DOI:10.2214/AJR.06.0709
AJR 2007; 188:W431-W439
© American Roentgen Ray Society
MDCT Evaluation After Closure of Atrial Septal Defect with an Amplatzer Septal Occluder
Tain Lee1,2,3,
I-Chen Tsai1,2,3,4,
Yun-Ching Fu3,4,5,
Sheng-Lin Jan5,
Chung-Chi Wang6,
Yen Chang6 and
Min-Chi Chen1
1 Department of Radiology, Taichung Veterans General Hospital, Taichung Harbor
Rd., Taichung 407, Taiwan, Republic of China.
2 Faculty of Medicine, Medical College of Chung Shan Medical University, Taiwan,
Republic of China.
3 Department of Medicine, National Yang Ming University, Taiwan, Republic of
China.
4 Institute of Clinical Medicine, National Yang Ming University, Taiwan,
Republic of China.
5 Section of Pediatric Cardiology, Department of Pediatrics, Taichung Veterans
General Hospital, Taiwan, Republic of China.
6 Section of Cardiovascular Surgery, Department of Surgery, Taichung Veterans
General Hospital, Taiwan, Republic of China.
Received May 26, 2006;
accepted after revision November 21, 2006.
Address correspondence to I.-C. Tsai
(sillyduck{at}vghtc.gov.tw).
Tain Lee and I-Chen Tsai contributed equally to this study.
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Abstract
OBJECTIVE. The essay describes the protocol for and interpretation
of MDCT scans in the evaluation of patients after insertion of an Amplatzer
septal occluder.
CONCLUSION. In anatomic regions that cannot be confidently evaluated
with transthoracic echocardiography, MDCT is useful for evaluating Amplatzer
septal occluders for protrusion, migration, and residual shunt. Radiologists
should be familiar with the imaging protocol and interpretation.
Keywords: cardiac imaging • cardiovascular disease • congenital malformations • CT
Introduction
Closure of an atrial septal defect (ASD) with an Amplatzer septal
occluder (AGA Medical Corporation) entails a shorter hospital stay and is less
invasive than surgery [1]. If
accompanied by intracardiac echocardiography rather than transesophageal
echocardiography, closure with this device can be performed without general
anesthesia [2]. For this
reason, the Amplatzer septal occluder has gradually been recognized as an
important alternative for closure of secundum-type ASD. Patient acceptance is
high. After the procedure, transthoracic echocardiography (TTE) usually is
used for follow-up to check for migration, protrusion, and residual shunt.
Because of the highly echogenic nature of the occluder, however, and the
limited acoustic window in adult patients, some small defects are not
visualized with confidence even with color Doppler technique. In such
circumstances, MDCT can be used for further evaluation. We describe the
imaging protocol for and interpretation of MDCT follow-up images after
insertion of an Amplatzer septal occluder. Except for pediatric radiologists
in specialized centers, most radiologists may not be familiar with the
Amplatzer septal occluder
[1-5].
Harper et al. [5] review
current concepts. The composition and design of the device are described on
the manufacturer's Website
(www.amplatzer.com).
Materials and Methods
Cardiac CT Protocol
The records of all patients who underwent insertion of an Amplatzer septal
occluder and were referred for cardiac CT between January 2005 and April 2006
were retrospectively reviewed. Before CT, these patients were evaluated with
TTE, the findings of which suggested protrusion, migration, or the presence of
residual shunt.
Oral propranolol (Cardilol, Veterans Pharmaceutical Factory) at 0.5 mg/kg
body weight was given 1 hour before MDCT to reduce heart rate. Imaging was
performed with a 40-MDCT scanner (Brilliance 40, Philips Medical Systems) and
a dual-syringe injector (Stellant, Medrad). The parameters were tube voltage
of 120 kV, weight-based effective tube current adjustment of 150-700 mAs per
section, collimation of 40 x 0.625 mm, rotation time of 0.4 seconds, and
pitch of 0.2 with retrospective ECG gating. The scan was starting from 0.5 cm
below the carina to the end of the heart in the craniocaudal direction.
