In normal pediatric echocardiograms, the distance from the junction of superior vena cava (SVC) and right atrium to inferior vena cava (IVC) and right atrium is linearly related to height. We examine this relation in children listed for heart transplant with idiopathic dilated cardiomyopathy (IDC) compared with the previously defined normal distribution of SVC-IVC to improve matching of heart sizes. Measurements of SVC-IVC and left ventricular end-diastolic diameter in 55 pediatric patients with IDC were correlated with height, weight, and body surface area. Regression analyses were performed to find the best-fit equation and correlation coefficient. Generalized linear modeling compared SVC-IVC in patients with IDC with normal SVC-IVC values from 254 patients. There was a strong linear relation in patients with IDC between SVC-IVC and height (R 2 = 0.84) and a logarithmic relation to weight (R 2 = 0.80). Left ventricular end-diastolic diameter did not correlate with SVC-IVC or any other parameter. In 87% of patients with IDC, SVC-IVC was over 2 SDs above predicted normal values (mean z-score = 4.3 ± 2.1). In conclusion, predicted SVC-IVC in patients with IDC was different from published norms (p <0.001). SVC-IVC in pediatric patients with IDC, although linearly related to height, is consistently above normal values.
Ultimately, most children with end-stage idiopathic dilated cardiomyopathy (IDC) will face a major challenge in pediatric transplantation: waiting for a size-appropriate organ. Presently, most pediatric centers size-match donors to recipients based on weight. Donor weight is used as a surrogate for donor organ size, as a donor heart that is either too large or too small may lead to increased morbidities, if not mortality. The echocardiographic measurement most commonly used to estimate heart size is left ventricular end-diastolic diameter (LVEDd). However, given studies reporting the benefits of bicaval anastomosis for orthotopic heart transplantation (OHT), we recently investigated the “height” of the donor heart, or the distance from the junction of the superior vena cava and right atrium to the inferior vena cava and right atrium (SVC-IVC), as a better predictor of heart size. We found that in children without heart disease, SVC-IVC is linearly related to height; thus, the height (or size) of the normal heart most closely correlates with overall height. The applicability of this measurement in children with cardiomyopathy is unknown. Therefore, in this study, our objective was to investigate SVC-IVC in children with IDC listed for OHT. We hypothesized that this measurement was more closely related to height than weight in IDC.
Methods
After approval was obtained from the Columbia University Institutional Review Board, a retrospective analysis was performed of all patients with IDC who underwent OHT at our institution between December 2005 and July 2012. Echocardiographic measurements of SVC-IVC and LVEDd were performed on the last echocardiogram within 3 months of transplant. Demographic data collected from the time of the echocardiogram included age, sex, height, weight, and body surface area (BSA) as calculated by the Haycock formula.
Echocardiographic clips were included if 3 separate measurements of SVC-IVC were obtainable from 3 separate beats in the subxiphoid short-axis view ( Figure 1 ). Two reviewers (E.H. and W.Z.) measured SVC-IVC 3 times each in the subxiphoid short-axis view and repeated these measurements in a second echocardiographic clip. Highest and lowest values were discarded, and the mean SVC-IVC was calculated for each individual. Three measurements of LVEDd were performed on 3 separate beats in the parasternal short-axis M-mode view, and mean LVEDd was calculated in similar fashion.
Data analysis was performed using Excel 2010 (Microsoft Corp, Redmond, Washington) and SPSS, version 19 (IBM Corp, Armonk, New York). Inter-rater reliability analysis was performed for the 2 separate measurements made by 2 reviewers. Correlation with demographic variables was analyzed for each of the measurements. The best-fit curve and Pearson’s correlation coefficient were calculated for all comparisons. Generalized linear modeling compared the ultimate predictive model for IDC with previously published normal SVC-IVC values.
Given a strong correlation between SVC-IVC and height in patients with IDC, a finding similar to our experience with normal patients, we then sought to further characterize the relation between this distance in patients with IDC and normal echocardiograms. Using the equation from the best-fit line as reported by Zuckerman et al in normal patients (y = 0.0332x + 0.5834, R 2 = 0.904, where x = height and y = SVC-IVC distance), we derived a normal SVC-IVC value based on the heights of our patients with IDC. Using 95% confidence intervals and the difference between IDC and normal values, we calculated the SD of SVC-IVC in patients with IDC and then calculated z-scores. We also calculated LVEDd z-scores for further comparison.
Results
Sixty-five patients met inclusion criteria. Ten patients (15%) were excluded due to poor imaging or the absence of an adequate subxiphoid view. Fifty-five echocardiograms were deemed acceptable for analysis. The individuals were aged 2 months to 19 years (median age 7.8 years). Of the 55 individuals, 21 (38%) were women, and 34 (62%) were men; 11 (20%) were <1-year-old, 20 (36%) were between 1-year-old and 10-years-old, and 24 (44%) were >10-years-old. Nine patients (16%) exhibited features of left ventricular noncompaction on echocardiogram.
SVC-IVC was highly reproducible between 2 observers (R 2 = 0.91). To correlate SVC-IVC and LVEDd with demographic variables, they were plotted against height, weight, age, and BSA to determine a best-fit curve and Pearson’s correlation coefficient. In patients with IDC, there was a strong linear relation between SVC-IVC and height (R 2 = 0.84; Figure 2 ) and between SVC-IVC and age (R 2 = 0.84). The relations between SVC-IVC and weight (R 2 = 0.80; Figure 2 ) and between SVC-IVC and BSA (R 2 = 0.82) were logarithmic. LVEDd did not correlate as strongly with height (R 2 = 0.66; Figure 3 ), weight (R 2 = 0.64; Figure 3 ), BSA (R 2 = 0.65), or age (R 2 = 0.6) in patients with IDC. There was not a strong correlation between LVEDd and SVC-IVC (R 2 = 0.58; Figure 4 ).
