DOI:10.2214/AJR.04.1875
AJR 2006; 186:361-364
© American Roentgen Ray Society
Percutaneous Left Atrial Appendage Transcatheter Occlusion (PLAATO): Planning and Follow-Up Using Contrast-Enhanced MRI
Oliver K. Mohrs1,2,
Rainer Schraeder2,
Steffen E. Petersen3,
Detlef Scherer1,
Bernd Nowak1,
Hans-Ulrich Kauczor2 and
Thomas Voigtlaender1
1 Department of MRI, Cardiovascular Center Bethanien (CCB), Im Pruefling 23,
D-60389 Frankfurt/Main, Germany.
2 German Cancer Research Center DKFZ, Heidelberg, Germany.
3 University of Oxford, OCMR, John Radcliffe Hospital, Oxford, United
Kingdom.
Received December 9, 2004;
accepted after revision January 12, 2005.
Address correspondence to O. K. Mohrs
(o.mohrs{at}gmx.de).
Keywords: cardiac imaging • cardiovascular disease • dynamic MRI • implantable devices • MRI
Introduction
Left atrial thrombus is a frequent cause of cerebral stroke or peripheral
embolism in patients with atrial fibrillation. Anticoagulation is required to
prevent further cerebral events
[1]. The main location for left
atrial thrombus formation is the left atrial appendage, possibly because of
the phenomenon of atrial stunning
[2]. Therefore, in patients
with contraindications to warfarin treatment, occlusion of the left atrial
appendage could be a potential alternative strategy for prophylaxis of
embolism. In comparison with surgical amputation, the percutaneous left atrial
appendage transcatheter occlusion (PLAATO) is a minimally invasive technique
[3].
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Fig. 1A —Images show percutaneous left atrial appendage transcatheter
occlusion (PLAATO) device (PLAATO, ev3). Photograph shows device, which has a
nitinol self-expanding framework and an expandable polytetrafluoroethylene
cover. Faced to apex of left atrial appendage cover is opened for filling of
blood and a later thrombosis inside the device.
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Fig. 1B —Images show percutaneous left atrial appendage transcatheter
occlusion (PLAATO) device (PLAATO, ev3). MR image obtained for in vitro test
shows only low artifacts of nitinol framework itself. Bright signal of
contrast agent filled in tube A (arrow) is clearly visible between
frames and inside device. B = surrounding tube filled with saline solution and
small amount of contrast agent.
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Currently, after the PLAATO procedure, chest radiography is performed to
confirm the correct placement of the occluder and transesophageal
echocardiography is performed to evaluate possible thrombotic appositions on
the device. To date, it has been impossible to assess the degree of residual
left atrial appendage perfusion, which would indicate the degree of
noncoverage of the atrial-facing surface of the device with
neoendothelial-like cells
[4].
In our report, we present the potential of contrast-enhanced MRI, before
and after PLAATO, to assess left atrial appendage perfusion in a patient.
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Fig. 2 —71-year-old man with persisting nonrheumatic atrial fibrillation who
suffered from thromboembolic events three times before and twice during
warfarin therapy and was referred for percutaneous left atrial appendage
transcatheter occlusion (PLAATO). Before PLAATO, contrast-enhanced MRI in
saturation recovery true FISP (fast imaging with steady-state free precession)
sequence (TE, 2.7; inversion time, 217 msec; flip angle, 50°; temporal
resolution, 832 msec; voxel size, 1.8 x 1.4 x 6.5 mm3)
shows complete perfusion of left atrial appendage (arrow) before
occlusion. Patient was administered 10 mL gadopentetate dimeglumine followed
by 30 mL of saline solution at rate of 6 mL/sec. PT = pulmonary trunk.
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Case Report
A 71-year-old man with persisting nonrheumatic atrial fibrillation suffered
from thromboembolic events three times before and twice during warfarin
therapy and was referred to our center for PLAATO. For optimal placement of
the delivery catheter and special device (PLAATO device, ev3) (Figs.
1A and
1B), the anatomy and size of
the left atrial appendage were assessed. Additionally, thrombus was excluded
by means of transesophageal echocardiography and contrast-enhanced dynamic
MRI.
The MR examinations were performed on a 1.5-T MR scanner (Magnetom Sonata
Maestro Class, Siemens Medical Solutions). For signal detection the
combination of a six-channel body phased-array coil and a two-channel spine
phased-array coil was used.
An ECG-gated segmented true fast imaging with steady-state free precession
(FISP) cine sequence (TR/TE, 2.7/1.2; temporal resolution, 34 msec; voxel
size, 1.7 x 1.3 x 6.0 mm3) was used to determine left
atrial appendage anatomy. Contrast-enhanced MRI was then performed in two
views aligned through the long and short axes of the left atrial appendage.
For this, 40 consecutive images were acquired using a contrast-enhanced 2D
perfusion study (saturation recovery true FISP sequence: TE, 2.7 msec;
inversion time, 217 msec; flip angle, 50°; 2 slices simultaneously in
different angulations; temporal resolution, 832 msec; voxel size, 1.8 x
1.4 x 6.5 mm3) during the administration of a bolus of 10 mL
of gadopentetate dimeglumine (Magnevist, Schering) followed by 30 mL of
saline, both injected into an antecubital vein at 6 mL/sec.
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Fig. 3A —Follow-up contrast-enhanced MRI at 12 weeks after percutaneous left
atrial appendage transcatheter occlusion (PLAATO) shows temporal sequence of
contrast-enhanced perfusion imaging. Contrast enhancement is seen only in
pulmonary trunk whereas apex of left artial appendage (arrow) is not
enhanced. Typical signal loss at framework of device (dotted arrow)
is noted. PT = pulmonary trunk, LA = left atrium, A = aorta ascendens.
