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Original article

Reliability of transthoracic echocardiography in estimating the size of Amplatzer septal occluder and guiding percutaneous closure of atrial septal defects

LI, Gui-shuang; KONG, Guang-ming; JI, Qiu-shang; LI, Ji-fu; CHEN, Yu-guo; YOU, Bei-an; ZHANG, Yun

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Abstract

Interventional therapy for atrial septal defect (ASD) is progressing daily.1–6 Before intervention, accurate detection and measurement of ASD position, diameter and relation with neighboring structures by use of echocardiography is important to determine whether the ASD can be occluded and for the selection of the atrial septal occluder size.7–9 Pre-intervention examinations mainly include transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE). TEE and intracardic echocardiography (ICE) are excellent and standard imaging tools for guiding ASD transcatheter closure.10–16 In China, TTE is popularly used for pre-intervention examination for ASD and for guiding ASD closure. Results of pre-intervention examination are used as the basis for selecting the Amplatzer septal occluder size. However, the ability to determine size and the safety and efficacy of TTE for guiding ASD closure still has not been widely accepted. In this study, we investigated the practicality of the use of TTE for determining the ASD diameter for selecting the size of Amplatzer sepal occluder (ASO) needed and the safety and efficacy of TTE for guiding ASD closure.

METHODS

Patients

From January 2004 to June 2005, we enrolled 68 consecutive patients (15 men) with known ASD undergoing intervention for ASD in our hospital. The mean age was (33.7±17.3) years (range 4–67 years). The patients were divided into 3 groups according to their TTE-determined ASD diameter: 4–14 mm (group A, 22 patients); 15–20 mm (group B, 21 patients); ≥21 mm (range 21–33 mm) (group C, 25 patients).

Color ultrasound system

We used an Agilent SONOS 5500 ultrasound system (Agilent Technologies, Andover, MA, USA) and a 2.0–4.0 MHz S4 transducer for examination.

Transthoracic echocardiography examination

Before interventional therapy, all patients underwent TTE for measurement of atrial diameter and ventricles, observation of ASD diameter and relation between ASD and surrounding structures (Figures 1–4). Pulmonary artery systolic or mean pressure was estimated for patients with tricuspid or pulmonary valve regurgitation. Views were as follows: short-axis view to measure the ASD rims of ascending aorta side and posterior-inferior side; four-chamber view to measure the distance between the ASD and mitral annulus and atrium top; and subcostal view to measure the distance between the ASD and mitral annulus, the entrances of the superior vena cava and the inferior vena cava, to the total length of atrial septum. The largest ASD diameter measured in different views was selected as the reference ASD diameter (x). Patients were selected for ASD transcatheter closure following the Guideline of Catheter Interventional Therapy for Congenital Heart Diseases.17

Figure 1.
Figure 1.:
TTE in four-chamber view without (1A) and (1B) with color Doppler to demonstrate ASD, ASD diameter, the distance between ASD and mitral annulus and atrium top. RV: right ventricle; LV: left ventricle; RA: right atrium; LA: left atrium.
Figure 2.
Figure 2.:
TTE in short-axis view without (2A) and with (2B) color Doppler to demonstrate the ASD, ASD diameter, ASD rims at ascending aorta side and posteriorinferior side. AO: ascending aorta.
Figure 3.
Figure 3.:
TTE in subcostal view to demonstrate the ASD and superior vena cava, the ASD diameter, distances between ASD and mitral annulus and the entrances of the superior vena cava.
Figure 4.
Figure 4.:
TTE in subcostal view without (4A) and with (4B) color Doppler to demonstrate the ASD, IVC, and ASD diameter, distances between ASD and inferior vena cava. IVC: inferior vena cava.