Bolus-tracking technique was performed 5 seconds after contrast injection, and
serial tracker images were obtained at the level of the ascending aorta. After
the region of interest in the ascending aorta reached the threshold of 150 H,
scanning was started after a 5-second postthreshold delay. For patients who
could hold their breath when instructed, scans were obtained with a
breath-hold. Otherwise, scans were obtained during free breathing under mild
sedation with rectally administered chloral hydrate.
Patients weighing more than 50 kg were given 100 mL of contrast medium
([iohexol], Omnipaque 350, Amersham) and a 30-mL saline chaser. Patients
weighing less than 50 kg were given contrast medium in the dose of 2 mL/kg
body weight and a saline chaser of 0.6 mL/kg body weight. The flow rate was
the contrast volume divided by the summation of scanning time plus 8. A boy
weighing 35 kg, for example, was given 70 mL of contrast medium and a saline
chaser of 21 mL. After the scanning range was planned on the pilot film, the
scanner reported a scanning time of 13 seconds. Thus, the flow rate for both
contrast medium and saline chaser would be 3.3 mL/s.
Cardiac CT Interpretation
A dedicated MDCT workstation (Extended Brilliance Workspace, Philips
Medical Systems) was used for interpretation. All the reconstructed phases
from 0% to 90% of the R-R interval with 10% spacing were loaded. In the most
quiescent phase, the plane was swiveled to the perpendicular axis of the
Amplatzer septal occluder. To facilitate finding the perpendicular plane, we
simply swiveled the plane to cut through the two metallic points on each side
of the device (the microscrew and the left atrial disk center) (Figs.
1A,
1B,
1C,
1D,
1E,
1F and S1G-S1K.). The reviewer
scrolled up and down to comprehensively evaluate the location and shape of the
device. The relations between the device and the adjacent anatomic
structures—superior vena cava, aorta, left atrium, right atrium,
coronary sinus, and inferior vena cava—also were examined. At least two
orthogonal planes were evaluated to complete the interpretation. We recommend
the oblique axial and oblique sagittal planes because it is easier for
beginners to identify the anatomic structures in these planes. Dynamic motion
during the heart cycle also can be evaluated in any plane. This step was
helpful in visualizing flow in the superior and inferior venae cavae, dynamic
coronary sinus compression, and the relation between the mitral valve and
residual defect or shunt.
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Fig. 1A —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. Oblique axial MDCT image in plane perpendicular to
Amplatzer septal occluder shows anatomic features. Two metallic points
(arrows) should appear simultaneously to ensure perpendicularity
between plane and device. After plane is set, scrolling up and down shows
device for comprehensive evaluation. Oblique axial images are useful in
evaluating device and its relation to aorta, mitral valve, tricuspid valve,
and coronary sinus. LA = left atrium, LV = left ventricle, RA = right atrium,
RV = right ventricle.
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Fig. 1B —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. Oblique sagittal MDCT image shows plane perpendicular to
device. Oblique sagittal images are useful for evaluating device and its
relation to superior vena cava (SVC), inferior vena cava (IVC), and coronary
sinus. Device protrusion over superior and inferior portions can be easily
identified. LA = left atrium, RA = right atrium.
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Fig. 1C —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. MDCT in four-chamber view shows dynamic relations between
device and mitral and tricuspid annuli. LA = left atrium, LV = left ventricle,
RA = right atrium, RV = right ventricle.
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Fig. 1D —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. Multiplanar reformation image with plane through two
metallic points (arrow) and coronary sinus shows severely compressed
coronary sinus.
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Fig. 1E —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. Multiplanar reformation image with plane through two
metallic points and superior vena cava shows laminar flow (arrow)
from superior vena cava to right atrium. In most patients with Amplatzer
septal occluder, right atrial disk (arrowheads) protrudes slightly
into superior vena caval to right atrial flow tract, which is normal
condition. In some patients, protrusion is so prominent that normal laminar
flow is interrupted (Fig.
