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Results of Transvenous Occlusion of
Secundum Atrial Septal Defects
P. Syamasundar Rao, MD
Center for Transcatheter Management of
Heart Defects in Children,
Saint Louis University, School of Medicine, Cardinal Glennon Children's Hospital,
St. Louis, Missouri, USA
Congenital heart defects occur in 0.8% of live-born infants. Atrial septal defects (ASDs) constitute 8-13% of such cardiac defects. Surgical closure, described in early 1950s (1-3), has rapidly become a standard therapy. Whereas surgical therapy is safe and effective with nearly no mortality, it has significant morbidity because of necessarily required sternotomy/thoracotomy and cardiopulmonary bypass. Postoperative complications, residual scar of surgery, hospitalization for several days and psychological trauma are additional disadvantages of surgery. Because of these and other reasons, a number of investigators have attempted to develop less invasive, non-surgical, transcatheter approaches to occlude the ASD. Since the initial description by King (4-6), Rashkind (7-9) and their associates of transcatheter closure of ASD, a number of devices have been described, as reviewed elsewhere (10). At the time of this writing, no devices, however, are approved by the US Food and Drug Administration (FDA) for general clinical use. The purpose of this lecture is to review the results of transvenous occlusion of ostium secundum ASDs.
As mentioned previously, a number of devices have been described. Most of the devices have been tested in animal models and clinical trials. Some devices have been discontinued ( ) (6-9,11-21) and others are currently in clinical trials ( ) (22-30). The discontinued devices will not be discussed in this review. Only devices that are currently in clinical trials will be discussed. Detailed description of the devices can be found in the respective papers (22-30) and will only be summarized here ( , ).
Transcatheter occlusion of ASD in the US is performed under a protocol approved by local Institutional Review Boards (IRB) and FDA with investigational device exemption (IDE). In countries outside the USA, the procedure is performed as per local regulations, including approval of local IRBs. Informed consent from the patient or parents, as appropriate is also mandatory.
The indications for transcatheter closure are similar to those used for surgical correction. Ostium secundum ASDs with right ventricular volume overloading (enlarged right ventricle with flat or paradoxical septal motion) are candidates for closure. When cardiac catheterization data are available, a pulmonary-to-systemic flow ratio (Qp:Qs) > (greater or equal) 1.5:1 is generally required. Sinus venosus and ostium primum ASDs are not suitable for transcatheter closure. Also, patients who have developed pulmonary vascular obstructive disease are not candidates for transcatheter occlusion.
Patients with small ASDs and/or patent foramen ovale (PFO) presumably responsible for a) paradoxical embolism resulting in cerebrovascular accidents or transient ischemic attacks (31), b) platypnea-orthodeoxia syndrome (32), c) right-to-left shunting causing hypoxemia (33), including fenestrated Fontan or d) neurological decompression illness in divers (34) are also candidates for device occlusion but, will not be included in this lecture dealing with results of ostium secundum ASD occlusion.
Echocardiographic screening for the size of ASD and septal rims in different views should be undertaken. Precordial echocardiography is usually adequate in children with adequate echo-windows and transesophageal echocardiography (TEE) may be necessary in adolescents and adult subjects. Most double disc devices require at least 3 to 4 mm septal rim, although deficient anterior rim (adjacent to the aorta) is not problematic. While echocardiographic size of the ASD is useful, stretched ASD diameter (35,36) during catheterization is the final determinant of size of the device selected for implantation. Length of the atrial septum determined on echocardiography and/or left atrial cineangiography should be of sufficient size to accommodate the selected device.
The protocol of most devices require general anesthesia and TEE monitoring during device implantation. Complete cardiac catheterization is performed to confirm the clinical and echocardiographic diagnosis and to exclude any associated anomalies, especially partial anomalous pulmonary venous return. Cineangiography from the right upper pulmonary vein at its junction with the left atrium in a left axial oblique view (30° LAO and 30° cranial) to serve as a landmark for use during device implantation is usually performed.
Balloon sizing of the ASD by withdrawal of progressively decreasing sized balloons across the ASD (35,36) has been used in the past. More recently, static sizing of the ASD with a compliant balloon has been described (37) and is used by some investigators. In dynamic sizing (35,36) in vitro measurement of the balloon diameter is used to measure stretched diameter. In both methods, balloon stretched diameter may be measured both by TEE and by cineradiography. It is also important to examine the atrial septum by TEE during balloon occlusion to ensure that there are no additional defects in the atrial septum. The recommended device/defect ratio varies with each device varying from 1.6 to slightly above 2.
The method of implantation is different from
one device to the other, although there are some similarities. The left atrial
disc is initially delivered into the left atrium and under fluoroscopic and
TEE guidance, withdrawn to position it against the left side of the atrial septum
occluding the ASD. The tip of the device delivery sheath is withdrawn further
across the ASD into the right atrium to effect release of the right atrial component
of the device (Amplatzer, Angel Wings II, CardioSeal, StarFlex and Helex) or
an additional right atrial disc (counter-occluder) delivered (Buttoned device).