Interventional therapy and occluder device

Adults and children (≥10 years) underwent local anaesthesia, and children younger than 10 years underwent general anaesthesia. TTE was used as the image guiding tool during the procedure. An ASO (AGA Medical Corp., Golden Valley, MN, USA) was used for ASD closure. Heparin was always given to maintain activated clotting time above 200 seconds. For groups A, B and C, ASO size was, on average, 3, 5 and 8 mm, respectively, larger than the ASD measured by TTE. For each patient, ASO selection involved the following factors as well: ASD position, whether the ASD rim was intact, and whether the rim was soft or stiff. If the ASD was located at the centre of the atrial septum and the rim was intact and stiff, a relatively smaller ASO was selected; otherwise, a relative larger ASO was selected. The ASO left disc was generally opened in the left atrium; if a large ASO could not be fixed, we tried to open the left disc in the left-superior pulmonary vein or in the right-superior pulmonary vein. All patients received aspirin for 1 to 3 days before and until 6 months after surgery.

Follow-up

Immediately after surgery, one day after and 1, 3, and 6 months after surgery, all patients underwent TTE to determine ASO malposition, residual shunt or thrombus on the surface of the ASO. Diameters of cardiac chambers and pulmonary artery pressure were also measured for some patients.

Statistical analysis

Data were analyzed with use of SPSS 13.0 (SPSS, Chicago, IL, USA). Quantitative variables were compared by repeated measures analysis of variance (ANOVA). Data are presented as mean ± standard deviation (SD). A two-tailed P <0.05 was considered statistically significant. Linear regression equations were established between ASO size (y) and ASD (x). 95% confidence intervals (CI) and correlation coefficients were reported.

RESULTS

Every ASD in groups A and B was successfully occluded with one ASO, with no complications or residual shunts. The left disc was opened in the left atrium in all patients.

In group C, occlusion failed in 2 cases, and the ASO was pulled out. In 4 cases, the ASO was too small to be fixed, and a larger ASO was used and successfully deployed. The ASO was released 1.8 times, on average, in successful cases. In one case, release of ASO was attempted 10 times. The left disc was opened in the left-superior pulmonary vein in one case, and opened in the right-superior pulmonary vein in 2 cases. In one case, after releasing the ASO, a 3-mm residual shunt was detected and remained until 6-month follow-up. In another case, thrombosis appeared on the surface of the ASO on the second day and disappeared 7 days after intensive anticoagulative therapy, including heparin infusion and warfarin oral administration.

A total of 18 ASDs had no rims at the ascending aorta side, but all of these ASDs were successfully closed without complications.

No thromboembolism, ASO dislocation or death occurred during 6-month follow-up.

Relation between ASD diameter (x) measured by TTE and size (y) of ASO used successfully to occlude the ASD

The diameter of ASD measured by TTE could accurately predict the ASO size that could successfully occlude the ASD, especially in patients with ASD <20 mm. The ASD diameter measured by TTE correlated well with ASO size. The diameters for the ASD and ASO are as follows for the three groups: Group A: ASD (x), (9.68±2.83) mm, ASO (y), (12.77±3.96) mm (range 6–20 mm), y-x= (3.09±2.04) (range 0–6 mm, 95%CI: 2.18–3.99; compared with group B: P=0.022; compared with group C: P<0.001), regression equation: y=1.22x+0.99 (r=0.925, P <0.001). Group B: ASD, (17.14±1.53) mm, ASO, (22.5±2.84) mm (range 18–28 mm), y-x=(4.90±2.36) mm (range 2–7 mm, 95% CI 3.83–5.98, compared with group C: P=0.001), regression equation: y=1.03x+4.43 (r=0.976, P <0.001). Group C: ASD, (26.87±2.75) mm, ASO, (34.52±4.23) mm (range 26–40 mm), y-x=(7.65±3.05) mm (range 5–13 mm, 95% CI 6.33–8.97), regression equation: y=1.07x+5.89 (r=0.929, P <0.001). The larger the ASD, the much larger the ASO needed and the more difficult the procedure.

