Elsevier

Heart Rhythm

Volume 8, Issue 2, February 2011, Pages 295-303
Heart Rhythm

Experimental
Real-time magnetic resonance imaging–guided radiofrequency atrial ablation and visualization of lesion formation at 3 Tesla

https://doi.org/10.1016/j.hrthm.2010.10.032Get rights and content

Background

Magnetic resonance imaging (MRI) allows visualization of location and extent of radiofrequency (RF) ablation lesion, myocardial scar formation, and real-time (RT) assessment of lesion formation. In this study, we report a novel 3-Tesla RT -RI based porcine RF ablation model and visualization of lesion formation in the atrium during RF energy delivery.

Objective

The purpose of this study was to develop a 3-Tesla RT MRI-based catheter ablation and lesion visualization system.

Methods

RF energy was delivered to six pigs under RT MRI guidance. A novel MRI-compatible mapping and ablation catheter was used. Under RT MRI, this catheter was safely guided and positioned within either the left or right atrium. Unipolar and bipolar electrograms were recorded. The catheter tip–tissue interface was visualized with a T1-weighted gradient echo sequence. RF energy was then delivered in a power-controlled fashion. Myocardial changes and lesion formation were visualized with a T2-weighted (T2W) half Fourier acquisition with single-shot turbo spin echo (HASTE) sequence during ablation.

Results

RT visualization of lesion formation was achieved in 30% of the ablations performed. In the other cases, either the lesion was formed outside the imaged region (25%) or the lesion was not created (45%) presumably due to poor tissue–catheter tip contact. The presence of lesions was confirmed by late gadolinium enhancement MRI and macroscopic tissue examination.

Conclusion

MRI-compatible catheters can be navigated and RF energy safely delivered under 3-Tesla RT MRI guidance. Recording electrograms during RT imaging also is feasible. RT visualization of lesion as it forms during RF energy delivery is possible and was demonstrated using T2W HASTE imaging.

Introduction

Radiofrequency (RF) ablation1 has evolved from a primitive procedure to the mainstay of arrhythmia management it is today.2 As progress was made in the understanding of the mechanisms underlying arrhythmias, the limitations of fluoroscopy and conventional mapping techniques became apparent. Electroanatomic mapping allows for three-dimensional (3D) cardiac chamber reconstruction, spatial catheter localization, tissue characterization based on local electrograms (EGMs) and electrophysiologic tissue properties, and assessment of adequate RF energy delivery. Reduction in local tissue EGM voltage remains a widely used, albeit indirect, method for assessing adequate lesion formation. Electroanatomic mapping has become the cornerstone of modern, complex cardiac ablations.

A more effective endpoint for RF ablation would be direct, real-time (RT) visualization of myocardial destruction to assess lesion formation during ablation. Magnetic resonance imaging (MRI) allows for the assessment of location and extent of RF ablation lesion and of scar formation in the myocardium.3 However, assessment of lesion formation during RF energy delivery has remained elusive. Several groups have reported MRI tracking of catheters within the cardiac chambers with successful delivery of RF energy and postprocedure visualization of lesion formation in 1.5-Tesla scanners.4, 5, 6, 7 This is feasible using MRI; however, to the best of our knowledge, the ability to combine RT MRI tracking of electrophysiology (EP) catheters and recording of EGMs, with actual tissue and lesion formation visualization during RF ablation, has not been described yet. A system integrating these would prove valuable because it would allow visualization of a “hard” endpoint to ablation: direct, RT visualization of myocardial scar formation and its correlation with changes in tissue electrophysiologic properties.

In this study, we report a novel 3-Tesla RT MRI-guided catheter tracking system combined with a unique RT MRI sequence and a new T2-weighted (T2W) sequence, which have allowed us to successfully and safely position an EP catheter within the atria, record intracardiac EGMs, and ablate with simultaneously RT visualization of RF myocardial lesion as it is being formed.

Section snippets

Catheter description and energy delivery

A 110-cm 7F, 3-mm-tip, steerable, MRI-compatible ablation catheter (SurgiVision Inc., Irvine, CA, USA) was designed to deliver RF energy under 3-Tesla RT MRI. The catheter offered impedance monitoring and unipolar and bipolar EGM recording, and was able to deliver up to 40 W of energy in a power-controlled mode. It had four tracking microcoils. Figure 1A depicts a prototype EP-MRI catheter with a close-up view showing the catheter tip and the tracking coils in a deflected catheter.

Intracardiac

Catheter testing, navigation, and recording of intracardiac EGMs

The catheter underwent heat testing at 3 Tesla and found to be less than 2° above baseline during RT MRI. The tracking elements allowed for catheter visualization during navigation. Navigation was tried at different frame rates by different operators. It was found that 5.5 fps provided a reasonable balance between good visual resolution and imaging time for all operators. Hence, our RT MRI guidance was performed using an RT GRE pulse sequence at 5.5 fps.

Discussion

MRI-guided ablation within the atrium has recently been reported by other groups.6, 7 In one of these studies, MRI angiography of the atrium was acquired. The atrium surface was segmented, and RT catheter navigation was carried out using this 3D reconstruction. However, no images were acquired during ablation.6 Rather, immediately postablation, lesion formation was confirmed by LGE imaging. In the other study, the catheters were navigated using RT MRI sequences.7 However, there was no immediate

References (14)

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S. Vijayakumar, Dr. Kholmovski, G. Payne, and Dr. Marrouche are partially supported by grant from SurgiVision Inc. Dr. Vij and M. Guttman are employees of SurgiVision Inc.

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