Background
The effect of the atrial septal defect (ASD) shape on ASD size measurements remains unclear. We assessed the relationships between the stretched balloon diameter (SBD) and the diameters measured using two-dimensional and three-dimensional (3D) transesophageal echocardiography (TEE) and evaluated the effect of ASD shape on these relationships in patients with secundum ASD.
Methods
We prospectively enrolled 107 consecutive patients who underwent transcatheter closure of ASD. The SBDs and ASD diameters on two-dimensional and 3D-TEE were measured. The circular index of the ASD was defined as the ratio of the maximal diameter to the minimal diameter on the 3D-TEE image. All patients were clinically followed up for a median of 1.3 months after the procedure.
Results
The correlations and agreements between measurements were significantly better in patients with a round (circular index less than 1.5) than with an oval ASD. The differences between the SBDs and maximal diameter on 3D-TEE images were significantly smaller in patients with a large oval ASD than in the other patients. The differences between the size of the devices finally implanted and maximal diameter on 3D-TEE images were smaller in patients with a large oval than with a round ASD. On multivariate linear regression analysis, a formula of the relationship between the finally selected device size and 3D-TEE parameters was constructed: device size = 0.964 × maximal diameter on 3D-TEE image − 2.622 × circular index + 7.084. No major complications, including device embolization, developed during follow-up.
Conclusions
The relationships between the SBDs and maximal diameters measured on two-dimensional and 3D-TEE images are influenced by the ASD shape and size. Therefore, the ASD shape, as well as the size, should be considered when the device size is determined without SBD measurement.
Transcatheter closure of secundum atrial septal defects (ASDs) has become an alternative approach to surgery in selected patients and has demonstrated good intermediate- and long-term clinical outcomes. However, device embolization is a rare, but serious, complication requiring emergency surgery. It can occur when the device size is too small for the ASD, and an oversize device can increase the risk of erosion, especially in patients with a deficient aortic and/or superior rim. Therefore, the determination of the device size is one of the critical steps in this percutaneous procedure.
The standard method of determining the device size is measurement of the stretched balloon diameter (SBD). The balloon, however, can overstretch the ASD, overestimating the ASD size in some patients. Moreover, the relationship between the SBD and the maximal ASD diameter, as measured by two-dimensional (2D)-transesophageal echocardiography (TEE) is not uniform. The maximal ASD diameter without measurement of the SBD is frequently used to determine the device size needed to avoid overestimation and eliminate cumbersome balloon sizing procedures. The relationship between the SBD and maximal ASD diameter can also be affected by the shape of the ASD (i.e., round or oval), but this has not been well evaluated.
Three-dimensional (3D)-TEE is a superior imaging method that can assess the number, shape, and surrounding structures of an ASD in a single view. Using an en face view, the entire ASD shape can be evaluated visually, and its maximal diameter can be measured. However, the relationships between the diameters measured on 3D-TEE images and other parameters, such as the SBDs and the diameters measured on 2D-TEE images, remain to be determined, especially in relationship to the ASD shapes. We, therefore, assessed the relationships between SBDs and diameters measured on 2D- and 3D-TEE images in patients with secundum ASD. We also evaluated the effect of ASD shape on these relationships.
Methods
Patients and Protocols
We prospectively enrolled 107 consecutive patients (mean age 44.9 ± 13.7 years, 78 women) who underwent closure of a single ASD using the Amplatzer septal occluder (AGA Medical, Golden Valley, MN) from November 2009 to August 2011 in the Asan Medical Center. The institutional review board approved the present study and waived the requirement for individual informed consent because all images were acquired during routine clinical practice and the research involved no more than minimal risk to the subjects.
All procedures were performed with the patients under general anesthesia with TEE guidance, and 2D- and 3D-TEE images were acquired for all patients. After femoral venous puncture, we measured the SBD of the ASD using the Amplatzer sizing balloon II (AGA Medical). A bolus of 100 IU/kg heparin was infused at the beginning of the procedure. The size of the Amplatzer septal occluder (AGA Medical) was determined by taking all measurements, including the sizes measured from TEE, SBD, and ASD shape on the 3D-TEE images, into account. Immediately after the procedure, 2D-TEE, including color Doppler images, was performed to determine whether any device malposition, embolization, or significant remnant shunt was present. Patients were prescribed 100 mg/day or more of aspirin at least for 6 months after the procedure. All patients were clinically followed up for a median 1.3 months (range 0.03–13.5).
