EXPEDITED REVIEW
Intracardiac echocardiography-guided transcatheter closure of secundum atrial septal defect
A new efficient device selection method
Mario Zanchetta, MD*,*,
Eustaquio Onorato, MD ,
Gianluca Rigatelli, MD*,
Luigi Pedon, MD*,
Marco Zennaro, MD*,
Antonio Carrozza, MD* and
Pietro Maiolino, MD*
* Department of Cardiovascular Disease, Cittadella General Hospital, Via Riva Ospedale, Padua, Italy
Division of Cardiology, Humanitas Gavazzeni, Bergamo, Italy
* Reprint requests and correspondence to: Dr. Mario Zanchetta, Dipartimento di Malattie Cardiovascolari, Ospedale Civile, Via Riva Ospedale, 35013, Cittadella, Padova, Italy.
emodinacit{at}ulss15.pd.it
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Abstract
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OBJECTIVES: We assessed the use of intracardiac echocardiography (ICE) as the primary means for both selection of the Amplatzer Septal Occluder (ASO) and the guidance of transcatheter closure of secundum atrial septal defects (ASDs).
BACKGROUND: The standard method for transcatheter closure of ASDs requires balloon-sizing maneuver and transesophageal echocardiographic (TEE) monitoring. The role of ICE during transcatheter closure of ASDs has not yet been established.
METHODS: In 91 patients with ASDs, two standardized orthogonal sections were used to obtain ICE-derived measurements of the fossa ovalis and to assess optimal device deployment: the transverse section on the aortic valve plane, and the longitudinal section on the four-chamber plane.
RESULTS: In all patients, ICE planes were identified with excellent resolution, providing proper measurements of the fossa ovalis, from which to derive geometric assumptions for the selection of an appropriately sized device. The ASO waist diameter was chosen on the basis of the r value (r = c2 + p2, where r is the radius of an ideal circle that intersects the elliptical fossa ovalis in its semi-latus rectum, c is the foci half-distance of the fossa ovalis, and p is its semi-latus rectum). During the procedure, the four-chamber plane allowed us to obtain easily interpretable images of all stages of device deployment. Midterm complete occlusion rate was 97.8%. No ICE-related complications occurred.
CONCLUSIONS: The ICE evaluation of ASDs allows quantitative and qualitative information for both proper ASO selection and optimal device placement, thus eliminating the cumbersome balloon-sizing maneuver and the need for general anesthesia during TEE monitoring.
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Abbreviations and Acronyms
| | ASD | = secundum atrial septal defect | | ASO | = Amplatzer Septal Occluder | | ECG | = electrocardiography | | ICE | = intracardiac echocardiography | | TEE | = transesophageal echocardiography |
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The universally accepted and most frequently used methods for Amplatzer Septal Occluder (ASO) device selection and deployment include balloon-sizing maneuver (1,2) and transesophageal echocardiography (TEE) monitoring (3,4). However, both of these methods have their drawbacks. On the one hand, balloon-sizing is a blind technique that cannot provide delineation on site, on shape, and on the dynamic geometry of the secundum atrial septal defect (ASD), or provide information on characteristics of the surrounding structures; moreover, it can be somewhat inaccurate, sometimes causing oversizing or undersizing of the device (5). On the other hand, TEE is a technique that may not be indicated in all patients in which the majority requires general anaesthesia with or without endotracheal intubation, owing to the poor acceptance of an esophageal probe for the entire duration of the procedure; furthermore, the risks of aspiration, airway obstruction, esophageal perforation, and vocal cord dysfunction have been reported, although infrequently (6,7).
Over the past several years, intracardiac echocardiography (ICE) has been used in the descriptive evaluation of the atrial structures to facilitate trans-septal puncture (8,9), to guide radiofrequency ablation lesions (10–12), and to provide a practical approach for precise determination of left ventricular function (13) and aortic valve area (14). On the basis of these previous studies, investigators explored, in an in vitro model, the possibility of an accurate and reliable evaluation of the size of ASDs by ICE (15). More recently, interventional cardiologists have performed ICE using both electronic multi-element (16) and mechanical single-element (17) systems in the cardiac catheterization laboratory during transcatheter closure of ASDs, finding a significant correlation between ICE and the other conventional methods; however, the definitive confirmation of ASO selection was based on the balloon-sizing technique.
This study describes the use of ICE alone to monitor and guide transcatheter closure of ASDs using ASO, thus eliminating the cumbersome balloon-sizing maneuver and the need for general anesthesia or deep sedation during TEE monitoring.
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Methods
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Study patients.
