Background
Congenitally corrected transposition of the great arteries is a rare form of congenital heart disease. Management is controversial; options include observation, physiologic repair, and anatomic repair. Assessment of morphologic left ventricle preparedness is key in timing anatomic repair. This study’s purpose was to review the modalities used to assess the morphologic left ventricle preoperatively and to determine if any echocardiographic variables are associated with outcomes.
Methods
A retrospective review of patients with congenitally corrected transposition of the great arteries eligible for anatomic repair at Lucile Packard Children’s Hospital from 2000 to 2016 was conducted. Inclusion criteria were (1) presurgical echocardiography, magnetic resonance imaging, and cardiac catheterization and (2) clinical follow-up information. Echocardiographic measurements included left ventricular (LV) single-plane Simpson’s ejection fraction, LV eccentricity index, LV posterior wall thickening, pulmonary artery band (PAB)/LV outflow tract (LVOT) pressure gradient, and LV and right ventricular strain. Magnetic resonance imaging measurements included LV mass, ejection fraction, eccentricity index, and LV thickening. LV pressure, PAB/LVOT gradient, right ventricular pressure, pulmonary vascular resistance, and Qp/Qs constituted catheterization data. Outcomes included achieving anatomic repair within 1 year of assessment in patients with LVOT obstruction or within 1 year of pulmonary artery banding and freedom from death, transplantation, or heart failure at last follow-up.
Results
Forty-one patients met the inclusion criteria. PAB/LVOT gradients of 85.2 ± 23.4 versus 64.0 ± 32.1 mm Hg ( P = .0282) by echocardiography and 60.1 ± 19.4 versus 35.9 ± 18.9 mm Hg ( P = .0030) by catheterization were associated with achieving anatomic repair and freedom from death, transplantation, and heart failure. Echocardiographic LV posterior wall thickening of 35.4 ± 19.8% versus 20.6 ± 15.0% ( P = .0017) and MRI LV septal wall thickening of 37.1 ± 18.8% versus 19.3 ± 18.8% ( P = .0306) were associated with achieving anatomic repair. Inter- and intraobserver variability for echocardiographic measurements was very good.
Conclusions
PAB/LVOT gradient and LV posterior wall thickening are highly reproducible echocardiographic measurements that reflect morphologic LV performance and can be used in assessing patients with congenitally corrected transposition of the great arteries undergoing anatomic repair.
Highlights
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The authors assessed imaging techniques in patients with CCTGA.
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Echocardiography was an important tool for assessing the morphologic left ventricle before anatomic repair.
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Intrinsic or PAB-associated LVOT gradient was a useful measurement of LV preparedness for anatomic repair.
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LVPW thickening was also useful in assessing the left ventricle before anatomic repair.
Congenitally corrected transposition of the great arteries (CCTGA) is a rare form of congenital heart disease with an incidence of one in 33,000 live births, accounting for 0.5% of all congenital heart malformations. CCTGA is characterized by double discordance, a combination of atrioventricular and ventriculoarterial discordance. Presentation in these patients is variable, and symptoms may be secondary to associated malformations, heart block, or systemic right ventricular (RV) failure. Management of this patient population is also variable, with some advocating physiologic repair and others preferring anatomic correction to avoid the anticipated long-term dysfunction of the systemic right ventricle. Success of anatomic repair is dependent on the morphologic left ventricle being prepared to sustain the systemic circulation. Training of the morphologic left ventricle is therefore necessary and has been achieved by temporary banding of the pulmonary artery to increase the left ventricular (LV) afterload in the absence of adequate pulmonary outflow tract obstruction. Assessment of LV preparedness has been used to determine the timing of anatomic repair, although exact indications and selection criteria remain controversial. At present there is no established imaging standard for determining LV preparedness, because of the rarity of the cardiac lesion as well as center-specific approaches. Cardiac magnetic resonance imaging (MRI) is commonly used to assess the adequacy of the morphologic left ventricle in patients with CCTGA. MRI allows quantification of morphologic LV mass and function. Cardiac catheterization has been used to obtain useful hemodynamic parameters. Echocardiography is commonly used for the assessment of LV structure and function. The abnormal position of the morphologic left ventricle in CCTGA, however, makes conventional methods of echocardiographic evaluation challenging.
The purpose of this study was to review the various modalities used to assess LV preparedness before anatomic repair. This includes echocardiography, MRI, and cardiac catheterization. In addition, we sought to determine the utility of echocardiography as a modality to evaluate the morphologic left ventricle and enhance our understanding of LV mechanics in patients with CCTGA undergoing anatomic repair.
