Background
Successful transcatheter closure of atrial septal defects (ASDs) requires the accurate assessment of defect size and morphology. Assessment of ASD anatomy may be difficult by two-dimensional (2D) echocardiography. The aim of this study was to test the hypothesis that real-time three-dimensional (3D) transesophageal echocardiography (TEE) may provide more accurate morphologic assessment of ASDs than multiplane 2D TEE.
Methods
Twenty-four patients with ASDs were imaged using 2D and real-time 3D TEE. ASD shape and size were assessed using 3D TEE retrospectively. Maximal ASD dimensions obtained by 3D TEE were compared with unstretched and balloon-stretched dimensions on 2D TEE. Planimetered defect area by 3D TEE was compared with area calculated using the ellipse formula from 2D imaging. Twenty of the 24 patients underwent transcatheter ASD closure. Closure device size was based on findings on 2D TEE. Follow-up was conducted by 2D transthoracic echocardiography.
Results
Of the 24 ASDs, 6 (25%) were circular, 10 (42%) were oval, and 8 (33%) were complex in shape. The mean maximal dimension was larger by 3D TEE compared with 2D TEE (1.8 ± 0.8 vs 1.5 ± 0.6 cm; P < .05). There was no difference in the mean area measured by either modality, but for complex-shaped defects, area measured by 3D TEE was larger than that by 2D TEE (2.8 ± 1.3 vs 1.7 ± 1.4 cm 2 ; P < .05). Follow-up transthoracic echocardiography was available for 19 of the 20 patients undergoing transcatheter closure. Nine patients had residual right-to-left shunting 1 to 6 months after ASD closure, and the majority of these were complex in shape. In patients with residual shunting, ASD area by 3D TEE was 27% larger than by 2D TEE, whereas in patients without residual shunting, there was significantly less discrepancy between 3D and 2D areas (19%; P = .0027).
Conclusions
Three-dimensional TEE can identify ASD shape. Maximal dimensions on 3D TEE were well correlated with balloon-stretched 2D dimensions. Two-dimensional TEE can underestimate the area of complex-shaped ASDs, which may result in residual right-to-left shunting.
Atrial septal defects (ASDs) are the second most common congenital heart malformations encountered in adults. There are various types of ASDs, classified according to anatomy and location. Defects within the oval fossa are known as secundum defects and are the most common (60%) type of ASD, occurring most frequently in female patients.
Transcatheter device closure is a well-established, ever-increasing procedure used to treat patients with secundum ASDs. However, not all defects are anatomically suitable for transcatheter closure, as a sufficient rim of interatrial septal tissue between the defect and adjacent structures is required to seat the device. Thus, before the selection of a closure device, a detailed anatomic study is necessary to determine defect size, morphology, and the spatial relationship of the defect with its surrounding structures, such as the atrioventricular valves, the aortic valve, and the entry of the systemic and pulmonary veins.
Multiplane two-dimensional (2D) transesophageal echocardiography (TEE) is commonly used in the catheterization lab to guide transcatheter device implantation. However, despite its value in elucidating ASD morphology, challenges remain. Pathologic studies have shown that ASDs come in various shapes and sizes and in fact may be oval, circular, or more complex in shape. With standard multiplanar TEE, the dimensions of a defect can be measured only in multiple 2D planes, from which the defect size is estimated and the shape inferred. If the selected 2D planes do not reflect the true major or minor axis of the defect, then overestimation or underestimation of its size may occur.
Recent studies have indicated the potential for real-time three-dimensional (3D) TEE to guide ASD closure in selected patients. We report our experience of using real-time 3D TEE in a population of patients referred for transcatheter ASD closure at the Massachusetts General Hospital. Our findings are supported by an outcome analysis of patients over the 6 months following device closure.
Methods
Study Population
Twenty-six patients with secundum ASDs referred for transcatheter device closure over an 18-month period were enrolled and underwent comprehensive multiplane 2D and real-time 3D TEE. Three-dimensional transesophageal echocardiographic this can be shortened to TEE throughout the document data sets were analyzed retrospectively using offline software. Two patients had technically inadequate imaging for analysis and were excluded.
