(Circulation. 1997;95:2162-2168.)
© 1997 American Heart Association, Inc.
Articles |
Transvenous Closure of Secundum Atrial Septal Defects
Preliminary Results With a New Self-Expanding Nitinol Prosthesis in a Swine Model
From the Departments of Radiology (M.J.A.S., X.G., M.U., J.J.C.-C., K.A.) and Pathology-Laboratory Medicine (J.L.T.), University of Minnesota Hospital and Clinic (Minneapolis), and The Jesse E. Edwards Registry of Cardiovascular Disease (J.L.T.), United Hospital, St Paul, Minn.
Correspondence to Kurt Amplatz, MD, Section of Cardiovascular and Interventional Radiology, Department of Radiology, University of Minnesota Hospital and Clinic, Box 292-Mayo, 420 Delaware St, SE, Minneapolis, MN 55455. E-mail sharafuddinm{at}mirlink.wustl.edu
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Abstract |
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Background Our purpose was to evaluate a new prosthesis for percutaneous closure of secundum atrial septal defects (ASDs).
Methods and Results Percutaneous closure of surgically created fossa ovalis ASD was attempted in 15 minipigs. The mean balloon-stretched ASD diameter was 12.3±2.3 mm (range, 10 to 16 mm). The self-expanding prosthesis was braided from 0.005-in Nitinol wires in the shape of two flat buttons with a short connecting waist with a diameter corresponding to that of the defect to be closed. Polyester filling was added to enhance thrombogenicity. Pulmonary arteriography with levo-phase was obtained before placement; immediately after placement; and at 1-week, 1-month, and 3-month follow-ups. Four animals were killed at 1 week, 1 month, and 3 months for histopathological correlation. Three deaths resulted from ventricular fibrillation (one during anesthesia and two during the placement procedure). Successful placement of the prosthesis was achieved in the remaining 12 animals. Overall immediate ASD closure on angiography occurred in 7 of 12 animals (all polyester-filled prostheses). Absent or trace shunt by angiography was present in 11 of 12 devices at 1 week, with the remaining one demonstrating a small shunt. All septal defects were completely closed at 1 month with the exception of one case in which delayed partial dislodgment of an undersized prosthesis into the right atrium had developed. Closure rate at 3 months was 100%. Neoendothelialization and fibrous incorporation of the prosthesis were completed within 1 to 3 months.
Conclusions Effective and permanent occlusion of secundum ASDs is feasible with a device that offers the advantages of easy placement, self-centering, and repositionability.
Key Words: heart septal defects • heart defects, congenital • pediatrics • shunts
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Introduction |
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Although surgical repair is the procedure of choice for the correction of atrial septal defects (ASDs),1 2 a variety of devices for transcatheter ASD closure have been under development for the past 2 decades.3 4 5 6 7 8 9 10 11 12 13 14 However, most require large delivery sheaths and, on deployment, occupy a large area of the atrial septum, making them unsuitable for use in infants and small children (Table
). Moreover, the majority of
transcatheter occlusion devices require complex deployment
techniques and cannot be recaptured once released from the introducing
sheath, rendering repositioning difficult, if not impossible.
Significant residual shunts, dislodgment, and delayed unbuttoning can
also occur as a result of poor centering, incomplete patching of the
defect, weak anchoring against the septal rim, or mechanical
weakness3 8 11 12 15 16 17 (Fig 1). In this
report, we present our preliminary in vivo experience with a new
self-expanding, self-centering, and recapturable occlusion device that
is delivered through a 6F or 7F sheath, which may allow closure of
secundum-type ASDs in infants or small children.