Echocardiographic Analyses
We performed 2D- and 3D-TEE using an iE33 ultrasound machine and a 3D matrix array 2–7-MHz TEE probe (Philips Medical Systems, Andover, MA) during the procedure with the patients under general anesthesia. The ASD diameters on 2D-TEE were measured on more than four views at various angles (0°–180°), including short-axis images at 30°–60° and long-axis images at 90°–100° ( Figure 1 A). After evaluating an en face view of the ASD using 3D-TEE and identifying the angle at which the ASD diameter was maximal, we used this angle to measure the diameter on 2D-TEE. The ASD diameters were measured on the end-systolic frame of the cardiac cycle, when the sizes appeared largest. We determined the maximal and minimal diameters for all the diameters measured.
The 3D full-volume images were acquired during patient breath-hold, when the anesthesiologist temporarily stopped the respirator. Care was taken to include the whole ASD in a full-volume image, and the images were obtained after the gain, compression controls, and time gain compensation settings were optimized to ensure image quality. The ASD shapes were evaluated on en face views from the left atrial side. All images were stored digitally and analyzed off-line using dedicated software (TomTec GmbH, Munich, Germany). All measurements of 3D-TEE images were independently conducted without knowing the 2D and SBD results. On the multiplanar reconstruction images, the longitudinal planes of the maximal and minimal ASD dimensions were identified using guidance on the en face image of the ASD ( Figure 1 B), and the diameters were measured on the longitudinal planes. The diameters were measured on the end-systolic frame when the ASD size appeared largest. The circular index of the ASD was defined as the ratio of its maximal to minimal diameters on 3D-TEE image. The patients were classified using the circular index, with the round (RD) group defined as those patients with a circular ASD shape (circular index less than 1.5) and the oval (OV) group defined as those with an oval ASD (circular index 1.5 or greater). The patients in each group were divided into two subgroups according to their maximal ASD diameters measured on 3D-TEE images. Patients in the RD and OV groups with a maximal diameter of less than 20 mm were classified into the RD, small and OV, small subgroups, respectively. Those with maximal diameters of 20 mm or greater were classified into the RD, large and OV, large subgroups ( Figure 2 ). The 3D-TEE images of 20 randomly selected patients were used for evaluation of the intra- and interobserver variabilities of the maximal and minimal ASD diameters.
Stretched Balloon Diameters
The sizing balloon was gradually inflated with diluted contrast agent until no shunt flow was observed on the color Doppler TEE image. TEE guidance was used throughout the sizing procedure to ensure proper positioning of the balloon catheter at the ASD. Fluoroscopic recordings were taken from the anteroposterior projection, and the SBD was measured directly using quantification software immediately after the balloon sizing procedure ( Figure 1 C). The SBD was also measured using 2D-TEE ( Figure 1 D).
Statistical Analysis
The data are expressed as the mean ± SD. Statistical analyses were performed using SPSS (SPSS, Chicago, IL). Comparisons between measurements were performed using paired t tests, linear regression analysis, and calculation of the mean difference. The strengths of the correlations were compared using Fisher’s Z-transformation. Bland-Altman analysis was used to evaluate the agreement of two parameters. The mean values in the four subgroups were compared using one-way analysis of variance and post hoc analyses. Multivariate linear regression analysis was used to construct an equation to identify optimal device size using the 3D-TEE measurements. Intraobserver variability was determined by the same observer at two separate sittings more than 12 weeks apart in 20 random 3D-TEE images. The second round of intraobserver measures was unaware of the results from the initial measures. Interobserver variability was assessed by 2 blinded observers, who independently selected the end-systolic frames and measured the diameters in 20 random 3D-TEE images. The inter- and intraobserver variabilities were evaluated using the intraclass correlation coefficient and the coefficient of variation. P < .05 was considered statistically significant.