7C).
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Fig. 1F —9-year-old girl with Amplatzer septal occluder (AGA Medical
Corporation) in good position. See also Figs. S1G-S1K, cine loops, in
supplemental data. Global multiplanar reformation image of coronary arteries
shows malignant coronary anomaly. Right coronary artery arises from left sinus
of Valsalva with interarterial course (arrowheads). High-pressure
compression between aorta (Ao) and right ventricular outflow tract (RVOT)
would expose patient to risk of sudden death during vigorous exercise.
Whole-heart approach is important during interpretation because atrial septal
defect can be combined with other congenital cardiac anomaly. AL = anterior
leaflet, CRX = circumflex artery, LAD = left anterior descending coronary
artery, RA = right atrium, RCA = right coronary artery.
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Results
Good Position
In well-selected cases with adequate septal rim and sizing (Fig.
1A,
1B,
1C,
1D,
1E,
1F), the results of ASD closure
were excellent [3] (Figs.
S1G-S1K). In any perpendicular axis, the left atrial disk should be in the
left atrium, and the right atrial disk should be in the right atrium with the
waist of the device stenting the ASD. In the correct position, a properly
sized device is disk shaped rather than mushroom shaped (see section, ASD
Closed with Relatively Large Amplatzer Septal Occluder).
Multiple ASD Managed with Two Amplatzer Septal Occluders
In selected patients with two or more atrial septal defects (Figs.
2A,
2B,
2C, S2D, and S2E), we used two
Amplatzer septal occluders to close all the defects. The several-millimeter
margins between the borders of the two disks and the waist was used to cover
adjacent small defects. Because of acoustic shadowing, it is difficult to use
TTE to examine patients in whom two devices have been inserted. MDCT is used
to evaluate these patients. The perpendicular plane must be used to evaluate
each device.
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Fig. 2A —3-year-old boy after insertion of two Amplatzer septal occluders
(AGA Medical Corporation). MDCT was performed with mild sedation and free
breathing. See also Figs. S2D and S2E, cine loops, in supplemental data.
Oblique axial MDCT image in plane through center of upper and larger Amplatzer
septal occluder shows proper position of device. LA = left atrium, LV = left
ventricle, RA = right atrium, RV = right ventricle.
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Fig. 2B —3-year-old boy after insertion of two Amplatzer septal occluders
(AGA Medical Corporation). MDCT was performed with mild sedation and free
breathing. See also Figs. S2D and S2E, cine loops, in supplemental data.
Oblique axial MDCT image in plane through lower, smaller device shows
suspected device migration with mild compression of coronary sinus. LA = left
atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
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Fig. 2C —3-year-old boy after insertion of two Amplatzer septal occluders
(AGA Medical Corporation). MDCT was performed with mild sedation and free
breathing. See also Figs. S2D and S2E, cine loops, in supplemental data.
Oblique sagittal MDCT image shows two devices in proper position. Both devices
cross border (dashed line) between left atrium (LA) and right atrium
(RA). Device position is difficult to evaluate with transthoracic
echocardiography because of limited acoustic window and severe acoustic
shadow. This case emphasizes need to evaluate Amplatzer septal occluder in
perpendicular plane.
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ASD Closed with Relatively Large Amplatzer Septal Occluder
Sizing of the device refers to the relative size between the occluder and
the defect. Before deployment, repeated sizing with a sizing balloon, sizing
plate, or intracardiac echocardiography was performed to measure the defect.
Thus, in single ASD, even the largest 40-mm Amplatzer septal occluder can be
placed adequately if properly sized
[4] (Figs.
3A,
3B, S3C, and S3D). In patients
with more than one ASD, because the sizes would change with application of
different stenting forces, it was difficult to determine the adequate sizes of
Amplatzer septal occluders. We therefore deployed one occluder on the smaller
ASD and then used a relatively larger occluder to close the larger defect and
clip the small occluder to provide extra stability. A mushroom shape, which
indicated the occluder was larger than the stretched size of the ASD, was
identified (Figs. 4A,
4B,
4C,
4D, S4E, and S4F). Because the
disks do not clip the rim tightly under such conditions, it was important to
evaluate for residual shunt through the waist.