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Methods |
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Device Design
The study device was constructed from 0.004- to 0.005-in Nitinol wires that are tightly woven into two flat buttons with a 4-mm connecting waist (Fig 2A
through 2C). Because of the
importance of device sizing relative to the defect, prostheses were
constructed in various sizes ranging from 4 to 20 mm in 1-mm
increments (prosthesis size refers to the diameter of the
waist, which should be made to be identical to the measured
balloon-stretched ASD diameter). The two flat retention buttons or
discs extend radially beyond the central waist (5 mm for 10-mm
device, 7 mm for 18-mm device) to provide secure anchorage (Fig 3A and 3B). The two buttons are slightly angled toward each
other to provide firm and secure contact of the prosthesis with
the muscular atrial septal rim (2 to 3 mm thick). The radial span
of the buttons was minimized as much as possible to lower the risk of
encroachment on vital atrial structures (4-mm free margin around the
defect is usually required in children to avoid obstruction of the
ostia of the right upper pulmonary vein and coronary
sinus). The right atrial retention button was made slightly smaller,
taking into account the uniformly present left-to-right pressure
transatrial gradient. Nitinol, a shape memory alloy composed of 55%
nickel and 45% titanium, was used because of its unique superelastic
properties.18 19 The biocompatibility of intravascularly
and surgically implanted Nitinol devices has been well
established.20 21 22 In the last eight procedures, the
prosthesis was filled with fluffy Dacron threads (spun bonded
polyester) sewn into the prosthesis in a pattern identical to
the cords of a tennis racquet (Fig 2C). Because of the high
thrombogenicity, low inflammatory response, and time-tested safety
profile of Dacron as a prosthetic material,23 it
was chosen as a filling material in the device to achieve rapid closure
of the stented defect.
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For introduction, the prosthesis was collapsed and advanced through a simple delivery system consisting of a 6F or 7F thin-walled, nontapered, kink-resistant Teflon introducing sheath and a 0.038-in delivery cable. Occluders of >10 mm were woven from 0.005-in wires and required a 7F introducing sheath, whereas smaller prostheses were woven from 0.004-in wires and could be introduced through a 6F sheath. Before deployment, the prosthesis was attached to the delivery cable with a microscrew connection and withdrawn into a loader for introduction into the delivery catheter. The device was then pushed through the delivery catheter.
Animal Model
All animals were treated according to the "Principles of
Laboratory Animal Care" of the National Society for Medical Research
and the "Guide for the Care and Use of Laboratory Animals" (NIH
publication No. 80-23, revised 1985). The study protocol was
preapproved by the institutional animal care committee. After sedation
of the animals with an intramuscular injection of Telazol (1:1
tiletamine/zolazepam; 8 mg/kg), general anesthesia was
induced through mask inhalation of 1% isoflurane and maintained
through endotracheal inhalation of 1% isoflurane during mechanical
endotracheal ventilation. All chronic experimental procedures were
performed under sterile conditions with continuous ECG monitoring.
A surgical model for the creation of ASD is preferred over
percutaneous transcatheter dilatation of
the foramen ovale to ensure closer resemblance to defects in
humans.13 The choice of the animal species is also very
important to ensure a suitable atrial septal anatomy for the
creation of a secundum-type defect. After a brief initial experience
with surgically created defects in dogs, we abandoned this animal model
because of the poorly developed fossa ovalis and small size of the
atrial septum in the canine. Consequently, a swine model was adopted
because of the well-developed fossa ovalis and comparable atrial septal
anatomy to that of humans, allowing the creation of defects
that closely mimic human secundum ASDs in both size and location.
Nineteen Yucatan minipigs, of either sex and weighing 25 to 30 kg,
underwent surgery for ASD creation. With the animals under general
anesthesia and with the use of sterile conditions, a
transverse left thoracotomy was performed that exposed the heart, and
through a vertical pericardiotomy, clamps were placed across the left
and right atrial appendages; both appendages were entered through
purse-string sutures. The left index finger was inserted into the right
atrium to palpate the fossa ovalis while a sharp punch instrument was
introduced from the left atrial appendage through the purse-string
suture. After being guided to the fossa ovalis with the opposing index
finger, the instrument was thrust through the septum, which was
captured in the instrument and cut with a sliding sharp knife. A 10-mm
cutter was used in all animals, resulting in a mean balloon-stretched
defect diameter of 12.3±2.3 mm (range, 10 to 16 mm). After
creation of the ASD, the chest was closed, and the animal was allowed
to recover for 
1 week before the percutaneous closure
procedure.
