All patients enrolled in the study were subjected to the following:
Two-dimensional transthoracic echocardiogram
Full transthoracic echocardiogram using a Philips iE33 machine (Philips Medical Systems, Andover, MA). Standard 2D echocardiogram was done for all patients enrolled in the study using phased array transducers of different frequencies tailored according to each patient’s age, body built and weight.
The study included 2D, M-mode and color flow Doppler from all standard echocardiographic windows (i.e. sub costal, apical, parasternal and supra sternal) applying the sequential analysis to detect any associated congenital anomalies. Three views were used to visualize the inter-atrial septum, the sub costal biatrial view, the sub costal sagittal or bicaval view and parasternal short axis view. Two dimensional (2D) and color flow mapping were used to evaluate the site and diameter of the ASD in the 3 views [6]. The maximum diameter in any of the 3 views was recorded as the maximum transthoracic echocardiographic (TTE) diameter of the ASD.
Patients deemed suitable for ASD device closure were then subjected to the following:
Three-dimensional echocardiogram [6]
After completing the 2D echocardiography, all subjects underwent 3D echocardiogram study by an independent operator blinded to the data obtained by both TTE and 2D TEE. In patients, less than 20 kg body weight a 3D TTE data were obtained using the Vivid 9 GE machine 4V probe and for patients more than 20 kg 3D TEE data were obtained using the vivid 9 GE machine TEE 6VT probe.
We used the 3D zoom prepare modality for image acquisition. In 3D TEE, the bicaval view was acquired at the mid-esophageal level with the transducer starting at the 90 to 120 degrees. The depth of pyramidal data sets was adjusted to include only the left and right sides of the atrial septum in this view to allow the entire septum to be acquired in a 3D format without incorporating the surrounding structures. With a 90 degree up–down angulation of the pyramidal data set, the entire left-sided aspect of the septum could be shown in an “en face perspective”.
Once the left side of the atrial septum has been acquired, a rightward tilting of the volume will show the right side of the atrial septum and the fossa ovalis as a depression on the septum. In some cases, fine cropping using the arbitrary crop plane was necessary to remove the surrounding atrial structures obscuring the septum. A gain setting at medium level was required to avoid the disappearance of the fossa ovalis and creating a false impression of an ASD (Fig. 1).
For 3D TTE image acquisition, we used the 3D zoom prepare in the sub-coastal window, bicaval view then the volume was oriented to view the IAS from the RA with the SVC located at the 11-o’clock position (Fig. 2).
In terms of data analysis, after adjusting the sector aiming for the septum to be in the “en face view”, excluding possibility of oblique view, the defect area and circumference were measured by ball tracking the defect, the defect shape, position and 2 dimensions were documented in the 3D image.
Two dimensional transoesophogeal echocardiogram
2D TEE was done on the day of the procedure inside the cath. Lab. under general anesthesia.
Five key views were used to assess the IAS and surrounding structures these views include the upper esophageal short-axis view, mid esophageal aortic valve short-axis view, four-chamber view, bicaval view, and long-axis view.
Thorough evaluation of the rims surrounding the defect was done. A deficient rim was defined as less than 5 mm in at least three sequential related multi plane views in 15 degrees increments [6]. The presence of normal pulmonary venous drainage was confirmed and the presence of a fenestrated defect or other anatomical variants was also recorded.
The maximum ASD diameter defined as the largest diameter measured between 2 stable rims in any of the recorded views was used for further analysis.
Trans-catheter ASD closure
All procedures were done under general anesthesia. Right femoral vein access was established using Sildenger’s technique. After crossing the defect, multipurpose catheter was advanced into the upper left pulmonary vein and 0.35/260 stiff guidewire positioned in that vein. Balloon sizing of the defect was done in defects which were seen to have floppy rims by 2D TEE. The balloon stretched diameter was measured by both cine recording and TEE. The delivery sheath was then advanced over the wire. The device was then loaded and advanced to the tip of the sheath and deployed using standard technique. In some patients with difficult alignment of the device along the IAS; right upper pulmonary vein approach or balloon assisted technique was used.
Device measurements
Device size selection was 1-4 mm larger than the maximum diameter measured by TEE depending on the stability of the ASD rims and whether or not a balloon sizing was used. Due to the circular nature of the device waist, device area and device circumference were calculated as: device area = μr2 and device circumference = 2 μr respectively where the device radius (r) was calculated as device size/2.
Statistical analysis
All data were gathered, tabulated, and statistically analyzed on a PC using a commercially available statistical software package MedCalc version 11.6.1.0 (MedCalc Software, Mariakerke, Belgium). Qualitative variables were expressed as frequencies and their related percentage. Quantitative variables were expressed as mean ± SD. Independent sample T test was used to compare different quantitative variables. Pearson linear correlation was used to determine the correlation between three dimensional measurements and measurements obtained by two dimensional echocardiogram as well as device size, device area and device circumference. Regression analysis was used to generate two equations to predict optimal device size for ASD closure based on 3D derived ASD area and 3D derived ASD circumference. P-value was considered significant if <0.05, and P<0.01 was considered highly significant.