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Fig. 3A —31-year-old woman after insertion of 40-mm Amplatzer septal occluder
(AGA Medical Corporation), which is in good position. See also Figs. S3C and
S3D, cine loops, in supplemental data. Forty-millimeter Amplatzer device is
not yet approved by U.S. Food and Drug Administration. Oblique sagittal MDCT
image shows proper position of device. LA = left atrium, IVC = inferior vena
cava, RA = right atrium.
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Fig. 3B —31-year-old woman after insertion of 40-mm Amplatzer septal occluder
(AGA Medical Corporation), which is in good position. See also Figs. S3C and
S3D, cine loops, in supplemental data. Forty-millimeter Amplatzer device is
not yet approved by U.S. Food and Drug Administration. Four-chamber view MDCT
image shows relation between device and mitral and tricuspid valves
(arrowheads) and space (arrow) between device and mitral
valve. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right
ventricle.
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Fig. 4A —18-year-old woman with incidentally found left ventricular
noncompaction after insertion of two Amplatzer septal occluders (AGA Medical
Corporation), one of which is relatively large. See also Figs. S4E and S4F,
cine loops, in supplemental data. Oblique sagittal MDCT image in plane through
two devices shows tethered waist (arrow) and mushroom shape of larger
device. Larger device was chosen to adequately clip upper smaller device and
provide extra stability. LA = left atrium, RA = right atrium, SVC = superior
vena cava.
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Fig. 4B —18-year-old woman with incidentally found left ventricular
noncompaction after insertion of two Amplatzer septal occluders (AGA Medical
Corporation), one of which is relatively large. See also Figs. S4E and S4F,
cine loops, in supplemental data. Photograph shows disk shape of 20-mm
Amplatzer septal occluder clipping 20-mm defect. Both left and right atrial
disks are flat and in close contact with rim.
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Fig. 4C —18-year-old woman with incidentally found left ventricular
noncompaction after insertion of two Amplatzer septal occluders (AGA Medical
Corporation), one of which is relatively large. See also Figs. S4E and S4F,
cine loops, in supplemental data. Photograph shows 20-mm Amplatzer septal
occluder placed into 6-mm hole, which is too small for device. Mushroom shape
is caused by waist tethering (arrow).
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Fig. 4D —18-year-old woman with incidentally found left ventricular
noncompaction after insertion of two Amplatzer septal occluders (AGA Medical
Corporation), one of which is relatively large. See also Figs. S4E and S4F,
cine loops, in supplemental data. MDCT image of short axis of left ventricle
shows prominent left ventricular trabeculation (black arrows),
prominent noncompaction (NC) layer (long white arrow), and thin
compaction (C) layer (short white arrow). Ratio of noncompaction
layer to compaction layer is greater than 2, which meets criterion for
diagnosis of left ventricular noncompaction. This rare cardiomyopathy is
difficult to recognize even retrospectively on transthoracic echocardiography.
Because disease is inherited, family screening was undertaken and showed same
disorder in patient's 15-year-old brother. LV = left ventricle, RV = right
ventricle.
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Good Position but Residual Shunt
Good position of the occluder but residual shunt is shown in
Figure 5 (also Fig. S5.) Most
ASDs are not circular. They can be oval or irregular in shape
[5]. In some cases, even when
the septal occluder was placed in proper position, the defect still was not
completely closed. In such circumstances, the residual defect was usually out
of the acoustic window of TTE, and the echogenic disk blocked detailed
evaluation. MDCT was useful in the evaluation of these patients. Patients such
as these need close follow-up to determine whether the residual defect is
clinically important. Epithelialization seals the defect in some cases. If
needed, surgical removal of the device with simultaneous closure of the defect
can be considered.
