|Year : 2021 | Volume
| Issue : 1 | Page : 24-30
Echocardiographic Evaluation of Postoperative Patient with Tetralogy of Fallot: A Step-Wise Approach
Sakshi Sachdeva, Sivasubramanian Ramakrishnan
Department of Cardiology, All India Institute of Medical Sciences, New Delhi, India
|Date of Submission||26-Jul-2020|
|Date of Acceptance||30-Aug-2020|
|Date of Web Publication||05-Apr-2021|
Dr. Sivasubramanian Ramakrishnan
Room Number 10, 8th Floor, Department of Cardiology, Cardio Thoracic Science Center, All India Institute of Medical Sciences, Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
As tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease, with the advancements in cardiac surgical techniques, there has been an ever-increasing number of postoperated patients with this condition. TOF repair is denoted as “total correction,” however, many hemodynamic and electrophysiologic sequelae remain or come into picture over time, which need to be tackled for the improvement of quality of life and life expectancy. Therefore, regular life-long follow-up is required after TOF surgery. During follow-up visits, only clinical assessment does not suffice, and various investigations are employed from time to time. These include electrocardiogram, echocardiogram, computed tomogram angiography, perfusion scanning, cardiac catheterization, and cardiac magnetic resonance imaging. Echocardiography nevertheless, is the easiest, quickest, noninvasive and overall, the most informative investigation. In this review, step-by-step echocardiographic evaluation of a postoperated TOF patient is described.
Keywords: Adult congenital heart disease, echocardiogram, postoperated, tetralogy of Fallot
|How to cite this article:|
Sachdeva S, Ramakrishnan S. Echocardiographic Evaluation of Postoperative Patient with Tetralogy of Fallot: A Step-Wise Approach. J Indian Acad Echocardiogr Cardiovasc Imaging 2021;5:24-30
|How to cite this URL:|
Sachdeva S, Ramakrishnan S. Echocardiographic Evaluation of Postoperative Patient with Tetralogy of Fallot: A Step-Wise Approach. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2021 [cited 2021 Jul 23];5:24-30. Available from: https://www.jiaecho.org/text.asp?2021/5/1/24/313088
| Introduction|| |
Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease beyond neonatal age. Surgical repair of TOF is the most common pediatric cardiac surgical intervention performed among children presenting with cyanosis. Surgery for TOF had started as early as 1955, and there have been progressive improvements in surgical techniques over the years, thus improving the long-term outcomes and longevity of postoperative patients. The surgical intervention commonly called “total correction,” is far from correction, rather it is the best palliation as it relieves the patient of cyanosis and cyanotic spells, but later predisposes to postoperative medical and surgical complications in due course of time on follow-up., Many investigations, mainly electrocardiogram (ECG), echocardiogram and sometimes computed tomogram (CT) and magnetic resonance imaging (MRI) are routinely included in the follow-up evaluation of postoperative TOF patients. In this review, stepwise approach to echocardiographic evaluation of postoperative TOF patients is discussed.
Surgical repair of TOF entails ventricular septal defect (VSD) closure and right ventricular (RV) infundibular muscle resection in all the patients. Transannular patch (TAP) across pulmonary valve and pulmonary artery (PA) plasty of main PA (MPA) or branch pulmonary arteries are needed in a proportion of patients. There is a need of RV to PA conduit placement if there is a coronary artery crossing the RV outflow tract (RVOT) thus limiting the use of TAP. Before any imaging evaluation, one must go through the operative notes (if available) to best understand the anatomy, and hemodynamics. Special care must be taken about the timing of echocardiography along with elaborate assessment of structural and functional details. Yearly ECG and echocardiogram are recommended in asymptomatic patients. Beyond 10 years of age, echocardiogram is recommended every 2 yearly unless significant hemodynamic abnormality is present. Step-wise analysis of all the cardiac segments is done. The guidelines provide an exhaustive framework, but the follow-up care has to be individualized in each patient taking cues from the guidelines.