Criteria for the assessment of transcatheter device closure included a minimal circumferential rim of 4 mm of septal tissue around the defect to allow for the stable seating of the closure device and to provide adequate separation of the device from other important structures.
TEE
A matrix-array 3D transesophageal echocardiographic probe (X7-2t; Philips Medical Systems, Andover, MA) was used to acquire comprehensive multiplane 2D, Doppler, and real-time 3D imaging of the ASDs. Real-time 3D imaging of the defects included both 3D zoom and full-volume views. Analysis was performed using the best-quality images with the most complete anatomic views of the defects. Unstretched maximal diameters of the ASDs were measured using 2D and 3D TEE. The distances between the defect edges and surrounding anatomic structures were measured as follows: anterosuperior rim (distance from edge of defect to aorta), anteroinferior rim (distance from defect to tricuspid valve annulus), posterosuperior rim (distance to superior vena cava), and posteroinferior rim (distance to inferior vena cava). Balloon sizing was conducted at the discretion of the interventional cardiologist. When performed, the balloon was inflated until the disappearance of shunt flow by color Doppler across the defect, and then the diameter of the balloon was measured using 2D TEE.
Measurements used for device sizing and guidance of transcatheter closure were performed with standard multiplane 2D imaging. The 3D images were acquired but not analyzed until after the completion of the procedure. The transesophageal echocardiographic procedures were performed by staff echocardiographers in the Cardiac Ultrasound Laboratory at Massachusetts General Hospital, all of whom have achieved level III training in echocardiography and are highly experienced in the performance of TEE and in its use for guidance of various transcatheter procedures.
Analysis of 3D Echocardiographic Data
From each study, the 3D images providing the most complete anatomic information and best spatial resolution were selected for further analysis retrospectively. The acquired data set was cropped, and using the software tools, multiple 2D planes in various directions were constructed from the 3D data set (multiplanar reconstructions) (QLAB; Philips Medical Systems). A horizontal plane parallel to the plane of the atrial septum allowed for the display of the ASD en face from the left atrium. Simultaneously, two planes orthogonal to the horizontal axis of the atrial septum (bicaval or anterior-posterior views) were used to ensure that the horizontal/en face plane cut through the actual edges of the defect and ensured that this en face plane was parallel to the angle of the defect ( Figure 1 A).
En face views of the defects were constructed in this manner in at least three points of the cardiac cycle. All measurements from the en face view were obtained during the largest defect aperture (end-systole). The maximum long-axis dimension (length), minor-axis dimension (width), and area by planimetry were measured from the 3D en face view ( Figure 1 B). ASD area by 2D imaging was calculated from the ellipse formula using the measured length and width.
ASD morphology was further categorized by the shape seen in the en face view. We defined elliptically shaped ASDs as circular (or near circular) when the minor dimension was ≥75% of the maximum length. Elliptically shaped defects in which the minor dimension was <75% of the maximum length were defined as having an oval shape. Asymmetric, irregularly shaped defects that were not elliptical were defined as having a complex shape. Examples of complex-shaped defects included crescentic, sail-shaped, and teardrop-shaped defects ( Figure 2 A). The size of a defect did not bear upon whether it was classified as complex or not. For the purposes of this study, initial classification of all defects was according to shape only.
Transcatheter Device Closure
Right-heart and left-heart catheterizations were performed before ASD closure. The ratio of pulmonary to systemic blood flow (Qp/Qs) was calculated using the mixed venous, pulmonary artery, and femoral artery saturation. Balloon sizing was conducted at the discretion of the interventional cardiologist. Transcatheter ASD closure was performed using fluoroscopic and transesophageal echocardiographic guidance. Device selection was based on 2D transesophageal echocardiographic measures whether balloon sizing was used or not. When a defect was balloon sized, the diameter measured on 2D TEE was used for device selection. Final device size selection accounted for competing anatomic factors, requiring careful judgment particular to each case: the device had to be large enough to cover the entire ASD and to adequately engage the rims of the defect but small enough to avoid impinging on important adjacent structures and/or increase the risk for erosion.