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Fig. 5 —7-year-old boy with minimal residual shunt due to rim deficit after
insertion of Amplatzer septal occluder (AGA Medical Corporation). Oblique
axial MDCT image shows 1-mm residual defect (arrow) near superior
vena cava (SVC). In some patients, focal rim deficit results in residual
defect even with proper position of device. Because of high position and
device blocking, transthoracic echocardiography could not be used to evaluate
residual defect. Because patient's condition was asymptomatic, outpatient
follow-up was suggested because small defect can be sealed during
epithelialization. Ao = aorta, LA = left atrium, LAA = left atrial appendage,
RAA = right atrial appendage, RVOT = right ventricular outflow tract. See also
Fig. S5, cine loop, in supplemental data.
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Mild Protrusion but No Residual Shunt
Mild protrusion of the device with no residual shunt is shown in Figure
6A,
6B (also Figs. S6C-S6E). In
some patients, good position without residual shunt was found immediately
after deployment. With the rim defect and several days of heart beating,
however, sliding can occur owing to inadequate fixing force. In most cases,
the protrusion was minimal, without residual defect or instability. With the
passage of time, epithelialization can cover the protrusion.
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Fig. 6A —34-year-old woman with minimal protrusion due to rim deficit but no
residual shunt after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S6C and S6D, cine loops, in supplemental data.
Oblique sagittal MDCT image shows upper portion of device protruding into
right atrium (RA). Both left and right atrial disks (arrow) are in
right atrium. IVC = inferior vena cava, LA = left atrium, SVC = superior vena
cava.
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Fig. 6B —34-year-old woman with minimal protrusion due to rim deficit but no
residual shunt after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S6C and S6D, cine loops, in supplemental data.
Oblique coronal MDCT image confirms position in another plane. Arrow indicates
protruded upper portion of device. IVC = inferior vena cava, LA = left atrium,
RA = right atrium, SVC = superior vena cava.
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Device Protrusion with Mild Residual Shunt
Device protrusion with mild residual shunt is shown in Figure
7A,
7B,
7C,
7D (also Figs. S7E-S7G).
Because of the inherent curves of the atrial septum and inability to fit the
device in some patients, in combination with rim deficit and vigorous cardiac
motion, intracardiac echocardiography immediately after the procedure might
have shown no residual defect, but protrusion and residual shunt developed
later. The protrusion usually was over the region of the rim deficit.
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Fig. 7A —8-year-old girl with minimal residual shunt between left atrium and
inferior vena cava after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S7E-S7G, cine loops, in supplemental data.
Oblique sagittal MDCT image shows residual shunt from left atrium (LA) to
inferior vena cava (arrow). Shunts appear as radiopaque jet
projecting from defect to right side of heart. RA = right atrium.
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Fig. 7B —8-year-old girl with minimal residual shunt between left atrium and
inferior vena cava after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S7E-S7G, cine loops, in supplemental data. MDCT
image shows protrusion and residual shunt related to different inherent curves
of atrial septum (black line) and device (white line). LA =
left atrium, RA = right atrium, RAA = right atrial appendage, SVC = superior
vena cava.
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Fig. 7C —8-year-old girl with minimal residual shunt between left atrium and
inferior vena cava after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S7E-S7G, cine loops, in supplemental data.
Oblique sagittal MDCT image in diastolic phase shows absence of shunt
(arrow). Because of pressure change during heart cycle and
check-valve effect of device, left-to-right shunt was present only in systolic
phase. Because of low location and blocking by device, residual shunt was
missed on routine follow-up echocardiography.
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Fig. 7D —8-year-old girl with minimal residual shunt between left atrium and
inferior vena cava after insertion of Amplatzer septal occluder (AGA Medical
Corporation). See also Figs. S7E-S7G, cine loops, in supplemental data.
Oblique sagittal MDCT image in plane through device and superior vena cava
shows upper portion of right atrial disk (arrowheads) protruding into
superior vena caval to right atrial flow tract, causing turbulent flow
(arrows).