Between July 2000 and November 2001, a total of 91 consecutive eligible patients with hemodynamically significant ASDs (34 male and 57 female; mean age 49.2 ± 14.8 years, range 15 to 73 years) underwent transcatheter closure using the ASO (AGA Medical Corp., Golden Valley, Minnesota) under fluoroscopy and ICE guidance without use of the balloon-sizing maneuver. A full description of the device has been reported previously (3,4,18). The local ethical committee approved the protocol, and written informed consent was obtained from all patients or their respective guardians.
ICE
The ICE was performed by the same interventional team (single operator use) using a commercially available 9F–9MHz Ultra ICE catheter-based ultrasound transducer (EP Technologies, Boston Scientific Corp., San Jose, California), as previously described (19). The axial and the lateral resolutions were 0.27 mm and 0.26 mm, respectively, whereas the radial imaging depth of penetration was about 5 cm.
The Ultra ICE catheter was introduced percutaneously into the left femoral vein through a 55° precurved polyethylene long venous sheath (Convoy, EP Technologies, Boston Scientific Corp.). Two standardized orthogonal sections were used to obtain ICE-derived fossa ovalis measurements and to assess optimal device deployment: the transverse section on the aortic valve plane in the short-axis of the body, and the longitudinal section on the four-chamber plane in the long-axis of the heart. The latter view was also used to monitor all stages of the device deployment.
The transverse section was obtained with the precurved sheath withdrawn to the infrarenal portion of the inferior vena cava and the Ultra ICE catheter neutrally positioned under fluoroscopic guidance in the body of the right atrium, with the transducer at the level of 6° to 7° intervertebral thoracic disk, to transversally scan the atrial septum on the aortic valve plane. By convention (19), this image was electronically rotated and presented in a consistent and familiar orientation identical to that of a magnetic resonance imaging format, with left-sided structures on the operator's right, anterior-sided structures at the top of the image, and so forth.
The longitudinal section was obtained with the 55° precurved introducer sheath advanced up to the end of the catheter and turned posterior and leftward astride the defect under fluoroscopic guidance so as to scan the atrial septum in its long-axis. The resultant image replicated the apex-up four-chamber TEE and magnetic resonance views, without the need for image reorientation. Real-time cross-sectional images (30 frames/s) were recorded on super-VHS videotapes for off-line archiving and review.
The major (2a) and the minor (2b) axes of the fossa ovalis (i.e., septum secundum-to-septum secundum distance) on these two orthogonal planes were measured by two blind observers, using end-diastolic frames. By assuming its shape to be an ideal ellipse (Fig. 1) , we calculated the following data (Appendix): the ellipse eccentricity ( , where e may be defined as the ratio of the distance from the center to a focus and the distance from the center to an end point of the major axis), the foci half-distance  , where c may be defined as the half-distance between the two points called foci, the sum of whose distances from any point on the ellipse is constant), the semi-latus rectum distance ( , where p may be defined as the chord through a focus parallel to the directrix of the ellipse), and the ellipse perimeter (PFO) and area (AFO). From these data, we calculated the radius of an ideal circle (Fig. 2) that intersects the elliptical fossa ovalis in its semi-latus rectum (r), the circumference (CASO) and area (AASO) of this ideal circle, whose values are equal to that of the waist of the implanted ASO. This ideal-derived circle is the only one that might be in a constant and repetitive manner determined for any given ellipse, and it is the one that may best fit the elliptical shape of ASDs because its circumference and area are equal to the same approximate precision to the ellipse perimeter and area. In fact, the size of the waist of the ASO was chosen exclusively on the basis of the r value, speculating that coexistent septum primum tissue within the fossa ovalis could not adequately support the device, whereas the radial force of its waist could easily distend it.
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Figure 1 Geometry of an ellipse. In our example here, the ellipse is longer in the horizontal direction: this length is called the major axis and the up-and-down width is called the minor axis. Two distinct fixed points can be identified on the major axis, called foci and marked F and F', the sum of whose distances from each point on the ellipse is constant. The distance across the ellipse at the focal point is called the latus rectum. The semi-major axis is labeled a, the semi-minor axis b, the half-focal distance c, and the semi-latus rectum p.
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Figure 2 Conceptual circle that best fits an ellipse. An ellipse (red line) can be constructed by drawing two concentric circles (black lines): the radius of the inscribed circle defines the semi-minor axis (b), whereas the radius of the circumscribed circle defines the semi-major axis (a). From c and p values, the radius (r) of the circle that intersects the ellipse in its semi-latus rectum (blue line) can be computed.