Methods
Patient Population
A retrospective review of patients with CCTGA, eligible for anatomic repair, at Lucile Packard Children’s Hospital, Stanford University, between 2000 and 2016 was conducted. Anatomic repair was defined as (1) the double-switch operation, which combines an atrial baffle procedure with an arterial switch operation or combines hemi-Mustard, Glenn, and arterial switch procedures in patients without LV outflow obstruction, or (2) an atrial baffle procedure combined with a Rastelli procedure in patients with ventricular septal defects (VSDs) and LV outflow tract (LVOT) obstruction. Patients were identified from the echocardiography database using Syngo Dynamics workstation (Siemens Medical Solutions USA, Mountain View, CA; Syngo Dynamics Solutions, Ann Arbor, MI) and a prospectively maintained surgical database. Inclusion criteria were (1) a diagnosis of CCTGA, (2) availability of preanatomic repair echocardiographic and magnetic resonance images as well as cardiac catheterization data, and (3) availability of clinical follow-up information. Patients were excluded if CCTGA anatomy precluded anatomic repair and necessitated single-ventricle palliation, imaging was inadequate, or patients were lost to follow-up. The study was approved by the Stanford University institutional review board.
Preanatomic Repair Assessment
Criteria used at our center to determine suitability for anatomic repair are based on echocardiographic, cardiac catheterization, and MRI data. This includes (1) normal LV function and mitral valve function by echocardiography, (2) near systemic LV pressure by cardiac catheterization, and (3) achievement of normal LV mass by cardiac MRI.
Echocardiography
All echocardiographic images were acquired on the Siemens Sequoia C512 (Siemens Medical Solutions) or the Philips iE33 (Philips Medical Systems, Bothell, WA). Postprocessing of echocardiographic images was performed by a single investigator to obtain measurements of morphologic LV structure and function. Measurements included eccentricity index, single-plane Simpson’s LV ejection fraction (LVEF), LV posterior wall (LVPW) dimensions, continuous-wave Doppler–derived pulmonary artery band (PAB)/LVOT pressure gradient, and LV and RV strain measurements. Eccentricity index was measured during systole as the ratio of the septolateral distance (D1) and anteroposterior distance (D2) ( Figure 1 ). Two dimensional tracing of the LV endocardial surface in the apical four-chamber view during systole and diastole was done to determine morphologic LV single-plane function using Simpson’s method of disks. Because two-chamber views of the morphologic left ventricle were not recorded or not possible to obtain, biplane Simpson’s measurements could not be performed. In the parasternal view, two-dimensional measurements were taken of the LVPW using an extension of the line D2 ( Figure 1 ) during diastole and systole. The LVPW systolic-to-diastolic ratio was then calculated to establish thickening. The highest and mean PAB/LVOT gradient by continuous-wave Doppler was determined ( Figure 2 ). Postprocessing using Syngo Velocity Vector Imaging 3.0 software (Siemens Medical Solutions USA), compatible with both the Philips iE33 and Siemens Sequoia C512 ultrasound machines, was used to calculate LV strain. This was performed on echocardiographic loops from the parasternal short-axis view and four-chamber apical view to obtain longitudinal, radial, and circumferential systolic strain imaging of the morphologic left ventricle. Two- and three-chamber apical views of the morphologic left ventricle were not recorded or possible to obtain and were therefore not available for strain analysis. Subsequently, the LV free wall was also assessed by obtaining deformation analysis with exclusion of the interventricular septum. In addition, deformation of the right ventricle, to assess for ventricular-ventricular interaction, was also performed using imaging from the parasternal short-axis view and the apical two-, three-, and four-chamber views when available.
Magnetic Resonance Imaging
The indication for all cardiac MRI studies was to establish LVEF and LV mass. MRI reports were reviewed for measurements of morphologic LV mass (indexed to body surface area) and short-axis stack–derived morphologic LV function. Postprocessing was performed by a single observer to obtain measurements of LV wall thickening in the short axis ( Figure 3 ) as well as systolic and diastolic eccentricity index.
Cardiac Catheterization Data
Cardiac catheterization was performed in patients before completing anatomic repair to obtain hemodynamic data. Relevant measurements included morphologic LV systolic and diastolic pressure, the PAB or LVOT peak-to-peak gradient, pulmonary vascular resistance, and Qp/Qs. A ratio of LV to RV systolic pressure was calculated.