Occlusion Technique
With the animal under general anesthesia and with
the use of sterile conditions, transvenous vascular access was
established via cutdown and vascular sheath placement into the femoral
or jugular vein (10 and 2 animals, respectively). Baseline blood gas
and oxygen saturation levels were obtained from the left atrium, main
pulmonary artery, and superior vena cava. The ASD was
visualized through levo-phase pulmonary angiography or direct
left atrial contrast injection. The defect was crossed with an
angiographic catheter, and a J-tipped guide wire was introduced. A
volume-diameter–calibrated 7F Berman balloon catheter was exchanged
over the wire and positioned in the left atrium. The balloon catheter
was inflated with air and pulled back through the defect under
fluoroscopic observation. Slight deformity of the balloon contour
during pullback established the stretched diameter of the septal
defect. The balloon catheter was removed, reinflated with the same
amount of air, and passed through various holes in a sizing plate to
determine the stretched diameter of the defect. Appropriate
prosthesis size was then chosen according to this
balloon-stretched diameter.24 25 The guiding sheath was
introduced through the septal defect over the guide wire. The
prosthesis was attached to the delivery cable and withdrawn
into an adapter tube (loader). The prosthesis was then loaded
into the guiding sheath and advanced through pushing of the delivery
cable. With fluoroscopic guidance, the left atrial button was released
into the left atrium, with care taken to avoid the left atrial
appendage. While constant tension was maintained on the delivery cable,
the right atrial button was then deployed through withdrawal of the
delivery sheath. Proper placement was verified fluoroscopically and
manually, through pushing and pulling on the delivery cable, before the
prosthesis was detached by turning the delivery cable in a
counterclockwise direction with a vice. Misplacement of both buttons
into the left atrium occurred occasionally, which was easily corrected
by recapturing the left atrial button into the guide catheter and
redeploying the device. Pulmonary arteriography and blood gas
measurements were performed after deployment to check for residual
shunt.
Follow-up Studies
Sequential angiographic studies and blood gas measurements were
performed at 1-week, 1-month, and 3-month intervals. With the animal
under general anesthesia, the pulmonary artery was
catheterized via transfemoral or transjugular venous cutdown, and the
atrial septum was imaged in a shallow (15° to 20°) left anterior
oblique projection. Residual shunts were angiographically graded
subjectively by two independent observers and classified as trace
(barely perceptible opacification), small (faint right atrial
opacification with or without faint jet), moderate (obvious right
atrial opacification less than the left atrium with or without a
clearly visible jet), or large (bright right atrial opacification).
Comparisons of shunt closure rates after device placement and of mean
Qp/Qs ratios before closure, immediately after
closure, and on follow-up were performed using a two-tailed nonpaired
Student's t test. Transthoracic
echocardiography with color Doppler was also
used in a number of animals during placement and on follow-up
examinations.
Histopathological Correlation
Animals were killed after 1 week, 1 month, or 3 months (four
animals per time interval). The heart and great vessels were explanted
and fixed in a buffered physiological solution
containing 10% formaldehyde or 2% glutaraldehyde for
histopathology or scanning electron microscopy.
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Results |
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Mortality
A total of 19 minipigs underwent surgery for ASD creation. Four animals died during surgery as a result of fatal ventricular fibrillation. An additional animal developed fatal dysrhythmias (third-degree atrioventricular block progressing to refractory ventricular fibrillation) during general anesthesia before the closure procedure was attempted. Postmortem examination in that animal showed a large defect (15 mm diameter). Death occurred in 2 animals during device placement due to refractory ventricular fibrillation. In the remaining animals, there were no significant ECG changes, and there was no postprocedural mortality.
Technical Success
Percutaneous closure of surgically created defects
of the fossa ovalis was attempted in 15 minipigs. As mentioned, 3
animals died as a result of ventricular fibrillation, with
one death occurring during anesthesia. In the remaining 12
animals, placement of the prosthesis was successful, resulting
in an overall success rate of 85% (12/14) and a technical success rate
of 100%. The mean balloon-stretched ASD diameter was 12.3±2.3 mm
(range, 10 to 16 mm), whereas the mean device waist diameter was
11±2.3 mm (range, 8 to 16 mm). The addition of Dacron
filling slightly increased the resistance to the initial advancement of
the device through the introducing sheath but did not appreciably alter
the ease of deployment. Successful deployment was independent of the
approach (transjugular or transfemoral) or the angle of attack. Once
the ASD was crossed, placement of the device could be accomplished in
<1 minute.