[Table 1] shows various structural and functional abnormalities in postoperated TOF patients. In its native state, the right ventricle in TOF is under pressure overload. However, after surgical repair, when the pulmonary stenosis is relieved, the functioning of pulmonary valve is disrupted and pulmonary regurgitation (PR) sets in. Since the PA pressure in TOF is normal, this volume overload due to low-pressure PR is tolerated well intially. However, as the time progresses, this volume overload causes progressive dilatation of the RV which eventually becomes dysfunctional. Therefore, one of the major goals of echocardiography in repaired TOF is to identify this progressive dilatation of the RV before significant ventricular dysfunction develops. [Table 2] enlists the goals of echocardiographic assessment in postoperated TOF.
|Table 1: Various functional and the causative structural abnormalities in postoperated tetralogy of Fallot patients|
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|Table 2: Goals of echocardiographic assessment in postoperated tetralogy of Fallot|
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| Study of Right Ventricle|| |
The RV faces the maximum physiologic burden in TOF. Therefore, the study of RV is of utmost importance. The RV is hypertrophied in TOF as it faces systemic pressures. Hence, there is diastolic dysfunction and restrictive physiology. During surgery, RV undergoes ventriculotomy and infundibular muscle resection to relieve the outflow obstruction. This might lead to systolic dysfunction of RV. During RVOT obstruction (RVOTO) relief, the function of pulmonary valve gets compromised and there is PR, which leads to progressive RV volume overload and dysfunction. Hence, after surgery both systolic and diastolic function of the RV, and also the features of RV volume overload should be assessed.
Right ventricular size and assessment for right ventricular volume overload
Right ventricle is located retrosternally and has highly variable geometrical conformation. These factors make its imaging as a single unit difficult because it does not conform to a standard geometrical model unlike the left ventricle (LV). Three-dimensional (3D) echocardiography has not fully evolved for routine estimation of RV volumes and hence, MRI studies are preferred as gold standard when precise RV volume needs to be assessed. As MRI cannot be done very frequently due to the logistic and financial concerns, echocardiography is used for volume assessment and if convincing evidence of enlargement or dysfunction is present, MRI is advised to get accurate values. On transthoracic echocardiogram, RV is assessed from multiple acoustic windows using two-dimensional (2D) echocardiography.
Right ventricular focused apical four-chamber view
This view is made by modifying the usual apical four-chamber view, such that, both the crux and the apex of RV are visible, to avoid foreshortening [Figure 1]. RV dimensions are measured in this view. RV end-diastolic cross-sectional area <20 cm2/m2 body surface area has been associated with MRI-measured RV end-diastolic volume index <170 mL/m2. A diameter >42 mm at the base and >35 mm at the mid-ventricular level indicate RV dilatation. These latter cutoff values are not adjusted to body size.
|Figure 1: Right ventricular focused apical four-chamber view on echocardiogram, so as to include the right ventricle apex and free wall in the imaging sector. Right ventricular basal and mid-cavity dimensions are measured at end-diastole|
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Parasternal short axis view
Normal RV is crescentic shaped as seen from this view. Compared to LV, if the RV short-axis anteroposterior diameter is greater, at the level of the papillary muscles, it is considered severely enlarged. Interventricular septum (IVS) position gives a fair idea of the pressure/volume overload of RV. Flattening or leftward displacement of the IVS, results in a D-shaped LV [Figure 2]. Systolic flattening of the ventricular septum suggests RV pressure overload, whereas diastolic septal flattening indicates RV volume overload. In short axis view at the level of aortic valve, RVOT diameter is measured. Proximal RVOT diameter >35 mm and distal RVOT diameter >27 mm indicate RV dilatation [Figure 3].
|Figure 2: Parasternal short axis view showing dilated right ventricle. Interventricular septal position is deviated towards left ventricular at end diastole, indicating volume overload of the right ventricle. Left ventricle is D-shap|
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|Figure 3: Echocardiogram in short axis view at the level of aortic valve showing measurement right ventricular outflow tract diameter. Proximal right ventricular outflow tract diameter is the linear dimension measured from the anterior right ventricular wall to the aortic valve. Distal right ventricular outflow tract diameter is the linear transversal dimension measured just proximal to the pulmonary valve at end-diastole|
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Systolic right ventricular function
In general, eye-balling method is used to assess RV function, but this qualitative assessment is inferior to the quantitative method. Quantitative assessment gives a baseline, which can be used to compare any deterioration/improvement later. The parameters used to assess RV systolic function include RV fractional area change (RVFAC), tricuspid annular plane systolic excursion (TAPSE), and tissue Doppler assessment.
