Materials & methods
Population :
Healthy pediatric patients aged 0-18 years referred for murmurs, syncope or chest pain with normal hearts identified by 2DE during their routine clinical evaluation were recruited for an additional research echocardiogram. Clinical data were taken from the medical records and included age, sex, weight, height, and medical history. Anyone with insufficient image quality precluding measurement using either software was excluded. The study was approved by the Institutional Ethics Review Board.
Real-Time Three-Dimensional Echocardiography :
The 3DE data sets were obtained using iE33 or Epic C7 machines (Philips, Andover, MA) with a matrix transducer X5 or X7. Apical 4 chamber view full volume acquisitions to include the entire LV were obtained. Full volume acquisitions were over 4-7 consecutive beats with no significant stitch artifact. The same process was completed for the LA.
3D volumetric data analysis :
Uncompressed 3D DICOM datasets focused on the LV or LA were imported into Tomtec Image Arena. LV and LA end systolic (ES) and end diastolic (ED) volumes and ejection fractions (EF) were measured using TomTec Image Arena 3D LV analysis package. A single cardiac cycle was defined using mitral valve (MV) closure. For the LV, the apex and aortic valve (AoV) were defined, and automated tracking was adjusted visually against the 2D imaging planes (four, three and two chamber apical views).
The same 3D DICOMs datasets were imported into VMS software, and reference points from recreated four, three and two chamber view imaging planes were manually placed at the AoV, MV, apex and LA and LV chamber walls as per the VMS protocol at both end systole and end diastole. The software generates a KBR-derived ESV and EDV and ejection fraction for each chamber (Figure 1).
The time taken to complete LA and LV volumetric analysis via TomTec and VMS were recorded.
Statistical Methods :
To adequately assess technique differences across a range of ages, sex and BSA with a power of 0.8 and alpha of 0.05, and assuming a standard deviation of 15% within techniques, 101 patients were included in this study.
The relationship between end-diastolic and end-systolic values with body surface area was assessed using linear regression modelling, with Breusch-Pagan testing for heteroscedasticity. Logarithmic transformation was used to reduce heteroskedasticity where present, and optimal regression with BSA was identified using curve-fitting.
Analysis time between Tomtec and VMS was compared using a non-paired Student’s t-test. Linear regression models were used to compare the two software measurements of LV and LA ES and ED volumes and EF. Intraclass coefficients (ICC) were calculated, and Bland-Altman plots constructed for comparison of the two software algorithms. For interobserver agreement (IOA) and intra-observer agreement (IAOA), we randomly selected subjects for reanalysis by two of the investigators, LE & AA (IOA – LE, IAOA AA), and a two-way agreement model with 95% confidence interval and constructed Bland-Altman plots were used. All statistical analysis was performed using StataIC 14 (College Station, Texas).