Discussion:
In this study, 3D TEE and 2D maximal ASD diameters were found to be correlated with the device size. 3D Echocardiography has a good ability to overcome geometric assumptions and the variability in the ASD measurements.
3D Echocardiography is now widely available and validated protocols for accurate measurement of different cardiac defects are now established.
Balloon sizing is the widely used and approved technique till the moment. However, it is thought to overestimate the defect size due outstretching the defect margins. At the meantime it adds an extra cost to the procedure besides the prolonged exposure to fluoroscopy.(Zhu et al., 2000)
Underestimation of the defect size could lead to serious complications for example device dislodgment. Meanwhile, overestimation of the defect size is not appropriate too. The routine use of a bigger device has a safety concerns as it could lead to encroachment on the surrounding structures. It may result in serious complications like heart block and aortic erosion.(Zhu et al., 2000)
The main result of this study is the good correlation between the maximal ASD measurement assessed by 3D-TEE and the device size. We assumed that the device size was accurate in cases where there was no residual leak , encroachment on surrounding structures or any major complications e.g., device dislodgement. We correlated the device size with the different Echocardiographic maximal diameters.
The correlation between the device size and the Echocardiographic maximal diameters was higher with 3D TEE than other maximal diameters. R2 0.72, P ≤0.001
With multiple linear regression analysis, we suggest a formula that can predict the device size according to the 3D TEE maximal diameter: Device size = 6.9 + 0.87 x 3D maximal diameter with R2 = 0.72, P ≤0.001 .We can use 2D TEE maximal diameters but this could have a lower predictive value than the 3D measurement: Device size =8.9 +0.87 x 2D TEE maximal diameters R2=0.69, P ≤0.001, However, all these formulas needs to be validated on a larger number of patients.
Hajizeinali et al compared the 2D TEE maximal diameter with the device size and suggested a formula to predict the device size using the 2D maximal diameter. They proposed the following equations to calculate a device size:
Device size = 2.76 + 1.16 × TEE defect size, R2 = 0.91
Device size = 4.08 + 1.05 × TEE defect size, R2 = 0.91 (Hajizeinali et al., 2013)
There is some difference between this result and our results. We attribute this to the difference in sample size, and some technical aspects; for example, the variability in selecting the device size to be 1-4 mm larger than the defect size.
Hascoet et al suggested that 3D TEE maximal diameter was correlated to the balloon size. They suggested two formulas BS = 1.07 × 3D TEE max- 0.1 when the ASD shape was oval and BS =1.07 × 3D TEE max+3 when the ASD shape was round. (P, 0.0001). R2 was 0.78. (Hascoet et al., 2015)
We thought that correlating the 3D maximal diameter directly to the device size would have an added benefit if the 3D proved efficacy in accurately assessing the defect size. It reduces the time of the procedure and minimize radiation exposure and more importantly decreases the cost.
Another model which was described by (Hascoet et al., 2015) is BS = 4.5 × ASD area+11.5 (P , 0.0001). R2 was 0.74.
Roushdy et al. suggested a formula which used the 3D area and circumference to predict the device size (Roushdy et al., 2020) . The suggested formulas were:
a-Device size = 10.8 + 3.95 x 3D ASD area.
b-Device size = 3.85 x 3D ASD circumference −1.02.
However, we used the 3D maximal diameter as it is the previously known practice and it is easier to apply.
Based upon our results we suggest that 3D TEE can be used solely to choose the suitable device without the need for balloon sizing .This will reduce the duration of the procedure, minimize the radiation exposure, avoid the defect margins distortion that is probable with the overstretched balloon and more importantly reduces the cost of the procedure. However, this needs to be validated by a larger study.