Right ventricular fractional area change
The percentage RV FAC is a measure of RV systolic function. It is calculated by the formula ([end-diastolic area-end-systolic area]/end-diastolic area) × 100. The RV endocardial border is traced in end-systole (minimal area) and end-diastole (maximal area), as depicted in [Figure 4]. Care must be taken to ensure that the endocardium is traced beneath the trabeculations along the free wall. RV FAC <35% is taken as cut off for RV systolic dysfunction., In patients with repaired TOF, studies have shown low to modest correlations between RVFAC and CMR-derived RV EF.,
|Figure 4: Echocardiogram in right ventricular focused apical four-chamber view showing calculation of right ventricular fractional area change, by tracing the endocardial border of right ventricular in end diastole and end systole. Panel a shows end diastolic area, and Panel b shows end systolic area|
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Tricuspid annular plane systolic excursion
It measures the maximal excursion distance of lateral TV annulus during RV systole. It is obtained from the apical four-chamber view using M mode [Figure 5]. It is based on the assumption that it reflects the global RV function, but it may not be true in patients with repaired TOF. In a study, which compared echocardiographic parameters with MRI-derived RVEF, it was seen that TAPSE had very poor correlation with MRI derived RVEF in 35 postoperated TOF patients. Age-related nomograms for TAPSE are available and are preferred over a single cut off.
|Figure 5: Tricuspid annular plane systolic excursion measured using M-mode at tricuspid annular plane in apical four-chamber view|
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The velocity of longitudinal motion of the tricuspid annulus as well as the RV basal-free wall is assessed by tissue Doppler (RV S' or RV systolic excursion velocity) [Figure 6]. According to the American Society of Echocardiography guidelines, S' <10 cm/sec by pulsed tissue Doppler is suggestive of RV systolic dysfunction. Doppler indices show correlation with CMR data.
|Figure 6: Tissue Doppler imaging at tricuspid annular plane showing systolic velocity S' >10 cm/s suggestive of normal right ventricular systolic function|
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The RV has a crescent shape with three different well-defined parts: The inflow, the outflow, and the apical region, all of which cannot be seen together at the same time using 2D imaging. 3D echocardiography images all these regions together as one unit and evaluates global RV volume and function. However, unlike LV assessment, a special software platform is required for RV 3D evaluation and it has a slightly longer learning curve. However, in experienced hands, it is recommended to use 3D volume and EF assessment. It has shown good correlation with CMR derived RV volumes and EF. The prognostic significance of 3D-echo-derived RVEF has also been studied, though not in repaired TOF patients.
Diastolic right ventricular function
The implications of diastolic dysfunction in patients with repaired TOF are not entirely clear. Some authors suggest that restrictive physiology of RV predicts superior exercise performance, but this finding has not been confirmed by others.,, In addition, this assessment by Doppler is susceptible to varying loading conditions. However, a combination of Doppler profile in the MPA (including late diastolic antegrade flow), right atrial dilatation, hepatic venous flow reversal, and changes in the caliber of the inferior vena cava with the respiratory cycle are useful clues about RV diastolic function in the absence of systolic dysfunction. The trans-tricuspid flow velocities should be measured at end-expiration and more than five consecutive beats should be averaged. A tricuspid E/A ratio <0.8 suggests impaired relaxation, and a tricuspid E/A ratio >2.1 with a deceleration time <120 msec suggests restrictive filling (particularly when accompanied by late diastolic forward flow into the MPA). However, similar threshold values have not been ascertained in patients with repaired TOF.
| Assessment of Pulmonary Valve Function|| |
Postoperated TOF patients either have native RVOT, or a TAP, or may have RV to PA conduit. Detailed assessment for PR and residual/recurrent RVOTO should be done. Young patients have good subcostal windows; hence, RVOT can be evaluated from this site. Both long-axis and short-axis planes should be evaluated. Transducer kept at 1–2 o'clock position produces a good inflow-outflow view of RV.
