Introduction
Single-ventricle patients with elevated pulmonary vascular resistance (PVR) or end-diastolic pressure (EDP) are excluded from undergoing total cavopulmonary connection (TCPC). However, a subset of patients deemed to be at acceptable risk experience prolonged length of stay (LOS) after TCPC. Routine assessment of ventricular function has been inadequate in identifying these high-risk patients. Speckle-tracking echocardiography (STE) is a novel method for assessment of myocardial deformation that may be useful in single-ventricle patients. The aim of this study was to perform a contemporary preoperative risk assessment for prolonged LOS to determine whether STE improves risk stratification before TCPC.
Methods
Our single institution’s perioperative data were retrospectively collected. The primary outcome was postoperative LOS >14 days. Longitudinal and circumferential STE deformation measures were analyzed on echocardiograms obtained during preoperative catheterization. Patient-specific, echocardiographic, and catheterization data were included in multivariable logistic regression. Receiver operating characteristic area under the curves (AUC) were analyzed.
Results
From 2007 to 2014, 135 patients who underwent TCPC were included in the analysis. The median LOS was 11 (IQR 9-14) days. The PVR ( P < .01) and circumferential strain rate (CSR) ( P < .01) were the only variables independently associated with LOS >14 days. For every 0.1 s −1 CSR increased, there was a 20% increased odds of prolonged LOS. The AUC for CSR was 0.70. The AUC for PVR and EDP combined was 0.68. The AUC for PVR, EDP, and CSR combined was 0.73.
Conclusion
Preoperative CSR is independently associated with LOS >14 days and improves preoperative risk stratification in patients undergoing TCPC.
Highlights
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Echocardiography has had a limited role in risk stratifying patients undergoing total cavopulmonary connection.
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Our aim is to investigate the association between measures of myocardial deformation and postoperative length of stay after total cavopulmonary connection.
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Preoperative circumferential strain rate was associated with length of stay >14 days.
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Circumferential strain rate improved preoperative risk stratification in these patients.
The current management strategy for children with single-ventricle physiology is staged surgical palliation, ultimately leading to total cavopulmonary connection (TCPC) circulation. This circulation requires blood to flow passively from the cavae directly through the pulmonary arteries to the heart. Ventricular dysfunction in the systemic ventricle often translates to the development of heart failure and resultant inefficiency within the TCPC pathway, which increases the risk for significant postoperative morbidity, early surgical palliation failure, and death.
Preoperative risk assessment before TCPC often includes invasively derived indices of pulmonary vascular resistance and end-diastolic pressure in the catheterization laboratory. Patients with significantly abnormal pulmonary vascular resistance or end-diastolic pressure do not undergo TCPC to avoid the morbidity and mortality associated with the resultant suboptimal hemodynamics after the operation. Even so, a subset of patients continue to experience significant morbidity, including prolonged hospital length of stay (LOS), after TCPC. Identifying these at-risk patients has been difficult. Anecdotal evidence suggests that those with poor ventricular function experience prolonged LOS after TCPC. However, including ventricular function in the preoperative risk assessment has been challenging because the echocardiographic assessment of ventricular function in single-ventricle physiology is frequently qualitative, with poor reproducibility. The quantitative assessment of single-ventricular function is difficult because of complex and heterogenous ventricular geometry. Owing to these challenges, several studies in the modern era have not included echocardiographic measures of ventricular function in their analyses of preoperative risk assessment. When included in risk models, qualitative echocardiographic measures have shown no value in predicting LOS after TCPC.
Speckle-tracking echocardiography (STE) is an attractive tool for use in the assessment of ventricular function in single-ventricle physiology because of its angle independence, geometry independence, and reproducibility. It has been shown to be more sensitive in detecting changes in ventricular function in children and adults with heart disease than more conventional measures, such as ejection fraction. However, no studies investigating the clinical usefulness of STE in predicting post-TCPC outcomes in single-ventricle patients have been performed. The aims of this study were to (1) investigate the association between preoperative measures of myocardial deformation and postoperative LOS after TCPC and (2) determine whether these STE measures of ventricular function improve risk stratification before TCPC over conventional risk factors obtained during invasive cardiac catheterization.
