Assessment of Right Ventricular Volume in Pediatric Patients - Is Apical or Subcostal Window More Accurate?

RVEDV measured by the subcostal window is more accurate than RV volume measured in the apical window in a cohort of pediatric patients.

Analytic plan: Echocardiograms will be performed on the same day as the CMR, and will be performed by a group of sonographers trained in 3D volume acquisition. Descriptive statistics will include mean and median absolute % error and coefficients of variation. A paired t-test will be used to compare raw differences in %error for apical vs. subcostal window measurements. If the %error is highly skewed, a Wilcoxon signed-rank test will be used or the %error values will be log-transformed before application of the paired t-test (if no zero %error values exist). Linear regression will be used to estimate the window-differences in %error or log(%error) controlling for age and/or sedation status. Assessments of feasibility for both windows will be performed as described by Renella et al; and reproducibility of measurements made with echo vs. CMR will be also be graphically assessed using Bland-Altman plots of the raw measurements for data derived from each window. As a secondary (stratified) analysis, we anticipate dividing the cohort into 2 groups of 25 patients each (25 < 10y; 25 > 10y). Patients under 10y will typically be under anesthesia. Exploratory analyses will investigate subgroup differences defined by demographic/ surgical variables with respect to the magnitude of the difference between the 2 techniques. Of note the analyses performed above will also be performed for LV (in addition to RV) as a secondary analysis (with comparison of LV-specific vs. non-LV specific software, as appropriate).

Sample size/Power: funding is provided for 50 patients and this will be our target sample size. The analysis will be paired, to compare the %error (echo relative to MRI) measurements from apical vs. subcostal windows). To detect a 0.5 SD difference in apical vs. subcostal windows %error with 85% power, 38 subjects with echo & MRI are required. If the comparisons are performed stratified by age (25 subjects per age group), there is 80% power to detect a 0.58 SD difference in apical vs. subcostal windows %error.

Limitations: CMR, while considered a gold-standard, has a certain amount of intrinsic variability in volume measurement. Moreover, a statistically significant difference may not necessary be a clinically important difference. Patients will not have echo and CMR performed at the exact same time.