunction, worsening tricuspid regurgitation, a significant residual shunt, or significant RVOT obstruction (right ventricular systolic pressure [RVSP] two-thirds systemic or greater) are indications for PVR with or without intracardiac repair. Furthermore, PVR is also considered when there is a documented decline in functional aerobic capacity on exercise stress testing. More recently, the right atrial–to–left atrial volume ratio has been noted to be another simple parameter that might be useful in timing for reintervention. Therefore, optimal patient selection for PVR is dependent on the information provided by the comprehensive serial echocardiographic examinations.

Recent advances in interventional cardiology have led to an increased interest in percutaneous PVR using a bovine jugular vein valve mounted on an expandable stent. An important determinant of patient suitability for this technique is the presence of favorable RVOT morphology. Three-dimensional echocardiography has been reported recently to provide additional anatomic details of RVOT anatomy that are incremental to that of two-dimensional echocardiography.

Following PVR, echocardiography is the most commonly used tool for serial assessment of the PV prosthesis, as well as RV size and function. Significant improvement in RV end-diastolic diameter but not in RV dysfunction is commonly observed with improvement in exercise tolerance. Pulmonary valve replacement also has a significant effect on LV function. However, considerable residua may persist such as ventricular dysfunction, aortic regurgitation, and pulmonary hypertension. These chronic conditions will need periodic serial echocardiographic assessment. In addition, echocardiography is an optimal technique for ongoing assessment of the PV prosthesis, whether biological or mechanical. These prostheses are almost always located directly retrosternal and are easily visualized by transthoracic echocardiography and at times are palpable on examination. Evaluation of leaflet motion, maximal and mean Doppler gradients, and identification of the presence and severity of prosthetic or periprosthetic regurgitation should be routinely performed.

SUMMARY

Assessment of patients following repair of TOF should include a thorough medical history, clinical examination, electrocardiogram, and comprehensive transthoracic echocardiogram to identify all postoperative residua and sequelae. PR is a common postoperative complication associated with progressive RV enlargement and dysfunction. These detrimental changes in RV performance are associated with progressive exercise intolerance, heart failure, tachyarrhythmias, and late sudden death. The echocardiogram plays a key role in identifying the optimal timing of PVR. Ongoing serial echocardiographic evaluation after valve replacement ensures appropriate follow-up in these patients.

SUGGESTED READING

Abd El Rahman MY, Abdul-Khaliq H, Vogel M, et al. Value of the new Doppler-derived myocardial performance index for the evaluation of right and left ventricular function following repair of tetralogy of Fallot. Pediatr Cardiol. 2002;23:502–507.

Aboulhosn JA, Lluri G, Gurvitz MZ, et al. Left and right ventricular diastolic function in adults with surgically repaired tetralogy of Fallot: a multi-institutional study. Can J Cardiol. 29(7): 866–872.

Alghamdi MH, Mertens L, Lee W, Yoo SJ, Grosse-Wortmann L. Longitudinal right ventricular function is a better predictor of right ventricular contribution to exercise performance than global or outflow tract ejection fraction in tetralogy of Fallot: a combined echocardiography and magnetic resonance study. Eur Heart J Cardiovasc Imaging. 14(3):235–239.

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Questions

1.The most common significant postoperative residua in Tetralogy of Fallot is which of the following?

A.Pulmonary regurgitation

B.Aortic insufficiency

C.Tricuspid regurgitation

D.Pulmonary stenosis

E.Coronary insufficiency

2.Which of the following echocardiographic findings is LEAST predictive of severe pulmonary regurgitation?

A.Holodiastolic color Doppler flow reversal in branch pulmonary arteries

B.Pulsations in main pulmonary artery

C.Increased pulmonary end diastolic velocity

D.Shortened pressure half-time

E.Large vena contracta

3.Diastolic forward flow across the pulmonary valve with atrial contraction is most consistent with:

A.RV systolic dysfunction

B.LV diastolic dysfunction

C.Branch pulmonary artery stenosis

D.Severe pulmonary regurgitation

E.RV diastolic dysfunction

4.Which of the following is the LEAST likely etiology of significant tricuspid regurgitation in the postoperative TOF patient?

A.Surgical damage to tricuspid valve during VSD patch placement

B.Intrinsic tricuspid annular abnormality

C.Tricuspid annular dilatation due to RV volume overload

D.Significant residual RV outflow obstruction

E.Small residual VSD

5.Which of the following is NOT a likely etiology for postoperative LV dysfunction in TOF patients?