Methods
This was a retrospective analysis of patients with single-ventricle physiology who underwent TCPC at the Medical University of South Carolina from 2007 to 2014. To standardize echocardiographic analysis, patients without a clearly dominant ventricle were excluded. Preoperative catheterization data were abstracted from the patient record. Perioperative data included those variables which were reported to the Society of Thoracic Surgeon’s database (all variables listed in Table 1 ). The primary outcome was postoperative LOS >14 days, which represented the top quartile. This study was reviewed and approved by the Medical University of South Carolina’s Institutional Review Board.
| Variable | LOS ≤14 days ( n = 102) | LOS >14 days ( n = 33) | P value |
|---|---|---|---|
| Age (y) | 4.0 (3.2, 4.6) | 4.5 (3.6, 5.7) | .08 |
| Male, n (%) | 56 (55%) | 21 (63%) | .51 |
| Height (cm) | 98 (94, 103) | 101 (94, 110) | .23 |
| Weight (kg) | 15.0 (14.1, 16.2) | 15.2 (13.5, 16.8) | .98 |
| SBP (mm Hg) | 89 ± 13 | 82 ± 10 | .01 |
| DBP (mm Hg) | 45 (40, 50) | 42 (40, 47) | .49 |
| CPB time (min) | 109 (91, 142) | 118 (96, 151) | .61 |
| End diastolic pressure (mm Hg) | 7 (6, 9) | 8 (7, 9) | .03 |
| Transpulmonary gradient (mm Hg) | 4 (3, 5) | 4 (4, 6) | .41 |
| Rp (Wood units) | 1.6 (1.2, 2.0) | 2.0 (1.4, 2.3) | .07 |
| A-V O 2 saturation difference (%) | 17 (14, 20) | 17 (15, 21) | .49 |
| Right ventricular dominance, n (%) | 60 (59%) | 23 (70%) | .28 |
| Presence of aorto-pulmonary collaterals, n (%) | .80 | ||
| None | 22 (21%) | 5 (15%) | |
| Small | 66 (65%) | 23 (70%) | |
| Large, coiled | 14 (14%) | 5 (15%) | |
| Atrioventricular valve regurgitation grade, n (%) | .04 | ||
| None–Trivial | 18 (17%) | 1 (3%) | |
| Mild | 75 (74%) | 25 (76%) | |
| Moderate | 8 (8%) | 6 (18%) | |
| Severe | 1 (1%) | 1 (3%) | |
| Fractional area change (%) | 24.1 (18.4, 31.1) | 22.1 (14.6, 29.4) | .28 |
| SAPSE (cm) | 0.60 (0.40, 0.80) | 0.60 (0.43, 0.78) | .89 |
| Ejection fraction (%) | 43.4 ± 7.7 | 41.1 ± 10.6 | .18 |
| Longitudinal strain (%) | −15.4 ± 3.2 | −14.7 ± 4.4 | .97 |
| Longitudinal strain rate (s −1 ) | −1.08 (−1.24, −0.90) | −1.07 (−1.30, −0.75) | .78 |
| Longitudinal EDSR (s −1 ) | 1.21 (1.01, 1.45) | 1.17 (0.89, 1.49) | .50 |
| Circumferential strain (%) | −13.8 (−16.3, −11.4) | −11.9 (−14.7, −9.8) | .04 |
| Circumferential strain rate (s −1 ) | −1.05 (−1.27, -0.89) | -0.97 (−1.14, −0.61) | .02 |
| Circumferential EDSR (s −1 ) | 1.06 (0.84, 1.29) | 0.72 (0.65, 1.21) | .05 |
Echocardiographic Analysis
All echocardiographic studies were performed using a Phillips 7500 or IE33 ultrasound system (Andover, MA). All studies were performed with the patients under general anesthesia immediately before cardiac catheterization, as is the institutional routine. Echocardiograms were stored in Digital Imaging and Communications in Medicine format at a frame rate of 30 frames/sec. Echocardiograms were analyzed retrospectively by a single blinded reviewer.