Results
The measurements of the ASD size and device size used for transcatheter occlusion of ASD in the study population are listed in Table 1 . The ASD diameters measured from the short-axis view of the 2D-TEE images (16.1 ± 6.3 mm) were significantly larger than the minimal diameters (13.8 ± 4.9 mm, P < .001) and significantly smaller than the maximal diameters (18.5 ± 5.9 mm, P < .001) measured using 2D-TEE. The ASD diameters measured on the long-axis 2D-TEE view (15.2 ± 5.0 mm) were also significantly larger than the minimal diameters ( P < .001) and smaller than the maximal diameters ( P < .001) measured using 2D-TEE. The maximal ( r = 0.954, P < .001) and minimal ( r = 0.906, P < .001) diameters measured using 3D-TEE showed excellent correlations with those using 2D-TEE ( Figure 3 ). The maximal (18.5 ± 5.9 mm vs 17.9 ± 5.9 mm, P = .003) and minimal diameters (13.8 ± 4.9 mm vs 13.0 ± 4.8 mm, P < .001) measured using 2D-TEE were significantly larger than those measured using 3D-TEE, although the mean differences were quite small.
| Variable | Mean ± SD (mm) |
|---|---|
| 2D-TEE | |
| Short-axis view | 16.1 ± 6.3 |
| Long-axis view | 15.2 ± 5.0 |
| Maximal diameter | 18.5 ± 5.9 |
| Minimal diameter | 13.8 ± 4.9 |
| 3D-TEE | |
| Maximal diameter | 17.9 ± 5.9 |
| Minimal diameter | 13.0 ± 4.8 |
| SBD | |
| 2D-TEE | 18.8 ± 5.9 |
| Fluoroscopy | 19.6 ± 5.6 |
| Device size | 20.6 ± 6.0 |
We observed an excellent correlation between the SBDs measured using 2D-TEE and fluoroscopy ( r = 0.926, P < .001; Figure 4 ). However, the SBDs using 2D-TEE were significantly smaller than the SBDs with fluoroscopy (18.8 ± 5.9 vs 19.6 ± 5.6 mm, P < .001). The maximal diameters measured with 3D-TEE showed an excellent correlation with the SBDs measured using fluoroscopy ( r = 0.899, P < .001, Figure 5 ), although, in general, the maximal diameters on 3D-TEE were significantly smaller than the SBDs using fluoroscopy, with a mean difference of 1.6 ± 2.6 mm ( P < .001). Similarly, the maximal diameters on 2D-TEE showed an excellent correlation with the SBDs measured using fluoroscopy ( r = 0.914, P < .001), but the maximal diameters with 2D-TEE were also smaller than the SBDs using fluoroscopy, with a mean difference of 1.1 ± 2.4 mm ( P < .001).
The mean circular index was 1.43 ± 0.30 (range 1.0–2.67). The correlations between the maximal ( r = 0.974 vs r = 0.931, P = .007) and minimal ( r = 0.933 vs r = 0.849, P = .018) diameters using 2D- and 3D-TEE were greater in the RD than in the OV group ( Figure 6 ). Similarly, the correlation between the maximal diameters measured using 3D-TEE and SBDs using fluoroscopy was stronger in the RD than in the OV group ( r = 0.946 vs r = 0.822, P = .001), as was the correlation between the maximal diameters measured using 2D-TEE and SBDs using fluoroscopy ( r = 0.949 vs r = 0.857, P = .004). The limits of agreement between the measurements were narrower in RD group than in the OV group using Bland-Altman analyses.
When the patients were classified into the four subgroups according to the shape and size of the ASD, we found that the differences in the maximal diameters measured using 3D- and 2D-TEE differed significantly among the four groups ( P = .006), with post hoc analyses showing that these differences were significantly greater for the OV, large group than for the RD, small and RD, large subgroups ( Table 2 and Figure 7 ). We also found that the differences between the SBDs measured fluoroscopically and the maximal diameters measured using 3D-TEE differed significantly among the four subgroups ( P = .002), with significantly smaller differences in the OV, large subgroup than in the other three.
| Variable | RDsm (n = 38) | RDlg (n = 27) | OVsm (n = 26) | OVlg (n = 16) | P value |
|---|---|---|---|---|---|
| 3D max vs 2D max | −0.9 ± 1.2 ∗ | −1.0 ± 1.5 ∗ | −0.2 ± 2.0 | 0.6 ± 2.5 | .006 |
| SBD fluoro vs 3D max | 2.0 ± 1.7 ∗ | 1.6 ± 2.2 ∗ | 2.4 ± 2.8 ∗ | −0.5 ± 3.5 | .002 |
| Device vs SBD fluoro | 1.1 ± 1.6 † | 1.9 ± 2.0 † | −0.2 ± 1.8 ∗ | 1.5 ± 2.5 | .001 |
| Device vs 3D max | 3.1 ± 1.7 ∗ | 3.5 ± 1.6 ∗ | 2.2 ± 2.2 | 1.1 ± 2.3 | < .001 |
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