Preclosure angiography demonstrated a large left-to-right atrial shunt
in all animals, with a corresponding mean Qp/Qs
ratio of 1.7±0.55. Immediately after the placement of the
prosthesis, complete closure of the defect on angiography was
noted in 7 of the 12 animals (58%) (Fig 4), whereas the
remaining animals demonstrated only small shunts. Significant lowering
of the mean Qp/Qs ratio occurred immediately
after device placement (1.0±0.15, P<.02). Significantly
higher immediate closure rates were achieved with polyester-filled
prostheses compared with rates for nonfilled prostheses (86% versus
0%; P=.018). A tendency toward a higher rate of immediate
closure was also noted when the prosthesis waist diameter
closely fit the defect (87%) compared with prostheses that were
undersized by >3 mm (33%). However, the difference did not reach
statistical significance (P=.09), which is probably the
result of the small sample size.
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Angiographic Follow-up
Follow-up angiography at 1 week demonstrated complete angiographic
shunt closure in 8 of 12 animals (67%), whereas persistent trivial
shunts were demonstrated in 3, and persistent small shunts were
demonstrated in the remaining animal. Angiographic follow-up of 8
animals, in which follow-up was available at 1 month after device
placement, showed complete shunt closure in all except 1 animal (88%
closure rate), in which angiography showed the prosthesis to
have become partially dislodged into the right atrium with a large
residual left-to-right atrial shunt. In that animal, a 10-mm-diameter
device had been placed across a 16-mm defect because of the
unavailability of a larger device at that time. Three-month
angiographic follow-up, which was available in 4 animals, showed
complete closure in all (100% closure rate). The mean
Qp/Qs ratio on the various follow-up intervals
showed no significant difference from the immediate postplacement value
(mean difference, 0.02 to 0.2; P>.1).
Pathology
The device occupied the region of the fossa ovalis in all animals,
with the exception of one device found at 1 month to be partially
dislodged into the right atrium. In all cases, there was no compromise
of the orifices of the left pulmonary veins, coronary
sinus, or other vital atrial structures by the retention buttons of the
device.
Four specimens were examined at 1 week after device placement. Three of the devices used in these specimens were not filled with polyester fibers. The wire mesh of the polyester-filled prosthesis was completely invested by a layer of organizing fibrin. Complete or near-complete coverage of the wire mesh with organizing fibrin thrombus occurred in two nonfilled devices, whereas the remaining one was only partially covered. Two of the nonfilled prostheses were patent to manual probing.
Postmortem gross and microscopic examination of seven devices at 1 to 3
months after placement showed complete or near-complete neoendocardium
coverage of both the right and left atrial discs. On visual inspection,
a smooth, shiny, glistening pseudoendocardium was found to cover both
aspects of the prosthesis (Fig 5). One device,
found at 1 month to be partially dislodged, demonstrated only partial
endothelialization and a firm fibrous connection with
the atrial septum along its inferior margin. Examination
with scanning electron microscopy in one specimen showed both surfaces
of the device to be completely covered with flat
neoendothelial cells, continuous with the endocardium
of the surrounding atrial septal rim.
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The lungs did not have emboli or other abnormalities on gross morphological inspection in any of the cases.
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Discussion |
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The described prosthesis represents a departure from prior ASD occlusion devices (Table
). It was designed to avoid many
of the limitations of prior devices, such as large delivery systems,
cumbersome placement, poor centering, oversized device profile, and
inability to recapture. It can be introduced through a 6F or 7F
delivery sheath (7F sheath is required for devices of >10 mm).
The use of a Nitinol wire-mesh construction provides reliable
expansion. The small delivery system and low profile after deployment
render this prosthesis suitable for use in pediatric patients.
Currently available devices rely on large retention flanges to patch
the ASD and require large delivery systems. The clamshell, Sideris, and
ASDOS prostheses require a 2- to 2.5-fold larger device than the
diameter of the septal defect to overcome the effect of preferential
eccentric positioning in the defect.4 8 11 Large
prosthesis dimensions are also required by the
ASDOS4 and the self-centering Das double-patch
device.12 As a result, a substantial proportion of
pediatric patients are not candidates for closure with these devices.