Conventional parameters for assessment of single-ventricular function from the apical four-chamber view included (1) 2D single-ventricle annular plane systolic excursion measured as the difference in length from the lateral free wall of the dominant ventricle at the level of the atrioventricular valve to the apex in diastole versus systole and (2) 2D fractional area change (FAC) calculated as (end-diastolic area − end-systolic area)/end-diastolic area of the dominant ventricle. Qualitative assessments of atrioventricular valve regurgitation and ventricular function were also recorded.
Speckle-tracking echocardiography was performed retrospectively on images stored for offline analysis using vendor independent software (Cardiac Performance Analysis version 3.0; Tomtec, Hamden, CT). The endocardial border was manually traced, and tracking was automatically performed by the software ( Figure 1 ). Segments with inadequate tracking were excluded from the analysis. Global measures of longitudinal or circumferential deformation were excluded if >2 segments displayed inadequate tracking. Six segments from the apical four-chamber view were averaged to measure longitudinal strain, strain rate, and early diastolic strain rate. From this view, the software automatically calculates ejection fraction using the single-plane Simpson’s method. Six segments from the parasternal short-axis view below the level of the atrioventricular valve(s) at the midventricular level were averaged to calculate circumferential strain, strain rate, and early diastolic strain rate. A more negative systolic strain or strain rate indicates better ventricular function.
Statistical Analysis
The distribution of data as parametric or non-parametric was assessed using the Shapiro-Wilk test. Differences between patients with and without prolonged LOS were assessed using independent t tests or Mann-Whitney U tests as appropriate for continuous variables and χ 2 test or Fisher’s exact test for categorical variables. Univariate logistic regression was performed to assess the relationship between independent variables and postoperative LOS >14 days. Multivariable regression was then performed, including independent variables that displayed a P value of <0.20 upon univariable analysis. Multivariable logistic regression was performed using stepwise elimination, excluding independent variables with a P value >.10 or those that did not significantly improve the explanatory power of the model (improvement in the Nagelkerke R 2 value by .03 or more). Receiver operating characteristic curves and associated c -statistics were calculated to determine the discriminatory power of independent variables in predicting the primary outcome. Missing data in the regression analysis were imputed using the chained equations method over five imputations, and pooled results are reported. This method operates under the assumption that given the variables used in the imputation procedure, the missing data are missing at random. In the procedure a series of regression models are run whereby each variable with missing data is modeled conditional on the other variables in the data. This means that each variable can be modeled according to its distribution, with, for example, binary variables modeled using logistic regression and continuous variables modeled using linear regression. The analyses of multiply imputed data take into account the uncertainty in the imputations and yield accurate standard errors. Interobserver variability in speckle-tracking measures of myocardial deformation were assessed using intraclass correlation coefficients (ICC) of absolute agreement in 20% of studies. A P value of <.05 was considered statistically significant. All statistics were performed using IBM SPSS version 23 (Armonk, NY).
Results
From 2007 to 2014, 141 patients underwent TCPC. Of those, six were excluded because ventricular dominance could not be clearly identified. All remaining 135 patients were included in the analysis. Extracardiac conduits were performed in 123 patients (91%). Creation of a fenestration between the TCPC and the atrium was performed in 120 patients (89%). In general, fenestrations were not created if patients had evidence of pulmonary arteriovenous malformations on preoperative catheterization. Right ventricular dominance was present in 83 patients (61%). The median LOS in the entire cohort was 11 days (IQR 9, 14). Thirty-three patients (24%) had a LOS >14 days. The 30-day mortality was 0%. Four patients (3%) were intubated >1 day. Subject demographics, preoperative echocardiographic and catheterization data, perioperative data, and comparisons between patients with LOS ≤14 days and >14 days can be found in Table 1 .
There were no differences in LOS between patients of left versus right dominant ventricular morphology: 10 (IQR 9-12) days versus 11 (IQR 9-15) days, respectively ( P = .41). There were no differences in demographic, echocardiographic, catheterization, or perioperative data in patients with left versus right ventricular dominant morphology ( Table 2 ) with the exception of increased severity of atrioventricular valve regurgitation in those with right ventricular morphology ( P < .01).