Transthoracic echocardiography was typically performed 1 day following closure, before hospital discharge. Follow-up TTE with agitated saline contrast performed between 1 and 6 months after ASD closure was analyzed for evidence of residual shunting. Shunting was considered to be present when there was unequivocal passage of contrast across the device, to avoid confusion with the presence of intrapulmonary shunts. The interpreter was blinded to the defect measurements obtained by either the 2D or 3D TEE methods. All patients undergoing transcatheter device closure received an Amplatzer Septal Occluder device, except for 1 patient who received an Amplatzer Multi-Fenestrated Septal Occluder device (AGA Medical Corporation, Plymouth, MN).
Statistical Analysis
Data are expressed as mean ± SD. ASD maximal dimensions and area were compared using 2D and 3D imaging. Student’s t tests were used to compare continuous variables using a two-tailed P value < .05 for statistical significance. Pearson’s product-moment correlation coefficient was used to estimate the correlation between ASD area and Qp/Qs and to estimate the linear correlation between balloon-stretched diameters and maximal dimensions by either 2D or 3D imaging.
Results
Study Population
The baseline characteristics of the 24 study patients are shown in Table 1 . Eighteen of the 24 patients were women. The mean age was 48 ± 16 years (range, 17–82 years). Invasive hemodynamic assessment of shunting using Qp/Qs was available in 18 patients. The mean Qp/Qs in these patients at the time of catheterization was 2.0 ± 1.2. The primary indication for ASD closure was stroke or transient ischemic attack from presumed paradoxical emboli in six patients (25%); right ventricular dilatation with pulmonary hypertension, symptoms, or the presence of a significant shunt in 14 patients (58%); and symptoms in the absence of right ventricular dilation in four patients (17%). Symptoms included decreased exercise tolerance, dyspnea on exertion, presyncope, and/or atrial arrhythmias. All defects were secundum ASDs, and no patient had a patent foramen ovale detected.
| Clinical parameter | Value |
|---|---|
| Age (y) | 48 ± 16 |
| Men | 6 |
| Women | 18 |
| Qp/Qs ( n = 18) | 2.0 ± 1.2 |
| Primary indication for closure | |
| Stroke/TIA | 6 |
| RV dilatation ∗ | |
| With pulmonary hypertension | 7 |
| With symptoms ‡ | 3 |
| With a significant shunt † | 4 |
| Symptoms without RV dilatation | 4 |
∗ Echocardiographic indicators of RV dilatation or pulmonary hypertension in the context of a significant left-to-right shunt.
† A significant shunt was defined as Qp/Qs >2.0.
‡ Symptoms included decreased exercise tolerance, dyspnea on exertion, palpitation, and presyncope or syncope.
The acquisition of 3D images did not significantly extend intraprocedural TEE time. An additional time of up to 20 minutes was necessary for offline analysis of each 3D acquisition.
ASD Shape
Of the 24 ASDs, only six (25%) were circular ( Figure 1 A). Ten defects (42%) were oval ( Figure 1 B), and eight (33%) were complex in shape ( Figures 2 A and 2 B). Figures 2 B and 3 illustrate how the corresponding 2D transesophageal echocardiographic images acquired failed to depict the true maximum dimension of the defect.
ASD Size
The mean maximal dimension measured using 3D TEE was significantly larger than the 2D measurement ( Table 2 ). The width or minor-axis dimension was similar by either modality. The mean areas were 1.7 ± 1.3 cm calculated by the ellipse formula (by 2D imaging) and 2.0 ± 1.4 cm measured by planimetry from the en face view (by 3D imaging). Although not statistically significant in the overall group, the discrepancy between 2D and 3D assessments of defect area was related to the defect size. For defects with areas >2 cm 2 by planimetry, the mean area was significantly larger measured by 3D TEE than by 2D TEE (3.5 ± 0.9 vs 2.9 ± 1.2 cm 2 ; P < .05; Table 3 ). In contrast, there was no difference in the mean area for smaller defects (area ≤ 2 cm 2 ) as measured by 3D TEE compared with 2D imaging.