Following TEE verification of optimal position of the device without interference with other critical structures (pulmonary vein and mitral valve) the device is disconnected ( , ). A final TEE, angiography or hemodynamic evaluation are performed, as per the protocol of that particular device.
The results of transvenous occlusion of ASD with various devices currently in clinical trials will be presented; published multi-institutional trials, when available, will be utilized for this purpose. Feasibility, safety and effectiveness will be examined first, followed by discussion of other issues comparing the devices.
The ratio of number of implantations to the number of subjects taken to the catheterization laboratory with intent to occlude the ASD, the implantation feasibility index, is expected to indicate the facility with which a given device is implantable. Such implantation feasibility varied between 89 to 100% ( ) (28,38-42). A wider range (50 to 100%) was observed in an extensive review of the literature (43). Based on these data, it appears that basic variations of the atrial septal and ASD morphologies appear to have as much of role in determining the implantation feasibility as the devices themselves. In addition, operator experience may play a pivotal role in such determination.
The device or device components may embolize or the device may be misplaced or dislodged. This may occur at the time of the procedure or may take place hours and days after implantation. Rarely, it may be even later. However, most investigators are able to transcatheter retrieve the embolized devices. Occasionally, surgical retrieval becomes necessary. Device dislodgment rates for the currently used devices ( ) are nearly similar.
Cerebrovascular accidents are extremely rare (44) following secundum ASD occlusions. Similarly, formation of thrombus on the device with or without systemic embolization has been reported and some of these appear to be related coagulation factor deficiency. Endocarditis with formation of vegetation has also been reported (45,46), but rare.
Immediate. Evaluation of effectiveness of ASD occlusion is largely performed by the TEE study immediately following device placement and by transthoracic echocardiography within 24 hours of the procedure, prior to discharge. Also, effective occlusion, defined as trivial or no residual shunts (17) is now generally accepted method of evaluation of effectiveness. The effective occlusion rates are also listed in . They vary between 83 to 95% and appear to be similar with all devices currently in use ( ).
Follow-up results. Results at mid-term, defined as 6 to 24 months follow-up are listed in (28,40,47-53). Long-term, defined as mean or median follow-up longer than 24 months is available only for the Fourth generation buttoned device (38) and is also shown in . Residual shunts appear to be lower with Amplatzer and COD buttoned device, while they are higher with CardioSeal and Fourth generation buttoned device. Reintervention rates are variable from one study to the next, appear to be low, varying between 1 to 7.7%. Wire fracture have been reported with CardioSeal (40,52,53) although these appear to be lower than those reported with clamshell device (54,55).
In this section, a brief commentary on the devices currently in clinical trial will be made.
Buttoned device, 4th generation
This is the oldest of the currently used devices and has the largest published clinical experience, thus far. Unbuttoning problem seen with early generations of the device(17) has been resolved by introduction of double button modification (38) and the effective occlusion rate remained unchanged. But, the size of the device has to be at least 2 times as large as the stretched ASD diameter (16). To address this problem, a centering modification was undertaken, which will be discussed later in this section.
Amplatzer septal occluder
This is a relatively new double-disc self-centering device, which can be implanted via small delivery sheath. Rapidly accumulating immediate and short-term data show good occlusion rates. It is easily retrievable and re-positionable prior to disconnecting the device. Thick profile of the implanted device and nickel toxicity have been pointed out as potential problems with this device. Long-term results are necessary to accept its short-term success.
These are re-designed versions of clamshell device. Complete and effective occlusion rates are slightly lower than other devices. Arm fractures continue to exist despite design modifications and is a cause for concern. Long-term follow-up results are needed for further evaluation of these devices.
Guardian Angel device
Clinical trials with this redesigned version of Angel Wings device have not yet started.
This is a new device, appears to be useful in occluding small defects. Immediate results appear to be comparable to other devices. Device implantation technique, though complex, can be mastered. It is retrievable until final release. Follow-up results and experience in larger cohorts are necessary prior to making predictions of its success.
COD Buttoned device
This is a modified rounded 4th generation device with a centering mechanism. Reduction of size of the device without adversely effecting the device dislodgment or occlusion rate has been achieved. Experience in a larger cohort with longer-term follow-up are needed to confirm the early encouraging results.
All the currently used devices are double disc devices with wire components and are therefore subject to limitations and complications associated with such designs. Transcatheter delivered patches also are useful in occluding defects that cannot be closed with conventional double-disc devices. However, there is only a limited clinical experience with these devices. Results of larger international clinical trials and FDA approved (with IDE) human trials are awaited.
SUMMARY AND CONCLUSIONS
Since the initial reports by King, Rashkind and their associates, a large number of devices have been designed and tested for ASD occlusion. Many devices have been discontinued either because the investigators perceived difficulties in continuing further studies or regulatory authorities forced removal of the device from further clinical investigation. Some devices have been modified a number of times to achieve acceptable levels of feasibility, safety and effectiveness. Some devices have large amounts accumulated clinical data and others have limited data, particularly pertaining to long-term effectiveness and safety. None of the devices have yet passed the scrutiny of US approving authority to achieve the status for "general clinical use." Hopefully some of the devices will receive approval within a foreseeable future.
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