In older children and adults, parasternal long and short axis views facilitate assessment of RVOT. Assessment for the presence of RVOTO and its exact site (subvalvar, valvar, supravalvar MPA/branch PA) should be made. RVOT dimensions should be measured and aneurysm if present should be reported (aneurysm is thin walled and moves paradoxically as compared to rest of the ventricular-free wall). RV hypertrophy defined in adults as RV diastolic wall thickness > 5 mm should be reported. However, most postoperated TOF patients, have the infundibular-free wall composed of a patch, whose thickness might not be representative of RV hypertrophy in other parts of the chamber.
Assessment for pulmonary stenosis
When evaluating residual RVOT obstruction, identify the exact site of obstruction using color Doppler, pulsed-wave Doppler, and continuous-wave Doppler. In patients with RV-to-PA conduit, the obstruction can be at any location along the entire length of the conduit. It may or may not involve the origins of the PAs. The obstruction can be at one site or it may involve multiple sites. Color Doppler assessment indicates the site of obstruction by the occurrence of turbulence (mosaic pattern). Proximal obstruction masks/underestimates the distal obstruction.
The spectral Doppler flow profile helps in differentiating between dynamic obstruction within the RV cavity and residual fixed valvar or supravalvar stenosis. The dynamic obstruction has late peaking of the Doppler signal ("lobster claw” shape), whereas the fixed obstruction has midsystolic peaking. If multiple levels of obstructions in the RVOT and PAs are present, the contribution at each level is difficult to assess, especially when they are in close proximity. In older patients or in patients with RV-to-PA conduits, the branch PAs are sometimes difficult to assess for residual stenosis because of the high flow velocity within the conduit. A high TR jet velocity should prompt a careful search for RVOT or PA obstruction at some level.
Assessment for pulmonary regurgitation
PR is an important factor in the long-term outcomes of patients with repaired TOF. The pathophysiologic cascade that leads to RV dilatation and dysfunction has PR as the key initiating factor. This in turn has been linked to decreased exercise capacity, and increased risk for atrial and ventricular arrhythmias, as well as sudden cardiac death. Parasternal long- and short-axis views are used to evaluate for PR. PR jets are not easily seen by color Doppler in the RVOT. Unlike high pressure regurgitation jets such as TR/mitral regurgitation/aortic regurgitation, PR in postoperated TOF is low pressure. This “wide open/free” PR, has laminar flow with low velocity [Video 1] and [Video 2]. Therefore, the jet(s) may be overlooked by color Doppler. [Table 3] shows the qualitative and quantitative parameters for PR assessment.
|Table 3: Echocardiographic parameters indicating severe pulmonary regurgitation|
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Video 1: Color doppler imaging across main pulmonary artery and branch pulmonary arteries showing flow reversal in MPA as well as branch PAs suggestive of severe/free PR. The jet width of PR jet is almost equal to the RVOT diameter.
[Additional file 1]
Video 2: Color doppler imaging across main pulmonary artery and branch pulmonary arteries showing no flow reversal in MPA or branch PAs. The jet width of PR jet is very narrow suggestive of mild PR only.
[Additional file 2]
Validation studies of the severity of PR by echocardiography have compared Doppler parameters with the gold standard of CMR.,, Flow reversal in MPA happens in mild PR. In moderate PR, the flow reversal is seen in proximal branch PAs. In severe PR, the flow reversal occurs in distal branch PAs as well. When PR is severe, there is rapid equilibration of PA and RV pressure in diastole, hence deceleration time in the PR spectral Doppler signal is short [Figure 7] and [Figure 8]. Pressure half time is a useful parameter, but it might not be reliable in the presence of high RVEDP with ventricular dysfunction.
|Figure 7: Continuous wave Doppler imaging at pulmonary valve showing severe pulmonary regurgitation with short deceleration time. The pulmonary regurgitation trace touches baseline before the end of diastolic period|
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|Figure 8: Continuous wave Doppler imaging across the pulmonary valve showing less than severe pulmonary regurgitation, as indicated by a long deceleration time. The pulmonary regurgitation trace continues and touches baseline only at the end of diastolic period|
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Branch pulmonary arteries
Proximal branch PAs are seen from short-axis view. The supra-sternal and high left and right parasternal views are used to evaluate the mediastinal PAs, although it may be difficult sometimes in obese children or grown-up adults. RPA is visualized using a combination of views. The subcostal long-axis, high left parasternal short-axis, supra-sternal short-axis, and right parasternal short-axis views are helpful in visualizing the length of the RPA. LPA is visualized from high left parasternal short-axis and the supra-sternal long-axis views. The distal LPA is more difficult to visualize than the RPA because of the interface of air in the lung and the left bronchus.