DISCUSSION

The position, shape and diameter of ASD are key factors for deciding whether an ASD can be occluded through a catheter, what ASO size is required and the possibility of success. The method used for evaluating whether an ASD is suitable for interventional therapy should be convenient and accurate. The generally used methods include TTE and TEE.

TTE and TEE provide mainly 2-D images of an ASD. Subsequent processing of images can provide 3-D images. The image quality demonstrated by TTE is usually influenced by factors such as the age, obesity, intercostal space, thoracic deformity and lung diseases. For TEE, because the probe is near the heart, the images are not influenced by the above factors, and in general, clear images of the atrial septum and ASD can be obtained. Nevertheless, TEE has the shortcomings of an observational blind area and causing discomfort in some patients.

TTE examination is relatively easy and convenient. A physician with much experience in echocardiography and interventional therapy in congenital heart disease, through a thorough, multi-view examination with TTE, can, in general, obtain sufficient information about the ASD diameter, shape, position and rims. At present, most hospitals in China use TTE for pre-intervention examination of ASD, but to date, no generally accepted standard exists.

Rao et al18 compared the stretched ASD diameter with 2-D echocardiographic measurements obtained in two subcostal views (long- and short-axis). The echocardiographically measured diameter correlated well with stretched diameter (r=0.82; P <0.001). The stretched diameter could be estimated as the following formula: 1.05 × echocardiographically obtained diameter in millimeters + 5.49. The differences between measured and predicted values were within 2 mm. Therefore, the stretched ASD diameter could be estimated accurately by 2-D subcostal echocardiographic measurement, which in turn could be used for selection of device size for occlusion of the ASD. Jan et al19 obtained a similar formula: the stretched ASD diameter = 1.09 × TTE-measured ASD diameter in millimeters + 3.9.

Zhang20 found good correlation between the diameter of ASD with soft or hard rims with the selected ASO size, but the authors neither illustrated which ASD diameters were measured from several echocardiographic views as the bases for selecting ASO size nor analyzed the potential influences of different ASD diameter ranges on selecting ASO size.

Several studies showed that ASD diameters measured by echocardiography, TTE or TEE, were always 4–6 mm, smaller than that measured by balloon (stretched diameter).9,21

In the present study, before ASD interventional therapy, we used TTE to detect ASD diameter as a routine process to guide ASO size selection and obtained good results. We used multiple views to obtain the largest ASD diameter and used this diameter as the reference for selecting ASO size. For small ASD, because the rims were generally intact, an ASO size a little larger than the ASD diameter measured by TTE was sufficient. However, for a larger ASD, the rims were often soft or not intact and the large ASO weight was also a negative factor for the ASO fixing, so the selected ASO size was much larger than the ASD diameter. We found that an ASD without rims at the ascending aorta side could be closed successfully in most patients.

To guide ASD closure, TEE and ICE are excellent imaging tools.10,11 They can provide good views of the occluder and guide the procedure. But general anaesthesia is needed for TEE. In developing countries, ICE is relatively expensive for most patients to afford. In our study, we used TTE to guide the ASD closure. To ascertain whether the occluder was suitable and fixed, we used the following methods. (1) Observed the ASO shape under X-rays - the two discs' rim should separate well. (2) Push and pull test - pushed and pulled the cable gently; if the occluder was solid, it did not move greatly, so we considered that the occluder was well fixed. (3) Used TTE in different views to observe the occluder position and shape and whether the ASD rims were gripped by the two discs. Obviously, residual shunting should not be accepted. Thus, TTE could be effective, safe and satisfactory in guiding, with the above 3 methods, ASD closure.

In conclusion, TTE used to measure ASD diameter can accurately direct the selection of the ASO needed to successfully close the ASD, especially for relative small ASDs. The larger the ASD, the much larger the ASO needed and the more difficult the intervention procedure. TTE is effective and safe as imaging guide for ASD transcatheter closure.

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Keywords:

transthoracic echocardiography; atrial septal defect; Amplatzer septal occluder; congenital heart disease

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