Use of Cardiac Computed Tomography and Magnetic Resonance Imaging in Case Management of Atrial Fibrillation with Catheter Ablation

Abstract

Atrial fibrillation (AF) is the most common arrhythmia associated with the risk of morbidity and mortality in clinical patients. AF is considered as an arrhythmia type that develops and progresses through close connection with cardiac structural arrhythmogenic substrates. Since the introduction of catheter ablation-mediated electrical isolation of arrhythmogenic substrates, cardiac imaging indicates improved treatment outcome and prognosis with appropriate candidate selection, ablation catheter guidance, and post-ablation follow-up. Currently, cardiac computed tomography (CCT) and cardiovascular magnetic resonance (CMR) imaging are essential in the case management of AF at both pre-and post-procedural stages of catheter ablation. In this review, we discuss the roles and technical considerations of CCT and CMR imaging in the management of patients with AF undergoing catheter ablation.

Keywords: Arrhythmia; Atrial fibrillation; Catheter ablation; Computed tomography; Magnetic resonance imaging.

Fig. 1. Function of LA during normal sinus rhythm and during AF.

In normal sinus rhythm, LA function consists of 1) LA reservoir function at LV systole, 2) LA conduit function during early LV diastole, and 3) LA pump function at late LV diastole. In contrast to sinus rhythm, AF results in rapid and inconsistent heart motion, which may be associated with blurring heart contours on cardiac images. AF = atrial fibrillation, LA = left atrium, LV = left ventricle

Fig. 2. Evaluation of LA volume by 3D techniques of CMR imaging.

Transverse (A) and coronal (B) reformatting of CMR images helps determination of LA chamber areas. Sum of LA chamber areas (green) on thin slice CMR images (C) can be considered as measurement of actual LA volume. PVs and LAA are usually excluded in LA volume measurement using 3D LA model. CMR = cardiovascular magnetic resonance, LAA = left atrial appendage, LSPV = left superior pulmonary vein, PVs = pulmonary veins, RIPV = right inferior pulmonary vein, RSPV = right superior pulmonary vein, 3D = three-dimensional

Fig. 3. LA fibrosis determined with 3D LGE-CMR imaging.

3D LGE-CMR image (A) with excellent spatial resolution describes thin LA wall and hyperenhancement areas (arrows) in detail. Segmentation of thin LA wall with slice thickness of < 2 mm (B, C) can reconstruct 3D LA models (D–F) which show tissue composition of LA wall in basis of signal intensity of LGE (arrows, yellow foci). LGE = late-gadolinium enhancement, LIPV = left inferior pulmonary vein

Fig. 4. Evaluation of LAA function by CMR imaging.

VENC CMR imaging can quantify blood flow through LAA ostium. Mechanically, active emptying of LAA can be represented mechanically by active contraction of LAA. It can be measured by peak blood flux (in mL/s) which develop at LV late diastole in sinus rhythm. VENC = velocity-encoded

Fig. 5. LV myocardial remodeling by CMR imaging in patient with AF.

Recent CMR technique provides assessment of myocardial ECV in LV wall derived from pre- and post-contrast T1 maps in patients with AF. In 40-year-old man with persistent AF, ECV map shows mean LV myocardial ECV of 31.69%. Usually, it has been widely accepted that mean LV myocardial ECV is less than 28% in healthy individuals without definite cardiomyopathy. ECV = extracellular volume fraction

Fig. 6. PV anatomy and LA by CCT images.

Isotropic voxel data from CCT scan can be reformatted into transverse (A) and coronal (B) multiplanar images. 3D volume rendering image (C) of CCT reveals stereoscopic view inside LA chamber and PV ostium. In 3D volume rendering images of PVs, typical anatomy comprises four PVs with separate ostia (D). Atypical PV anatomy mainly comprises common ostia for left PVs (arrow) (E) and additional right middle PV (arrow) (F). CCT = cardiac computed tomography

Fig. 7. Evaluation of PV by CMR imaging.

TR-MRA shows sequential contrast enhancement of large vessels from PA (A), through LA and aorta (B), to IVC (C). Multi-phase images by TR-MRA allows reconstruction of 3D models including CS, IVC, right atrium and LA. CS = coronary sinus, IVC = inferior vena cava, PA = pulmonary artery, TR-MRA = time-resolved magnetic resonance angiography

Fig. 8. Electroanatomic mapping.

Electroanatomic maps can help guide catheters (arrow) (A), reveal process of ablation lines (B), and fuse between LA model from cardiac image data and shell of electrophysiologic study (C) during catheter ablation of AF.

Fig. 9. Ablation-induced LA scar by 3D LGE-CMR imaging.

Post-procedural 3D LGE-CMR image shows thick LA wall areas of bright signal intensity (arrowheads) due to ablation-induced LA scar near RSPV. Post-procedural 3D LA model by LGE reveals ablation lines (arrowheads) surrounding LA antrum for electrical isolation of RSPV.

Fig. 10. Enlargement of LAA after catheter ablation of AF.

Post-procedural 3D LGE-CMR image shows thick LA wall areas of bright signal intensity (arrows) due to ablation-induced LA scar near ostium of LAA. Compared with pre-procedural CMR images, dimension of LAA ostium (red box) was decreased although chamber of LAA was enlarged. Volume of LAA increased from 49.6–61.7 mL after catheter ablation of AF.

Fig. 11. PV stenosis in 50-year-old male who underwent catheter ablation of AF.

Transverse chest CT image (A) shows interstitial edema and consolidation of left lung lower lobe. Chest CT image (B) with mediastinal window set shows interstitial edema and luminal narrowing of LIPV (arrow). Conventional angiography (C) also shows focal narrowing of LIPV as PV stenosis (arrow). Six-month follow-up cardiac CT image (D) shows in-stent restenosis (arrow) after stent insertion for PV stenosis.

Fig. 12. Atrioesophageal fistula in 43-year-old male who underwent catheter ablation of AF.

Electroanatomic map (A) shows multiple ablation points forming antrum ablation line (arrow) for electrical isolation of LSPV just anterior to Eso (arrowhead). Transverse chest CT image (B) shows small air-bubble (arrow) near LSPV. Sagittal reformatting image of chest CT (C) shows air-bubbles (arrow) between ESo (arrowhead) and LA. Fluid-attenuated inversion recovery magnetic resonance image of brain (D) reveals embolic stroke with multiple foci of bright signal intensity in bilateral cerebral hemispheres. Eso = esophagus