The MPA is measured at its midpoint during systole. The diameters of the branch PAs are measured at the level of the origin. If stenosis is present, the narrowest diameter as well as the widest diameter of the vessel is reported. Type of stenosis, either discrete or long segment has to be reported. Significant stenosis in a branch PA is present if there is diastolic tailing of flow across it. Pandiastolic tailing is more significant than early or mid-diastolic tailing.
| Assessment for Residual Intra-Cardiac Shunts|| |
Ventricular septal defect/atrial septal defect
During intracardiac repair for TOF, VSD patch closure is done. However, in certain situations, apart from the large sub-aortic VSD, there are one/multiple additional muscular VSDs. Due to systemic right ventricle pressure in preoperative period, these additional defects may not be identified and not reported. In postoperative period, these defects now shunt left to right (as the PS has been relieved). They contribute to high pulmonary blood flow and pulmonary edema if the left to right shunt is significant. Sometimes, the defects are not large, and do not cause significant left to right shunt. In these situations, they just produce pansystolic murmur and are not hemodynamically significant. The other types of VSDs are the residual VSD, which are near the patch of the large subaortic VSD. These are either present from the time of surgery due to lack of complete circumferential suturing of the patch, or they develop over time due to the patch giving way. They are particularly common at the superior portion of the patch.
The integrity of the VSD patch is determined by two-dimensional imaging and color Doppler flow mapping. The size and location of the VSD should be assessed on the subcostal and parasternal views to assess for suitability for device closure. The gradient across the VSD gives an estimate of the RV systolic pressure. Similarly, the atrial septum is examined by color Doppler for the presence of a patent foramen ovale or a secundum atrial septal defect.
| Aortic Regurgitation and Ascending Aortic Dilation|| |
Some patients with TOF have aortopathy. Dilatation of the aortic root is common in adults with repaired TOF, particularly in those with prior shunts and those with late repair. Measurements of the aortic root is accomplished from the parasternal long-axis view. Imaging from the right parasternal window can facilitate depiction and measurements of the proximal and mid ascending aorta. Measurements are made using 2D imaging according to published guidelines in CHD during maximal expansion (mid to late systole). The measurement of internal diameter is the current standard.
| Assessment for Left Ventricle Function|| |
LV function assessment is important because LV systolic dysfunction has been shown to be an important prognostic marker for premature death in patients with repaired TOF.,, RV dilatation and dysfunction in patients with repaired TOF adversely affect LV geometry and function. RV dilatation can produce D-shaped LV, which can interfere with its diastolic filling. Unfavorable ventriculo-ventricular interaction can cause worsening of LV function in the presence of RV dilatation and dysfunction., Due to marked RV dilatation, the right ventricle is often apex forming. Therefore, adjustment of the transducer position in the apical view is required to avoid foreshortening of the LV.
The size, global function, and regional wall motion of the LV are determined from multiple views. The measurement of LV systolic function by shortening fraction assumes a circular geometry with homogeneous contraction, conditions that are seldom met in patients with repaired TOF. Measurements of LV volumes and EF by 3D echocardiography are preferred over 2D measurements. Given that most patients with repaired TOF reach adulthood and the average age of this population continues to increase, the risk for the development of acquired ischemic heart disease is likely to increase. Therefore, stress echocardiography may play an increasing role in this population.,
| Conclusion|| |
It is very important to study the postoperated TOF patient's heart in detail. A step-by-step evaluation of all structures is carried out. Maximum hemodynamic data as far as possible should be extracted using echocardiography. This may further guide the need of other investigations, if an intervention is required.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]