Outcomes
Patients’ medical records were reviewed for surgical procedures and postsurgical outcomes, including (1) achieving anatomic repair within 1 year of assessment in patients with adequate intrinsic LVOT obstruction or within 1 year of PAB in those without adequate intrinsic LVOT obstruction and (2) achieving anatomic repair with freedom from death, cardiac transplantation, and congestive heart failure at last follow-up. Adequate LVOT obstruction was defined as near systemic-level LV pressure. Congestive heart failure diagnosis was based on documentation of clinical symptoms and need for heart failure medication.
Statistical Analysis
All statistical calculations were performed in SAS Enterprise Guide version 4.2 (SAS Institute, Cary, NC) and Analyze-it Standard version 3.20.2 (Leeds, United Kingdom). Student’s t test was used to assess imaging variables predicting outcomes. As age was not normally distributed, nonparametric testing (Wilcoxon two-sample test) was used for assessment. Receiver operating characteristic curves were generated to determine the associations of variables with outcomes. Because the presence of a VSD may influence Doppler measurements, LVOT/PAB peak pressure gradient measurements were compared in patients with and without VSDs. A Fisher exact test was implemented to determine if a VSD had any bearing on outcomes. Subanalysis of patients who underwent pulmonary artery banding training was also performed. Reproducibility was tested in a random sample of 15 subjects, with the same investigator and a second investigator measuring PAB/LVOT gradient and LVPW systolic-to-diastolic ratio to determine intra- and interobserver variability. A Delong comparison was performed to assess different methods of LV measurement when associated with outcomes. P values < .05 were considered to indicate statistical significance.
Results
Patient Population
Seventy-seven patients were identified as potential participants for the study. Thirty-six patients were excluded because of anatomy precluding anatomic repair or inadequate imaging available. Therefore, 41 patients were eligible for the study ( Table 1 ). The anatomic subtypes included 20 patients with CCTGA and intact ventricular septum, three of who had concomitant intrinsic LVOT obstruction. Twenty-three patients had CCTGA with VSDs, with eight of these patients having intrinsic LVOT obstruction. Other associated defects included Ebstein’s anomaly in seven patients, pulmonary atresia in two, dextrocardia in two, situs inversus in one, right atrial isomerism and total anomalous pulmonary venous return in one, and congenital heart block requiring pacing in five. Twenty-eight of the 41 patients included in the study underwent PAB for LV training. The remaining 13 patients of the cohort were deemed to have adequate LV preparedness. Overall outcomes were good, with 71% of patients (29 of 41) achieving anatomic repair. One death was reported, in a patient following cardiac transplantation. The transplantation occurred remote to the anatomic repair, 15 months later, and death occurred 17 months after transplant and was therefore attributed to post-transplantation complications rather than anatomic repair for CCTGA. Mean follow-up time for the cohort was 8 months (range, 0–90 months).
| Variable | Value |
|---|---|
| Gender (female) | 19 |
| Age (y) | 6.4 ± 7.3 |
| Body surface area (m 2 ) | 0.81 ± 0.50 |
| SBP (mm Hg) | 100 ± 17 |
| DBP (mm Hg) | 59.7 ± 12.8 |
| Anatomic repair achieved | 29/41 |
| Congestive heart failure | 12/41 |
| Death | 0/41 |
| Transplantation | 1/41 |
Associations with Clinical Outcomes
All imaging variables were assessed for associations with clinical outcomes ( Table 2 ). Echocardiography-derived LVPW systolic-to-diastolic ratio, which is the change in LVPW thickness from diastole to systole, was significantly associated with outcomes. LVPW thickening of 35.4 ± 19.8% versus 20.6 ± 15.0% ( P = .0017) was associated with achieving anatomic repair, but was not associated with freedom from death, transplantation, or heart failure at last follow-up. LV septal wall thickening measured by MRI was also associated with achieving anatomic repair (37.1 ± 18.8% vs 19.3 ± 18.8%, P = .0306) and with freedom from death, transplantation, and heart failure (38.2 ± 18.9% vs 20.6 ± 18.1%, P = .0218). Echocardiography-derived LV wall thickening and MRI-derived LV wall thickening measurements did not correlate, which may be due to different regions of the left ventricle being measured. PAB/LVOT gradient derived by echocardiography and catheterization was associated with both achieving anatomic repair and achieving anatomic repair with freedom from death, transplantation, and congestive heart failure at last follow-up (85.2 ± 23.4 vs 64.0 ± 32.1 mm Hg [ P = .0282] by echocardiography and 60.1 ± 19.4 vs 35.9 ± 18.9 mm Hg [ P = .0030] by catheterization). LV systolic pressure and pulmonary vascular resistance by catheterization were also associated with achieving anatomic repair. Therefore, variables assessed by multiple modalities were found to be significant in their associations with outcomes ( Figures 4 and 5 ). Age was not associated with outcomes (not successful median age of 5.8 years and successful median age of 2.4 years, P = .4030). Echocardiography-derived systolic eccentricity index, LVPW Z score, LV and RV strain, MRI LVEF and LV mass, and MRI diastolic and systolic eccentricity index were all not associated with outcomes. Intra- and interobserver variability was excellent for PAB/LVOT gradient (intraclass correlation coefficient = 0.99 and 0.98, respectively) and good for LVPW measurements (intraclass correlation coefficient = 0.72 and 0.60, respectively). Peak and mean PAB/LVOT gradient by echocardiography roughly correlated with peak-to-peak cardiac catheterization–derived measurements ( r = 0.55 [ P < .0023] and r = 0.60 [ P = .0007], respectively). A Delong comparison of different methods of assessment was performed, and no statistical difference was found.
