Elsevier

Heart Rhythm

Volume 3, Issue 11, November 2006, Pages 1313-1318
Heart Rhythm

Original-clinical
Analysis of the left atrial appendage by magnetic resonance angiography in patients with atrial fibrillation

https://doi.org/10.1016/j.hrthm.2006.07.022Get rights and content

Background

Recent interest has focused on the left atrial appendage (LAA) in the setting of atrial fibrillation as a potential source of thromboembolism and stroke, which may be amenable to permanent occlusion by a variety of investigational catheter-delivered devices. Precise anatomic characterization of the LAA is necessary to determine the suitability of a patient for device placement and for device selection and sizing.

Objectives

The purpose of this study was to perform detailed three-dimensional characterization of LAA size and geometry by magnetic resonance angiography.

Methods

Fifty patients with chronic atrial fibrillation undergoing cardiac magnetic resonance angiography in preparation for catheter ablation of atrial fibrillation were analyzed for LAA volume, neck size, depth, and overall geometry.

Results

The average LAA volume was 17.3 ± 6.7 mL, with a depth of 26.6 ± 4.9 mm and a “neck” diameter of 20.0 ± 5.3 mm × 14.1 ± 4.7 mm. The average number of LAA lobes was 1.4 ± 0.7 (range 1–4). Substantial interpatient variability was present in the relative dimensions and morphology of the LAA. There was a significant correlation between left atrial size and LAA neck dimensions.

Conclusion

There is significant heterogeneity in LAA size and dimensions among patients with atrial fibrillation. Device occlusion of the LAA may require devices that are available in multiple sizes/shapes or that can adapt to this heterogeneity.

Introduction

Detailed analysis of cardiac anatomy based on high-resolution imaging studies is increasingly utilized by cardiologists and cardiac electrophysiologists to guide interventional procedures. Precise characterization of left atrial (LA) structures, particularly the pulmonary veins, has been important in the evolution of the ablation procedure for atrial fibrillation (AF).1, 2 Until recently, the left atrial appendage (LAA) has been considered primarily as a potential source of thromboembolus and stroke. For this reason, imaging of the LAA has primarily been directed at the presence of thrombus, spontaneous echo contrast, and other risk factors for thromboembolism by echocardiography,3, 4 with less focus on detailed LAA dimensions and geometry.

The recent development of percutaneous, catheter-delivered LAA closure devices may allow for the direct prevention of strokes associated with LAA thromboembolism.5, 6 In order for such a device to fully occlude and be safely retained within the LAA, either it must be a reasonable size and shape to match a particular patient’s LAA anatomy, or it must be able to adapt to a variety of LAA dimensions. For this reason, a detailed description of the range of LAA sizes and anatomic variations present in patients with AF is important.

The aim of this study was to analyze the three-dimensional geometry and dimensions of the LAA in a series of patients with chronic AF by magnetic resonance angiography (MRA), with a focus on measurements likely to be particularly important with regard to the selection and sizing of occlusion devices. These dimensions include LAA neck diameter (short and long axis), depth, volume, and number of lobes. In addition, a comparison was made between various patient characteristics and LAA dimensions.

Section snippets

Study population

The study population consists of 50 consecutive patients with chronic AF undergoing gadolinium-enhanced cardiac MRA in preparation for catheter ablation procedures for AF with adequate imaging of the entire LAA. MRA was performed in all patients prior to the ablation procedure. AF duration was measured from the first documented episode of AF until the MRA was performed. Body surface area was calculated based on the Mosteller formula. Patient characteristics are given in Table 1.

Cardiac MRA

MRA was

LAA dimensions and neck

Data for LAA volumetric analysis were available for all 50 patients examined. The LAA is composed of an LAA body that is separated from the LA by an oval-shaped “neck.” The long axis of the LAA neck is generally in the superoinferior orientation, and the short axis is directly perpendicular to the long axis within the two-dimensional plane of the LAA neck. Delineation of the LAA neck (with short- and long-axis measurements of the neck) and the LAA depth are shown in Figure 1. The LAA

Discussion

This study has resulted in several important findings. First, there is substantial interpatient variability in the major dimensions of the LAA in a series of typical patients with chronic AF, including variability in LAA volume, neck dimensions, and depth. Second, there are large differences in LAA neck shape and in the ratio of neck size to depth among these patients. Third, there is a significant correlation between LA size and LAA neck dimensions in both the short and long axis. Fourth,

Conclusion

There are significant differences in LAA size and geometry with regard to LAA volume, neck dimensions, depth, and morphology among the patients in this study. Given the increasing interest in device occlusion of the LAA, 3D MRA analysis of LAA structure may prove useful for guiding the appropriate selection and sizing of occlusion devices in the preprocedural setting.

References (14)

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Cited by (0)

1

Dr. Heist is a speaker for Guidant Corp. and receives research support from Guidant Corp. and St. Jude Medical.

2

Dr. Ruskin is a consultant for Medtronic.

3

Dr. Mansour is a consultant for Biosense-Webster.

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