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Before and after the release of the prosthesis, its correct positioning was judged in the two orthogonal sections using qualitative ICE criteria, such as coverage of the entire fossa ovalis, adequate anchoring of the prosthesis on the muscular septum secundum, symmetrical expansion of the two retention disks, correct alignment of the device to the atrial septum, and no interference of the device with neighboring structures.
Closure protocol and follow-up
Routine examination before the procedure included electrocardiography (ECG), chest X-ray, and transthoracic echocardiography. The ASO deployment was carried out as described elsewhere (2–4,18), with the only modification that the procedure was done under ICE guidance alone, without performing balloon-sizing maneuver and TEE monitoring. The patients received heparin 70 IU/kg during the procedure, followed by aspirin for six months; infective endocarditis prophylaxis was also recommended for the same period. Before discharge, ECG, chest X-ray and transthoracic echocardiography were performed and scheduled at 1 and 3 months after device implantation, whereas TEE was performed at 12 months. The residual shunt was classified by color Doppler echocardiography study, according to criteria by Boutin et al. (20).
Statistical analysis
Data were expressed as mean value ± SD, and in percentages where appropriate. The SPSS PC 11.0 software package for Windows (SPSS Inc., Chicago, Illinois) was used for statistical analysis.
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Results
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Ninety-two ASOs were successfully implanted in 91 patients during the study period. One of the patients received two ASOs owing to distant location of multiple holes within the atrial septum; the largest device was first deployed, and the smaller second device did not overlap the first.
Adequate quality of ICE images (Figs. 3A and 3B) for measurements of the semi-major (a) and semi-minor (b) axes of the fossa ovalis on the two orthogonal planes could be obtained in all patients (Table 1) , with interobserver variability calculated  3%.
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Figure 3 Transverse section on the aortic valve plane (A), and longitudinal section on the four-chamber plane (B) in a patient with secundum atrial septal defect (ASD). The major and minor axes of the fossa ovalis can be accurately evaluated by intracardiac echocardiography (ICE): a = 9.8 mm and b = 9.3 mm. The r value is computed as follows: c = 9.82 – 9.32 = 3.090 mm, p = 
= 8.825 mm, r = 3.0902 + 8.8252 = 9.35 mm, where c is the foci half-distance, p is the semi-latus rectum distance, and r is the estimated radius of the ICE-derived Amplatzer Septal Occluder (ASO). In this case, we implanted a 19-mm ASO. AoD = descending aorta; LA = left atrium; MV = mitral valve; RA = right atrium; RUPV = right upper pulmonary vein; TV = tricuspid valve.
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The basic properties of ellipse suggested a roundish elliptical shape of the fossa ovalis rather than an elongated one. In fact, the eccentricity was low, the foci half-distance were approximately one-half of the semi-major axis, and the semi-latus rectum distance was close to the semi-minor axis.
An excellent correlation was found between the value for the calculated perimeter and area of the fossa ovalis and the estimated circumference (y = 1.03x – 1.42, r2 = 0.98, p < 0.001, slope = 0.94) and area (y = 1.05x – 17.08, r2 = 0.97, p < 0.001, slope = 0.92) of the ideal circle that intersects the elliptical fossa ovalis in its semi-latus rectum. Nevertheless, the perimeter and circumference values (Online-only Appendix: Equations 4 and 6) had a better approximation than did those of the area (Online-only Appendix: Equations 5 and 7) as the area changes much more than the perimeter, when a circle is the degenerate case of an ellipse.
Moreover, the ICE-derived radius value of the circle that intersects the elliptical fossa ovalis in its semi-latus rectum was used to choose the waist of the ASO, equalling the same ±1 mm the 2r value in all cases.
The longitudinal four-chamber plane was capable of providing clear and easily interpretable images of the entire procedure, adequately replacing the two-dimensional features of TEE (Fig. 4) in all 91 patients. Before and after the release of the prothesis, the device and surrounding structures were interrogated by ICE in the two orthogonal planes. No encroachment of the device occurred on atrioventricular valves, on right pulmonary veins, or on the superior and inferior caval veins; in addition, complete coverage of the fossa ovalis and the alignment of the prosthesis to the septum were assessed in all cases. An overestimation of the ASO size leading to a bulgy appearance occurred in one patient, but we decided not to replace the device owing to the satisfactory result.
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Figure 4 Longitudinal section on the four-chamber plane of an implanted ASO. Note how both disks are clearly visible, thanks to the optimal echogenicity and the characteristic "multiple ray" pattern of the prosthesis. The released device acquires a flat shape and covers the entire fossa ovalis. Abbreviations as in Figure 1.