| Variable | Anatomic repair (yes) ( n = 29) | Anatomic repair (no) ( n = 12) | P |
|---|---|---|---|
| Single-plane Simpson’s LVEF (%) | 48.4 ± 9.4 | 46.4 ± 10.3 | .5879 |
| LVPW thickening (%) | 35.4 ± 19.8 | 20.6 ± 15.0 | .0017 ∗ |
| LVPW Z score | 0.38 ± 2.0 | 0.63 ± 1.7 | .7806 |
| Echo PAB/LVOT gradient (mm Hg) | 85.2 ± 23.4 | 64.0 ± 32.1 | .0282 ∗ |
| Echo LV systolic eccentricity index | 0.63 ± 0.30 | 0.76 ± 0.56 | .4428 |
| LV four-chamber global longitudinal strain (%) | −16.8 ± 5.3 | −18.3 ± 4.9 | .4448 |
| LV global radial strain (%) | 14.4 ± 7.0 | 11.5 ± 6.6 | .2640 |
| LV global circumference strain (%) | −14.8 ± 5.6 | −11.8 ± 4.3 | .1349 |
| LV four-chamber free wall longitudinal strain (%) | −19.8 ± 7.2 | −22.8 ± 7.7 | .2772 |
| LV free wall radial strain (%) | 15.4 ± 13.6 | 10.8 ± 4.5 | .1506 |
| LV free wall circumferential strain (%) | −14.9 ± 8.4 | −10.5 ± 5.1 | .0759 |
| RV longitudinal strain (%) | −16.6 ± 5.9 | −12.5 ± 5.6 | .0667 |
| MRI LVEF (%) | 63.2 ± 9.0 | 65.1 ± 6.6 | .5723 |
| MRI LV mass in systole (g) | 49.1 ± 4.4 | 35.9 ± 11.7 | .1054 |
| MRI LV mass in diastole (g) | 48.0 ± 15.8 | 38.3 ± 10.3 | .1040 |
| MRI LV septal wall thickening (%) | 37.1 ± 18.8 | 19.3 ± 18.8 | .0306 ∗ |
| MRI systolic eccentricity index | 2.2 ± 1.5 | 1.9 ± 0.6 | .9256 |
| MRI diastolic eccentricity index | 1.6 ± 0.5 | 1.5 ± 0.3 | .7097 |
| Catheterization LV systolic pressure (mm Hg) | 84.9 ± 17.1 | 59.4 ± 17.7 | .0006 ∗ |
| Catheterization LV diastolic pressure (mm Hg) | 8.1 ± 3.3 | 6.9 ± 3.1 | .3246 |
| Catheterization PAB/LVOT gradient (mm Hg) | 60.1 ± 19.4 | 35.9 ± 18.9 | .0030 ∗ |
| Catheterization Qp/Qs ratio | 1.1 ± 0.42 | 1.1 ± 0.22 | .9301 |
| Pulmonary vascular resistance (Wood units) | 2.3 ± 1.06 | 1.3 ± 0.60 | .0114 ∗ |
| Catheterization LV/RV systolic pressure ratio | 101.0 ± 17.8 | 84.7 ± 17.2 | .2281 |
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