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Marked Device Protrusion with Large Residual Shunt
Marked device protrusion with large residual shunt is shown in Figure
8A,
8B,
8C,
8D,
8E,
8F,
8G,
8H (also Figs. S8H-S8J). In
some cases, probably because of rim deficit or poor fit between the device and
the atrial septum, a small residual shunt appeared on intracardiac
echocardiography immediately after the procedure. Patients with these findings
need close follow-up to assess whether the shunt seals by epithelialization or
enlargement. There are only limited reports in the literature about device
dislocation and migration, and the incidence is considered low. Because of
instability, surgical removal with defect closure is suggested to prevent
distal migration [6].
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Fig. 8A —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Lateral chest radiographs show marked device
protrusion in patient (A) and normal position of Amplatzer septal
occluder in different patient of same age (B). Occluder in good
position is in vertical orientation, which represents orientation of atrial
septum. If there is marked protrusion into right atrium, marked anterior
tilting with nearly horizontal orientation is present.
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Fig. 8B —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Lateral chest radiographs show marked device
protrusion in patient (A) and normal position of Amplatzer septal
occluder in different patient of same age (B). Occluder in good
position is in vertical orientation, which represents orientation of atrial
septum. If there is marked protrusion into right atrium, marked anterior
tilting with nearly horizontal orientation is present.
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Fig. 8C —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Oblique sagittal MDCT image shows marked
protrusion of upper portion of both left and right atrial disks
(arrowheads) in right atrium. Residual defect (arrow) also
is evident. LA = left atrium, RA = right atrium.
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Fig. 8D —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Systolic (D) and diastolic (E)
MDCT images of same section show waving of atrial septum (arrows).
Intracardiac sonogram immediately after deployment of device showed good
position of device with only minimal shunting. After 1 week, marked protrusion
was found on chest radiograph and transthoracic echocardiogram. Cause of
migration was not clear but was considered to be related to rim deficit and
redundant and waving atrial septum.
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Fig. 8E —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Systolic (D) and diastolic (E)
MDCT images of same section show waving of atrial septum (arrows).
Intracardiac sonogram immediately after deployment of device showed good
position of device with only minimal shunting. After 1 week, marked protrusion
was found on chest radiograph and transthoracic echocardiogram. Cause of
migration was not clear but was considered to be related to rim deficit and
redundant and waving atrial septum.
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Fig. 8F —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Virtual angioscopic image from workstation
shows relations between device and septum. Residual defect and extent of
protrusion are evident. ASO = Amplatzer septal occluder, LSPV = left superior
pulmonary vein, RIPV = right inferior pulmonary vein, RSPV = right superior
pulmonary vein.
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Fig. 8G —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Surgical photograph shows protruding device.
To prevent further migration, surgical removal of device with concomitant
atrial septal defect closure was performed. After incision of right atrium,
migrated upper portion (arrowheads) and normally positioned lower
portion (arrow) clipping lower atrial septum were identified. Forceps
indicates protruded upper portion of device in right atrium.
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Fig. 8H —43-year-old man with marked device protrusion after insertion of
Amplatzer septal occluder (AGA Medical Corporation). See also Figs. S8H-S8J,
cine loops, in supplemental data. Virtual angioscopic image viewed from right
atrium shows findings identical to surgical findings, that is, migrated upper
portion (arrowheads) and normally positioned lower portion
(arrow) clipping lower atrial septum.
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Device Compression of Coronary Sinus
Compression of the coronary sinus was found in cases of rim deficit near
the coronary sinus (Figs. 1D
and S1J.) In general, however, the coronary sinus had a large lumen
(approximately 1 cm) and the Amplatzer septal occluder moved during the heart
cycle, so the compression was usually dynamic and seldom caused occlusion.
Thus, the condition was usually asymptomatic, and no further intervention was
required.
Incidentally Found Cardiac Lesions
Because of the excellent spatial resolution of MDCT, we were able to
evaluate cardiac abnormalities while assessing the results of treatment with
the Amplatzer septal occluder. These lesions, which were not seen on
echocardiography, may further explain the clinical course and symptoms.