Only 
50% of secundum ASDs were found to be amenable to closure with
the clamshell device.26 The presented
prosthesis requires the presence of a smaller septal rim around
the defect, which is <70% of that required with the clamshell
occluder. Current ASD closure devices primarily accomplish closure
through the application of a patch to the defect, which may not
completely adapt to the variable thickness of the septal rim,
particularly with devices in which the retention flanges are widely
separated24 25 (Fig 1B). The failure of patch-type devices
to maintain firm contact with the endocardium may retard or
prevent complete epithelialization.9 27 Recently, the
ASDOS was introduced, which uses a screw-type tightening mechanism to
ensure tight cross-patching.4 The present device uses
a different mechanism. It was constructed with inward inclination of
the retention discs and slightly smaller right atrial retention disc to
allow firm cross-clamping against the septal rim (Fig 3). Based on
measurements that we previously made in normal hearts in which the
diameter of most muscular atrial septa varied from 2 to 3.5 mm
(unpublished data), the retention discs in the device were separated by
a 4-mm tubular waist filled with polyester fibers to induce thrombosis.
This short communication waist should be sized to ensure firm stenting
of the defect so that blood crossing beyond the disc portion of the
device has to pass through this thrombogenic polyester-filled channel.
Precise measurement of the defect size is therefore of paramount
importance to ensure the highest immediate closure rates. The device is
presently being made in various sizes ranging from 4 to 20 mm
in diameter, at 1-mm increments. Because many ASDs are not round, the
echocardiographic measurement of the defect diameter
may be misleading. Therefore, the diameter of the device should be
selected only according to the balloon-stretched diameter of the ASD to
ensure tight stenting of the defect with the prosthesis waist,
which is an essential component of the closure mechanism. Nevertheless,
echocardiographic evaluation before closure remains
essential to map the ASD location, rule out additional septal defects
or fenestration, rule out anomalous venous connections, and determine
the overall suitability for percutaneous
closure.9 25 26 28 Echocardiography
can also play an important role in guiding the deployment of the
device.4 Device dislodgment can occur if the size of the defect greatly exceeds the waist diameter of the device or approaches the diameter of the retention buttons, as did occur in 1 animal in our study. On the other hand, placement of a disproportionately large device may result in mushrooming of the retention buttons and weakening of the cross-clamping forces against the septal rim, which increases the risk of blood flow behind the discs and may result in incomplete endothelialization.
Follow-up studies of the clamshell occlusion device reported a
delayed rate of metal fatigue fractures of one or more arms of
30%.3 However, unlike acute device failure that occurs
as a result of frame or strut fractures,16 delayed device
fracture usually poses little clinical significance provided that no
fragmentation or embolization ensues. Fatigue fractures that occur as a
result of repetitive bending (100 000 cardiac contractions per day)
are less likely to occur with the presented device because of
the low profile and round configuration of the retention discs, which
do not extend to the free atrial wall. This configuration should also
reduce the risk of atrial perforations compared with designs with
struts or sharp corners, which can come in contact with the atrial wall
during cardiac contraction. Another important factor preventing
mechanical failure with the presented device is the exceptional
strength and high energy-absorbing capacity of Nitinol,29
which enable it to dissipate four times more strain compared with steel
alloy.30 Furthermore, the densely intermeshed wire network
should reduce the risk of embolization in case of wire breakage.
Although a primarily angiographic follow-up was used in our study, echocardiography with color Doppler may be better suited in clinical applications, both during device placement as an adjunctive cross-sectional imaging modality to assess the relation of the prosthesis to vital atrial structures and for postplacement follow-up of residual shunts and device position.4 11
In conclusion, the small introduction system, simple and reliable placement technique, and favorable initial experimental success demonstrate the promising potential of this device for the percutaneous closure of secundum ASDs in all age groups. The device is also being modified to allow treatment of muscular ventricular septal defects. Anticoagulation was not used in our experiments. However, heparinization is advocated in clinical use to lower the risk of catastrophic systemic embolization.27 31 At present, the main drawbacks of the presented device include the requirement of accurate defect sizing, small number of animals used in the present study, lack of adequate long-term follow-up, and limited clinical experience.
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Acknowledgments |
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The authors are grateful to Eric Solien for his surgical skills in performing the animal model and Jim Berry for his echocardiographic assistance.
