Image Integration Guided Catheter Ablation of Arrhythmias

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Transvenous catheter ablation has become a curative treatment for many arrhythmias. Knowing the precise catheter location in relation to true cardiac anatomy will benefit catheter ablation procedures. A novel electroanatomic mapping system (CartoMerge™, Biosense Webster) with the capability of integrating pre-procedural computed tomography (CT) or magnetic resonance (MR) images with electroanatomic maps has been recently approved for patient care. The employment of this system will improve catheter navigation and therefore may facilitate many catheter ablation procedures.


Clinical Need for Imaging-guided Intervention
Catheter navigation is traditionally guided by fluoroscopy, which provides only limited information about catheter location in relation to cardiac anatomy. Over the past decade, novel ablation strategies mostly based on anatomic considerations have been developed for the treatment of complex arrhythmias, such as atrial fibrillation and non-idiopathic ventricular tachycardia. In order to facilitate these procedures, various threedimensional (3-D) mapping systems have been developed that enable the realtime display of the ablation catheter in relation to the 3-D maps reconstructed from multiple endocardial locations. However, these mathematically reconstructed 3-D maps cannot replicate the true cardiac anatomy as displayed with CT or MR imaging. Therefore, a clinical need exists for a mapping system that is capable of realtime visualization of ablation catheter location in relation to the true cardiac anatomy provided by CT or MR imaging.

Rationale of Image Integration
Image integration refers to the process of aligning the pre-procedural cardiac CT/MR images with the realtime 3-D maps reconstructed from multiple endocardial locations. The new system is able to track and display the realtime catheter tip location and orientation relative to a reference catheter at a given time-point in the cardiac cycle. Thus, the 3-D electroanatomic maps reconstructed from multiple endocardial locations sampled by catheter navigation represent a snapshot of the mapped cardiac chambers at that time.The impact of respiratory motion or patient movement on the catheter tip location in relation to the 3-D electroanatomic maps is minimized by the reference catheter, which is placed on the patient’s back.This results in realtime display of the catheter tip in relation to the static 3-D electroanatomic maps.The system uses computerized algorithms to superimpose the pre-procedural cardiac CT/MR images onto the electroanatomic maps at the same point in the cardiac cycle and, therefore, enables the dynamic display of the catheter tip location on the true cardiac anatomy.

Steps of the Image Integration Process
The process of image integration consists of three steps: pre-procedural CT/MR imaging, image segmentation and extraction, and image registration.

CT/MR Imaging
To control the interval change, we recommend that patients undergo CT/MR imaging within 24 hours before the ablation procedure. In order to obtain high resolution images (0.5–1mm slice thickness), contrastenhanced CT scanning is performed during a single breath hold with the use of a 32-or 64-slice CT scanner. A simultaneous electrocardiogram (ECG) is recorded to retrospectively assign the source images to the respective phases of cardiac cycle. Axial images at the end diastole are reconstructed at 0.5–1mm interval and transferred to the system for image registration.

MR imaging (MRI) is an alternative image modality for the purpose of image integration. MR angiograms are obtained with a 1.5-T MRI system after intravenous gadolinium injection.With currently available MR scanners, non-ECG gated MR images with about 1–2mm spatial resolution can be obtained during a single breath hold. MRI is good for patients with renal dysfunction, which is a contraindication to contrastenhanced CT imaging./>/>/>/>/>/>/>/>/>/>/>/>



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