Abstract
PurposeLow-field (0.55 T) high-performance cardiovascular magnetic resonance (CMR) is an attractive platform for CMR-guided intervention as device heating is reduced around 7.5-fold compared to 1.5 T. This work determines the feasibility of visualizing cardiac radiofrequency (RF) ablation lesions at low field CMR and explores a novel alternative method for targeted tissue destruction: acetic acid chemoablation.MethodsN = 10 swine underwent X-ray fluoroscopy-guided RF ablation (6–7 lesions) and acetic acid chemoablation (2–3 lesions) of the left ventricle. Animals were imaged at 0.55 T with native contrast 3D-navigator gated T1-weighted T1w) CMR for lesion visualization, gated single-shot imaging to determine potential for real-time visualization of lesion formation, and T1 mapping to measure change in T1 in response to ablation. Seven animals were euthanized on ablation day and hearts imaged ex vivo. The remaining animals were imaged again in vivo at 21 days post ablation to observe lesion evolution.ResultsChemoablation lesions could be visualized and displayed much higher contrast than necrotic RF ablation lesions with T1w imaging. On the day of ablation, in vivo myocardial T1 dropped by 19 ± 7% in RF ablation lesion cores, and by 40 ± 7% in chemoablation lesion cores (p < 4e−5). In high resolution ex vivo imaging, with reduced partial volume effects, lesion core T1 dropped by 18 ± 3% and 42 ± 6% for RF and chemoablation, respectively. Mean, median, and peak lesion signal-to-noise ratio (SNR) were all at least 75% higher with chemoablation. Lesion core to myocardium contrast-to-noise (CNR) was 3.8 × higher for chemoablation. Correlation between in vivo and ex vivo CMR and histology indicated that the periphery of RF ablation lesions do not exhibit changes in T1 while the entire extent of chemoablation exhibits T1 changes. Correlation of T1w enhancing lesion volumes indicated in vivo estimates of lesion volume are accurate for chemoablation but underestimate extent of necrosis for RF ablation.ConclusionThe visualization of coagulation necrosis from cardiac ablation is feasible using low-field high-performance CMR. Chemoablation produced a more pronounced change in lesion T1 than RF ablation, increasing SNR and CNR and thereby making it easier to visualize in both 3D navigator-gated and real-time CMR and more suitable for low-field imaging.
Highlights
Catheter ablation is increasingly used to treat ventricular tachycardia (VT) in structural heart disease, but arrhythmia commonly recurs after ablation [1,2,3]
Though Two dimensional (2D) imaging sacrifices resolution, when imaging at low field, this study found that both RF and chemoablation lesions could be detected by 2D native contrast single-shot T1w Cardiovascular magnetic resonance (CMR) imaging with two heartbeat triggering
Accurate identification of tissue necrosis is the goal of ablation lesion characterization in CMR
Summary
Catheter ablation is increasingly used to treat ventricular tachycardia (VT) in structural heart disease, but arrhythmia commonly recurs after ablation [1,2,3]. Procedure failure is likely due to incomplete ablation of arrhythmogenic tissue. Performing cardiac ablation procedures under CMR guidance has been limited by the ability to distinguish permanent from transient tissue injury acutely after ablation [11], and the concern for CMR scanning induced heating of catheters and guidewires [12,13,14,15,16]. Accurate determination of radiofrequency (RF) ablation induced tissue necrosis is key for intra- or post-procedural lesion assessment. Gadolinium-based contrast agents have been applied but are not preferred as lesion hyperenhancement overestimates the extent of necrosis until days or weeks after ablation when transient tissue injury and edema have resolved [11, 17,18,19]. As we demonstrate in this work, assessment of lesion necrosis resulting from RF ablation using native T1 contrast is feasible at low field
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