Page 21 - Journal of Structural Heart Disease Volume 5, Issue 5

Original Scientific Article
214
Conclusions: Dimensions of the left atrial appendage ostium vary significantly within different time points in cardiac cycle. These changes are more pronounced in patients in sinus rhythm compared to patients in atrial fibrillation which might impact sizing if CT is used for procedural planning prior to interventional closure of the LAA. According to our data, to identify maximal LAA dimensions, CT imaging for the purpose of LAA oc- clusion should be targeted in atrial diastole (40-50% of the peak R-wave to R-wave).
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Key Words
LAA • Closure • Sizing • CT
Introduction
The association between atrial fibrillation and isch- emic cerebrovascular events has been established in numerous prospective studies [1]. Oral anticoag- ulation is currently the therapy of choice to prevent thromboembolic complications in patients with atrial fibrillation [2]. For patients at high risk for bleeding on anticoagulation therapy, percutaneous mechani- cal occlusion of the left atrial appendage (LAA) has emerged as an effective approach for stroke preven- tion [1]. Correct sizing is crucial for successful and safe implantation of the LAA occluder as well as for achieving desired outcomes following interventional closure. Clinically significant complications, including hemodynamically significant pericardial effusion or procedure-related stroke, are reported in up to 4% of cases [3]. Device sizing prior to left atrial appendage (LAA) closure is currently primarily based on transe- sophageal echocardiographic as well as invasive an- giographic measurements, and can be challenging due to the complex and highly variable anatomy of the LAA. Moreover, apart from the complexity of the left atrial appendage anatomy, the LAA has the ability to contract and the dimensions of the LAA-ostium can change variably during the cardiac cycle leading to differences in sizing strategies. CT is a 3-dimensional imaging modality that is increasingly being used for planning structural heart disease interventions [4-11]. Next to its high and isotropic spatial resolution, CT has the advantage of allowing imaging throughout the entire cardiac cycle in arbitrary orientations.
Using multiphase computed tomography, we assessed the variability of the LAA dimensions in patients with sinus rhythm and atrial fibrillation throughout the cardiac cycle.
Material and Methods
Study design and patient population
This is a single center, retrospective study. Consec- utive CT data sets of 101 patients referred for assess- ment prior to or following transcatheter aortic valve replacement were included in this analysis.
DSCT data acquisition and image reconstruction
CT data sets were acquired with a third genera- tion dual source CT system (Somatom Force, Siemens Healthineers, Forchheim, Germany) using spiral ac- quisition with retrospectively ECG-gated reconstruc- tion, with a scan range extending from the pulmonary artery bifurcation to the caudal aspect of the heart. Scan parameters were as follows: tube voltage 100 kV, tube current time product 500 mAs, collimation 2x192x0.6 mm and rotation time 250ms. ECG dose modulation was used with full radiation exposure be- tween 10-70% of the R-wave to R-wave interval and a dose reduction to 20% outside this window. To assess contrast agent transit time, 10ml of contrast agent (Ultravist 370®, Bayer vital, Leverkusen, Germany) was used. For CT angiography, 50 ml at a flow rate of 5ml/ sec, followed by a 50 ml saline chaser at the same flow rate was injected.
For each patient, a multiphase reconstruction in 10% increments of the cardiac cycle was rendered us- ing a small field of view data set to allow for 4-dimen- sional assessment of the left atrial appendage. All reconstructions were rendered using a medium soft convolution kernel (Siemens Bv40) with a slice thick- ness of 0.75 mm and slice increment of 0.5 mm and iterative reconstruction (Admire®, Siemens Health- ineers, Forchheim, Germany) at a strength level of 2.
CT analysis of left atrial appendage
For primary analysis, multiphase reconstructions were transferred to a dedicated workstation (Ziosta- tion2, Ziosoft Inc., Tokyo, Japan). The plane of the left atrial appendage ostium was defined as a plane connecting the upper left pulmonary vein superi-
Journal of Structural Heart Disease, October 2019
Volume 5, Issue 5:213-220