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The procedural times ranged from 34 to 77 min (mean 55.3 ± 21.6 min) and the fluoroscopy times ranged from 5 to 17 min (mean 11.9 ± 6.2 min), and they were not statistically different from those of our previous series using TEE. No complications such as device embolization, thromboembolic events, or pericardial effusion occurred during the procedure or at the time of follow-up examinations, which ranged from 12 to 28 months (mean 401 days); in particular, no ICE-related complications occurred. The rates of complete occlusion were 97.8% (89/91) at 1 year.
During the total follow-up, a small shunt decreased to a trivial one in one patient, whereas a small shunt appeared at the three-month follow-up in another patient with initial complete closure. Subsequent TEE, ICE, and cardiac catheterization confirmed minor displacement of the device with part of the left retention disk partially protruding to the right atrium. Notwithstanding, the right ventricular end-diastolic diameter was decreased, indicating effective abolishment of right heart overload, and the patient did not undergo surgical removal of the device.
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Discussion
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Transcatheter closure of ASDs has recently gained wide acceptance and has become an increasingly attractive alternative to surgical repair in selected cases. The unique features of the ASO have extended the limits of transcatheter closure (21–23) with promising short-term and midterm results (3,4). However, an extremely precise assessment of ASDs is crucial for optimal ASO selection and procedural success.
In the absence of a gold standard, the balloon-sizing of the defect, performed using both the pulling and stationary techniques, is the most commonly used method to assess size of ASDs. However, balloon-sizing is far from being accurate, and this may be associated with certain pitfalls. First, balloon-sizing, especially if done repeatedly, can itself cause damage, enlarging the defect by tearing the flap valve of the septum primum. Second, the estimated stretched diameter cannot determine the actual dimension of the defect, and this mainly depends on the force applied in retrieving the balloon through the defect and on the angle of balloon popping through the septum. Finally, balloon-sizing may cause arrhythmias or obstruction of venous return, although such complications are rare.
In this study, we have seen that ICE allows a proper measurement of the fossa ovalis and an appropriately sized device selection, also facilitating all stages of the deployment process monitoring. The availability of only two-orthogonal views and of no-color Doppler capability have to be considered the major disadvantages of the mechanical transducer in comparison with the electronic one, and the derivation of quantitative data from geometric assumptions could be interpreted as the major limitation of our study. Although recent technologic advances have made it feasible to use three-dimensional TEE (24,25) and magnetic resonance imaging (26,27) to evaluate ASDs directly, they are not currently or readily available for online clinical use in the catheterization laboratory. Moreover, it is our opinion that color-flow Doppler capability is not strictly necessary. On the one hand, immediate residual shunt is demonstrated on TEE in the vast majority of cases, and complete occlusion of the defect can require hours, days, or even months (3,28–31). On the other hand, by selecting ASO based on the fossa ovalis measurement and not on the defective area, it ensures stable anchoring of the device into the muscular septum secundum, thus reducing the possibility of periprosthetic leaks.
Previous experiences have confirmed that ICE is an extremely useful method to evaluate ASDs in patients undergoing transcatheter closure by an ASO, and have also provided the basic accuracy of the technique (16,17). The current study adds a new and quantitative use for ICE imaging with several clinical implications. First, it proposes two standardized planes for accurate measurements of the major and minor axes of the fossa ovalis. Second, it defines a calculation process, also available in a simple software program, for the selection of an ASO device, thus eliminating the cumbersome balloon-sizing maneuver. Third, it identifies the ICE four-chamber section as a view that can replace TEE monitoring during the procedure, thus abolishing the need for general anesthesia or sedation, without additional patient discomfort. Fourth, ICE imaging establishes the safety and feasibility of using ICE alone as an adjunct to fluoroscopy and as the primary means of transcatheter closure of ASDs: with this approach, patient acceptance of the procedure increases, and the results are comparable to those reported by use of the conventional methods. Fifth, our mathematical model supports the accuracy of ICE-derived fossa ovalis evaluation, suggesting to proceed with the transcatheter closure of ASDs only in case of roundish elliptical fossa ovalis so as to avoid improper deformation of the circular waist of the ASO when it is stretched into the minor axis of the fossa ovalis ("mushrooming" appearance) and to prevent periprosthetic leaks, which may occur across its major axis if the fossa ovalis has an elongated shape. Finally, for the successful closure of an ASD on ICE guidance alone, the unique self-centering ability of the ASO is fundamental, and this strategy is not suitable for other devices.
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APPENDIX
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For the Appendix, please see the November 5, 2003 issue of JACC at http://www.cardiosource.com/jacc.html.
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Abstract
Methods