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Footnotes |
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Dr Sharafuddin's current address: Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63144.
Received June 24, 1996; revision received November 18, 1996; accepted November 21, 1996.
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J. Masura, P. Gavora, and T. Podnar Long-term outcome of transcatheter secundum-type atrial septal defect closure using Amplatzer septal occluders J. Am. Coll. Cardiol., February 15, 2005; 45(4): 505 - 507. [Abstract] [Full Text] [PDF]
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C. Massimo, B. Gianfranco, and C. Mario Risk of thrombus formation on devices used to close transcatheter atrial septal defect and patent foramen ovale J. Am. Coll. Cardiol., October 19, 2004; 44(8): 1712 - 1712. [Full Text] [PDF]
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J. W. Moore and D. S. Levi Transcatheter closure of atrial shunts: Focus on a lingering issue J. Am. Coll. Cardiol., January 21, 2004; 43(2): 310 - 312. [Full Text] [PDF]
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M. Zanchetta, E. Onorato, G. Rigatelli, L. Pedon, M. Zennaro, A. Carrozza, and P. Maiolino Intracardiac echocardiography-guided transcatheter closure of secundum atrial septal defect: A new efficient device selection method J. Am. Coll. Cardiol., November 5, 2003; 42(9): 1677 - 1682. [Abstract] [Full Text] [PDF]
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G Fischer, J Stieh, A Uebing, U Hoffmann, G Morf, and H H Kramer Experience with transcatheter closure of secundum atrial septal defects using the Amplatzer septal occluder: a single centre study in 236 consecutive patients Heart, February 1, 2003; 89(2): 199 - 204. [Abstract] [Full Text] [PDF]
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C. Rickers, M. Jerosch-Herold, X. Hu, N. Murthy, X. Wang, H. Kong, R. T. Seethamraju, J. Weil, and N. M. Wilke Magnetic Resonance Image-Guided Transcatheter Closure of Atrial Septal Defects Circulation, January 7, 2003; 107(1): 132 - 138. [Abstract] [Full Text] [PDF]
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Z.-D. Du, Z. M. Hijazi, C. S. Kleinman, N. H. Silverman, K. Larntz, and Amplatzer Investigators Comparison between transcatheter and surgical closure of secundum atrial septal defect in children and adults: Results of a multicenter nonrandomized trial J. Am. Coll. Cardiol., June 5, 2002; 39(11): 1836 - 1844. [Abstract] [Full Text] [PDF]
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P. S. Rao, F. Berger, C. Rey, J. Haddad, B. Meier, K. P. Walsh, J. S. Chandar, T. R. Lloyd, J. Suarez de Lezo, R. Zamora, et al. Results of transvenous occlusion of secundum atrial septal defects with the fourth generation buttoned device: comparison with first, second and third generation devices J. Am. Coll. Cardiol., August 1, 2000; 36(2): 583 - 592. [Abstract] [Full Text] [PDF]
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Y V Maeno, L N Benson, P R McLaughlin, and C Boutin Dynamic morphology of the secundum atrial septal defect evaluated by three dimensional transoesophageal echocardiography Heart, June 1, 2000; 83(6): 673 - 677. [Abstract] [Full Text]
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K C Chan, M J Godman, K Walsh, N Wilson, A Redington, and J L Gibbs Transcatheter closure of atrial septal defect and interatrial communications with a new self expanding nitinol double disc device (Amplatzer septal occluder): multicentre UK experience Heart, September 1, 1999; 82(3): 300 - 306. [Abstract] [Full Text] [PDF]
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Z. Amin, X. Gu, J. M. Berry, J. L. Bass, J. L. Titus, M. Urness, Y.-M. Han, and K. Amplatz New Device for Closure of Muscular Ventricular Septal Defects in a Canine Model Circulation, July 20, 1999; 100(3): 320 - 328. [Abstract] [Full Text] [PDF]
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Z. Amin, A. P Rocchini, and D. F Wax Closure of Residual Shunts After Fontan Operation With Amplatzer Occluder Asian Cardiovasc Thorac Ann, June 1, 1999; 7(2): 121 - 123. [Abstract] [Full Text] [PDF]
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B. D. Thanopoulos, G. S. Tsa |