RESULTS
Population
One hundred and one children with structurally normal hearts were included in the LV analysis and 98 in the LA analysis. Of the subjects, 51 (51%) were female and 49 (49%) were male. The median and range for height was 127cm (57 – 195cm) and for weight was 25kg (5.2 – 139kg). Body surface areas between 0.5 and 1kg/m2 composed the greatest proportion of the group (42%) whereas BSA <0.5kg/m2 were less well represented (12%) (Table 1).
Assessment of regression
The end-diastolic and end-systolic measurements were first regressed against BSA and tested for heteroscedasticity. All measurements demonstrated a strong correlation with BSA. Both TT derived and VMS derived LV and LA EDV showed significant heteroscedasticity using the Breusch-Pagan F-statistic. Power transformation provided the best model for the relationship between BSA and all volumes, however, heteroscedasticity was accentuated. A log-log transformation of volumes and BSA eliminated heteroscedasticity with acceptable overall residuals (Table 2). Average, standard deviations and upper and lower normal ranges for values indexed using the optimal power transformation are shown in Table 3 and 4. Calculation of z-scores for study values using the best fit power regression revealed that 5 - 6% of diastolic and systolic study values using either technique fell beyond the 2 standard deviation range (Table 3).
Agreement and reliability
LA Volumes: There was very good to excellent correlations between VMS and Tomtec measuring LA systolic and diastolic volumes: LAESV ICC 0.94 (95% CI 0.90,0.96), LAEDV ICC 0.87 (95% CI 0.81, 0.91). On average Tomtec LA measurements were greater than VMS measurements with a small mean bias: LAESV (mean difference 6.6±1.9% (limits of agreement 44%, -31%), LAEDV (mean difference 6.5% (95% CI 47%, -60%). The Pearson correlation coefficient for LA ESV was 0.94 and for LA EDV was 0.87
LV Volumes: Tomtec derived ventricular measurements were higher than VMS measurements on average, with no difference in variability. The mean bias between Tomtec and VMS measurements of LVEDVi was 7.5ml±9.2ml or 15.5±1.9% (limits of agreement: 52.9%, -22.3%), and LVESV was 1.7ml±4.2ml or 7.3±2.0%, (limits of agreement 47.1, -32.5%) (Table 3, Figure 1). There was very good to excellent correlations between VMS and Tomtec measurements of LV systolic and diastolic volumes: LV systolic ICC 0.93 (95% CI 0.89, 0.95), LV diastolic ICC 0.92 (95% CI 0.79, 0.96). The Pearson correlation coefficient for LVEDV was 0.94, and for LVESV was 0.94. LV and LA linear regression scatter plots are displayed in Figure 2.
Efficiency :
VMS analysis time was shorter than Tomtec for both the LA and LV (Table 5). LV analysis time (total EDV and ESV) using TomTec vs VMS analysis time had an estimated difference of 0.75 minutes (95% CI 0.56, 0.94, p<0.0001) For LA analysis time, there was an estimated difference between TomTec and VMS of 1.23 minutes (95% CI 1.01,1.45, p<0.0001).
Reproducibility :
Interobserver Agreement (IOA): We used a two-way agreement model with 95% confidence interval to report IOA completed on 23 Tomtec analyses and 18 VMS analyses of the LV and LA. There was excellent IOA for Tomtec LAESV (ICC 0.96 (95% CI 0.90 – 0.98)), VMS LAESV (ICC 0.90 (95% CI 0.75 – 0.96)) and VMS LAEDV (ICC 0.92 (95% CI 0.64 – 0.98). There was good IOA for Tomtec LA EDV (ICC 0.84 (95% CI 0.13, 0.95), with several outliers accounting for wide confidence intervals. There was excellent IOA for TomTec LVEDV (ICC 0.95 (95% CI 0.56 – 0.98)), VMS LVEDV (ICC 0.97 (95% CI 0.90 – 0.98)) and VMS LVESV (ICC 0.96 (95% CI 0.90 – 0.99)) and good IOA for LVESV (ICC 0.77 (95% CI 0.53 – 0.89). LA & LV interobserver regression analysis and Bland-Altman plots of agreement are displayed on Figures 3 and 4 respectively.
Intra-observer agreement (IAOA): We used two-way agreement model with 95% confidence interval to report IAOA completed on 21 studies. There was excellent IAOA for VMS LAESV (ICC 0.99 (95% CI 0.95 – 1.0) and VMS LAEDV (ICC 0.96 (95% CI 0.76 – 0.99). There was also excellent IAOA agreement for TomTec LAESV ICC 0.96 (95% CI 0.91 – 0.98) and good agreement for LAEDV (ICC 0.86 (95% CI 0.52 – 0.95)). VMS and TT LA intra-observer regression analysis and LA Bland-Altman plots of agreement are displayed on Figure 5 and 6 respectively. TomTec LV intra-observer agreement was performed as part of a multicenter study13.