Incremental value of systematic follow-up with CT after left atrial appendage occluder device implantation

Atrial fibrillation can result in thrombus formation in the left atrial
appendage, possibly resulting in a cerebrovascular accident (CVA). The
antithrombotic treatment of atrial fibrillation includes anticoagulants in
patients with a CHA2DS2-VASc score above one.1 Recently left atrial appendage
occlusion (LAAO) devices have been introduced for patients who experience a CVA
under anticoagulant treatment or with a contra-indication for anticoagulant
medication. In the PROTECT-AF study 707 patients with non-valvular atrial
fibrillation and at least one of the following risk factors: age >=75 years,
hypertension, diabetes mellitus, heart failure, prior stroke, transient
cerebral ischemic attack, or systemic thromboembolism were included. Included
patients were randomized for LAAO device implantation or continuation of
warfarin treatment. The LAAO group showed non-inferiority for thromboembolic
complications. The majority of events in the LAAO implantation group were
related to the implantation procedure.2 The 2012 ESC guidelines for atrium
fibrillation provide a moderate recommendation (Class IIb level B) for LAAO
device treatment in patients with contra-indications for anticoagulants.

In our institution approximately twenty patients are annually accepted for LAAO
implantation. Following the protocol used in the PROTECT-AF study patients
continue with warfarin (acenocoumarol) and aspirin for 45 days after
implantation. After 45 days a trans esophageal echocardiography (TEE) is
performed. When the peri-device flow is absent or smaller in diameter than 5mm
the warfarin is discontinued and clopidogrel is started. After 6 months the
clopidogrel is also discontinued and only aspirin is continued indefinitely. In
case of a peri-device flow larger than 5mm the warfarin is continued at the 45
day interval. Periodically the peri-device flow will be measured again. If it
becomes smaller than 5mm the warfarin can be stopped, and clopidogrel will be
added following the protocol for peri-device flow below 5 mm.
Peri-device flow is defined as blood flow next to the LAAO, by using multiple
angulations the maximal diameter is measured. Using CT contrast enhancement on
the occluded (distal) side on the LAAO device will be measured. The contrast
enhancement distal of the LAAO device will be compared with the peri-device
flow measured with TEE. The ostium of the LAA is usually oval shaped. The LAAO
occluder has a circular shape. This can result in incomplete coverage at the
oval sides causing peri-device flow.
The PROTECT-AF study showed that in a substantial number of the patients (41%)
peri-device flow is present, and in 13% of the patients warfarin was continued
at the 45 days interval.3
This study aims to prove CT is a reliable alternative for TEE to detect flow
distal to the LAAO device. Currently one study has shown good results when
comparing CT follow-up after LAAO device implantation with TEE, although this
study included a limited number of patients and only patients implanted with an
AMPLATZER type device.4 The type of device implanted is at the treating
physician discretion, from current hospital records we expect the large
majority of our cases to have been implanted a WATCHMAN type device.
If results of the CT scan post implantation are favorable a shift from TEE
towards CT examinations might take place. This would save the patient an
uncomfortable TEE procedure.

Primary Objective:
• Investigate if CT is a reliable modality to detect blood flow distal to the
LAAO device validated by TEE.

Secondary Objective(s):
• Evaluate the reproducibility of position and blood flow measurements: inter
and intra observer variance, CT compared with TEE.

• Determine the optimal device position and size, based on pre-implantation
anatomical CT data. Measurements of the LAA shape, ostium, depth and
trabeculations in relation to the LAAO device landing position. When describing
the ostium diameters specific attention can be placed on the oval shape as the
ability of the device to change it from a circular to an oval shape is limited.

• Compare CT findings with clinical follow-up with specific interest for
thromboembolic complications. Investigate if these can be related to suboptimal
device position, trabeculations at the device landing zone, or contrast
enhancement distal to the device.

• Size of the LAA distal to the device can be measured and compared to the LAA
size as measured before implantation. Possibly allowing for volumetric
measurements of thrombus and to determine the ratio of contrast and thrombus
distal to the LAAO device.

The study is a single-center observational study.

The CT measurements will be compared with the standard of care TEE images. This
study is performed in close collaboration with the cardiologists involved in
the LAAO device implantation. We aim to include approximately 80% of the
patients accepted for the LAAO device implantation. We expect approximately
thirty patients will be accepted annually for LAAO device implantation in our
center. Patients will be informed about the study at the outpatient patient
clinic. If the patient is accepted for LAAO device implantation the
cardiologist will ask the patients to consider participation in the study and
provide the study information documentation. If the patient is positive towards
participation a follow-up consult with a research fellow (MD) will be made
where the study design, patients risks, and population benefits are discussed
in more detail.
The patients included will undergo a CT scan at the 45 days interval in
addition to the TEE. The study will run until 41 patients are included. With an
inclusion percentage of 80% we suspect to completed inclusion within 2 years.

Only patients who are accepted for LAAO device implantation will be included.
Several radiation reduction techniques will be applied to reduce the radiation
exposure for the study subjects. E.g. optimizing the selected scan mode
prospective EKG triggered acquisition, and patient specific tube current and
voltage modulation. The radiation dose from the complete CT scan will be
approximately 3-5 mSv including both scans. The radiation dose is approximately
double the annual radiation dosage from background radiation.5 The scan
requires the injection of an iodine contrast agent. Patients known with
contrast allergy will be excluded from the study. To minimize the risk of renal
injury, patients with an impaired renal function (serum creatinine>120 *µmol/l
or GFR<60 ml/min) will be excluded from the study.
Benefits:
There are no benefits for the individual subject.
Benefits to the population:
The study will help in creating protocols and measurement methods to follow-up
patients after LAAO device implantation. Possible causing a shift from an
inconvenient TEE to a CT scan.