Radiologists evaluating MDCT images after insertion of the septal occluder
should evaluate the entire heart, including the coronary arteries (Figs.
1F and
9B), myocardium
(Fig. 4C), and other
cardiovascular structures, such as the left superior vena cava (Figs. S1, S4,
and S9).
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Fig. 9B —35-year-old man with incidental finding of left main coronary artery
compressed by right pulmonary artery during evaluation after insertion of
Amplatzer septal occluder (AGA Medical Corporation). Patient had experienced
long-term chest tightness and was found to have atrial septal defect, which
was closed with Amplatzer septal occluder. Chest tightness did not subside
after procedure. Because of unusual clinical course, MDCT was performed for
further device evaluation. See also Fig. S9C, cine loop, in supplemental data.
Oblique coronal MDCT image in section through left main coronary artery (LM)
shows dilated right pulmonary artery (RPA) compressing proximal portion of
left main coronary artery with 90% diameter stenosis. Because pulmonary artery
diameter and pressure were expected to decrease after closure of atrial septal
defect, patient was discharged with oral ß-blocker and advice to avoid
vigorous exercise. Symptoms subsided gradually within 6 months. This case
emphasizes importance of whole-heart evaluation, especially when clinical
course cannot be explained. Ao = aorta, ASO = Amplatzer septal occluder, CPA =
central pulmonary artery, LV = left ventricle, RV = right ventricle.
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Discussion
MDCT was feasible for evaluating Amplatzer septal occluders. The metallic
component of the occluder, which is a major problem for MRI and
echocardiography, does not impair the diagnostic quality of MDCT scans.
Because MDCT can depict any plane retrospectively owing to its volume data
acquisition capability, many residual defects, shunts, and protrusions not
seen on TTE can be identified. If symptoms are present that cannot be
explained by the TTE findings or if TTE cannot be used with confidence to
evaluate the device, MDCT is a good choice for further evaluation.
In addition to MDCT after TTE, intracardiac sonography and transesophageal
echocardiography can be used to evaluate septal occluding devices. These
techniques are invasive, however, and necessitate sedation or general
anesthesia, which cannot be performed on an outpatient basis. All patients
except those with contraindications to radiation exposure or injection of
contrast medium can be referred for MDCT. Because of safety considerations,
artifacts, and limited spatial resolution of MRI, only animal studies of this
technique have been conducted
[7].
The main limitation of MDCT is the inherent radiation. Women of
child-bearing age must be confirmed not to be pregnant. The general pediatric
population also is at risk. Thus, MDCT is not intended to replace TTE as the
routine primary survey technique. In clinical practice, patients should always
be evaluated by TTE before referral for MDCT. Meticulous radiation control
also is needed. We suggest weight-based current selection to avoid excessive
radiation of small children. Another effective way to reduce radiation
exposure is online ECG tube current modulation, as with ECG pulsing or
DoseRight Cardiac (Philips Medical Systems). We did not use this technique
because of possible impairment of image quality during early diastole, a phase
that often is crucial in a child's fast heart rate.
In anatomic regions that cannot be confidently imaged with TTE, MDCT has
powerful capability in evaluation of Amplatzer septal occluders for
protrusion, migration, and residual shunt. Radiologists should be familiar
with the imaging protocol and image interpretation to provide optimum patient
care.
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Fig. 9A —35-year-old man with incidental finding of left main coronary artery
compressed by right pulmonary artery during evaluation after insertion of
Amplatzer septal occluder (AGA Medical Corporation). Patient had experienced
long-term chest tightness and was found to have atrial septal defect, which
was closed with Amplatzer septal occluder. Chest tightness did not subside
after procedure. Because of unusual clinical course, MDCT was performed for
further device evaluation. See also Fig. S9C, cine loop, in supplemental data.
Oblique sagittal MDCT image shows good device position. IVC = inferior vena
cava, LA = left atrium, RA = right atrium, SVC = superior vena cava.
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References
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Abstract
Introduction