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Fig. 3B —Follow-up contrast-enhanced MRI at 12 weeks after percutaneous left
atrial appendage transcatheter occlusion (PLAATO) shows temporal sequence of
contrast-enhanced perfusion imaging. Contrast enhancement is seen in left
atrium but not inside device or at apex of left atrial appendage.
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Fig. 3C —Follow-up contrast-enhanced MRI at 12 weeks after percutaneous left
atrial appendage transcatheter occlusion (PLAATO) shows temporal sequence of
contrast-enhanced perfusion imaging. Simultaneous enhancement of aorta and
slight enhancement at apex of left atrial appendage beyond unenhanced device
are seen.
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Fig. 3D —Follow-up contrast-enhanced MRI at 12 weeks after percutaneous left
atrial appendage transcatheter occlusion (PLAATO) shows temporal sequence of
contrast-enhanced perfusion imaging. Complete enhancement of apex of left
atrial appendage (arrow) is seen, but there is still no significant
enhancement of device. Enhancement beyond device at this time represents slow
wash-in and washout due to small residual perfusion.
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Figure 2 shows the anatomy
and sizing (especially diameter of orifice and long-axis diameter) of the left
atrial appendage. A thrombus in the left atrial appendage could be excluded
(movie 1, available online at
www.ajronline.org).
These findings were confirmed by transesophageal echocardiography before and
left atrial appendage angiography during transcatheter closure.
Contrast-enhanced MRI was repeated 12 weeks after PLAATO to assess correct
placement of the device and to evaluate possible residual perfusion of the
left atrial appendage. Thrombotic appositions at the atrial-facing surface of
the device were excluded by MRI and confirmed by transesophageal
echocardiography. At the apex of the left atrial appendage beyond the device
contrast-enhanced MR image showed slight contrast enhancement (Figs.
3A,
3B,
3C, and
3D and movie 2, available
online at
www.ajronline.org).
This finding could not be assessed by means of flow signals beyond the device
using transesophageal echocardiography. Because of this finding, the patient
received further oral anticoagulation.
Follow-up contrast-enhanced MRI was performed 20 weeks after PLAATO. This
time, only a minimal enhancement in the left atrial appendage could be
detected (Fig. 4 and movie 3,
available online at
www.ajronline.org),
which related to a reduction of the residual perfusion compared with the
follow-up study 12 weeks after device implantation.
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Fig. 4 —Follow-up MRI 20 weeks after percutaneous left atrial appendage
transcatheter occlusion. Compared with previous examination (Figs.
3A,
3B,
3C, and
3D), residual perfusion
decreased concerning area and intensity of enhancement. Only circumscribed
enhancement was seen at appendage-faced border of device (arrow),
whereas apex of left atrial appendage was not perfused.
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Discussion
To facilitate PLAATO in selected patients with atrial fibrillation and
recurrent embolic events, the evaluation of left atrial appendage anatomy and
exclusion of thrombus before device implantation and the confirmation of
correct device placement and assessment of residual perfusion after
transcatheter occlusion are important. To the best of our knowledge, this case
report shows for the first time the successful application of
contrast-enhanced MRI to answer these questions.
Atrial fibrillation is the most common cardiac arrhythmia. Due to the risk
of thromboembolism many patients with atrial fibrillation are treated with
anticoagulants. Longterm therapy with warfarin is associated with an increased
risk of minor (5-10% per year) and major (1-2% per year) hemorrhagic
complications [5]. This forms
the rationale for alternative approaches, such as PLAATO. The principle of
this technique necessitates correct placement, a functioning clotting cascade,
and complete coverage with neoendothelial-like cells at the atrial-facing
surface of the device. Recent studies have shown the feasibility of PLAATO in
patients with atrial fibrillation to prevent further embolism
[4].
Currently, chest radiography and echocardiography are used to verify
correct placement of the device and to exclude thrombotic appositions in
patients. Only a contrast fluoroscopic "appendogram" could prove
the residual perfusion of the left atrial appendage indicating coagulation of
the device and complete coverage with neoendothelial-like cells. The major
drawback of this method is its invasiveness. Therefore a noninvasive imaging
method integrating assessment of anatomy and residual perfusion would be
advantageous.
In a recent animal study the anatomic and histologic inspection showed that
the atrial-facing surface of the occlusion membrane is completely covered with
a smooth intact neointimal layer 3 months after device implantation
[3].
In safety studies, a time interval of 6 weeks is recommended between
implantation and MRI examination for intracardiac devices to ensure that the
device is fixed to the endocardial tissue
[6]. Also, our in vitro tests
(unpublished data) showed that imaging these nitinol and expandable
polytetrafluoroethylene devices causes minimal artifacts.
Contrast-enhanced MRI revealed residual perfusion of the left atrial
appendage 12 weeks after device implantation. This suggested residual
perfusion was most likely due to incomplete coverage with neoendothelial-like
cells at the atrial-facing surface of the device. The residual perfusion
decreased when assessed again 20 weeks postprocedure indicating further
coverage of the device, leaving only a minimal gap between the left atrium and
left atrial appendage.
We postulate that the different grades of residual perfusion indicate the
steps of coverage with neoendothelial-like cells at the atrial-facing surface
of the device. Residual perfusion could be a source of thromboemboli and these
patients should be considered for anticoagulation.
In the future, in patients with PLAATO, contrast-enhanced MRI could replace
preprocedure transesophageal echocardiography and provide a noninvasive way to
exclude or stage a residual leak
[4,
7]. However, despite our
encouraging initial experience using contrast-enhanced MRI, this warrants
further investigation regarding its predictive value and impact on treatment
strategies.
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