A.Duration of preoperative cyanosis

B.Duration of cardiopulmonary bypass

C.Suboptimal myocardial protection during cardiopulmonary bypass

D.Severe pulmonary regurgitation

E.Myocardial fibrosis

6.Which of the following is TRUE concerning the myocardial performance index in postoperative TOF patients?

A.Normal value for RV MPI = 0.50 +/− 0.03

B.Decreased RV MPI value correlates with decreased RV EF%

C.Patients with severe pulmonary regurgitation have paradoxically decreased MPI

D.MPI is a measure of regional RV systolic function

E.Severe pulmonary regurgitation results in prolonged isovolumic relaxation time (IRT)

7.Which of the following is CORRECT regarding isovolumic acceleration (IVA)?

A.Calculated by dividing myocardial velocity during isovolumic contraction by time interval to peak velocity

B.Quantitative measure of RV diastolic function

C.Measured by continuous wave Doppler

D.Decreased values indicate better contractile function

E.More load dependent than mitral inflow Doppler

8.Which of the following is a quantitative measure of global RV function?

A.Tricuspid annular plane systolic excursion (TAPSE)

B.Myocardial performance index (MPI)

C.Isovolumic acceleration (IVA)

D.Fractional area change (FAC)

E.Tissue Doppler imaging

9.Pulmonary hypertension in the postoperative TOF patient is LEAST likely related to:

A.Previous Blalock-Taussig shunt

B.Residual VSD

C.Sleep apnea

D.Severe pulmonary regurgitation

E.Left heart failure

10.Which of the following would be LEAST contributory to an increasing severity of pulmonary regurgitation?

A.Branch pulmonary artery stenosis

B.Increased pulmonary vascular resistance (PVR)

C.Residual pulmonary valve abnormalities

D.Chronic lung disease

E.Tricuspid valve stenosis

Answers

1.Answer: A. Pulmonary regurgitation is the most significant postoperative residua in TOF patients. While aortic insufficiency and tricuspid regurgitation are also common, the severity of regurgitation is typically mild. Residual RVOT obstruction is also a common finding but is usually hemodynamically well tolerated in the majority of patients. Coronary insufficiency is usually not a major issue in TOF patients postoperatively.

2.Answer: C. The pulmonary end diastolic Doppler velocity returns to the baseline in patients with severe PR indicating equalization of RV and PA pressure. Holodiastolic color Doppler flow reversal in the branch pulmonary arteries, pulsations in the main pulmonary artery, a very abbreviated pressure halftime, and a large vena contracta are all hallmarks of severe PR.

3.Answer: E. This Doppler finding is classic for the stiff RV with decreased compliance. With atrial filling, diastolic pressure rises and results in antegrade flow across the pulmonary valve.

4.Answer: E. A residual VSD would likely result in LV volume overload if it is significant in size. The remainder of choices all result in a potentially significant degree of tricuspid regurgitation.

5.Answer: D. Postoperative LV dysfunction has been attributed to the duration of preoperative cyanosis prior to repair, the duration and adequacy of cardiopulmonary bypass techniques, and to the presence of myocardial fibrosis. Severe pulmonary regurgitation results in RV dilatation and dysfunction but likely has less of a hemodynamic impact on LV performance, except in those patients with severe degrees of dilatation and dysfunction.

6.Answer: C. Because severe pulmonary regurgitation results in shortening (or elimination) of isovolumic relaxation, the MPI is paradoxically decreased in TOF patients with severe PR. The MPI is a measure of global (systolic and diastolic) ventricular function with normal values of 0.32 +/− 0.03. Increased RV MPI values correlate with decreased RV EF at MRI.

7.Answer: A. IVA is a tissue Doppler measure of RV systolic contractility that is less load dependent than pulsed wave Doppler measures of mitral inflow. It is calculated by dividing myocardial velocity during isovolumic contraction by time interval to peak velocity. Increasing values indicate better contractility.

8.Answer: B. MPI is a global measure of combined systolic and diastolic function. TAPSE, IVA, and FAC are all systolic measures of function. Tissue Doppler can measure both systolic and diastolic myocardial velocities but is predominantly a regional parameter of function.

9.Answer: D. Pulmonary hypertension can be related to a previous BT shunt or a large residual VSD after repair of TOF. Left-heart failure with increased filling pressure as well as sleep apnea also can result in significant elevation of pulmonary pressures. Pulmonary hypertension exacerbates the degree of pulmonary regurgitation in this cohort.

10.Answer: E. The presence of tricuspid valve stenosis would be a very rare finding in the postoperative TOF patient and would not exacerbate the degree of pulmonary regurgitation. Distal branch obstruction, increased PVR, residual pulmonary valve abnormalities, and chronic lung disease are all reasonable candidates to increase the severity of PR in TOF patients.