Terenz Escartin, MSc: No financial relationships to disclose
Christopher C. Cheung, MD MPH FRCPC: No financial relationships to disclose
Background: Catheter ablation is a well-established treatment option for ventricular tachycardia (VT) that has been shown to decrease mortality in patients with drug-refractory arrhythmias. However, there is a need for accurate ablation lesion imaging to better assess lesion formation and size. Native T1-weighted (NT1) MRI has demonstrated the potential to visualize ablation lesions in preclinical models without the need for contrast agents. NT1 exploits the intrinsic T1 contrast of methemoglobin present in thermally injured cardiomyocytes as a result of radiofrequency (RF) ablation. We sought to address the research gap in clinical translation and validation of NT1 MRI in patients undergoing catheter ablation.
METHODS AND RESULTS: For this study, we recruited five male patients (3 with implanted devices, 4 ischemic VT, 1 fascicular VT) undergoing catheter ablation. Electroanatomical maps and ablation tags were generated using a clinical electrophysiology software. All patients underwent cardiac magnetic resonance imaging (MRI) using a 1.5 Tesla scanner less than one week after the ablation procedure. Cine, NT1, and late gadolinium enhancement (LGE) MRI were performed in an approximately 1-hour scan (Fig. 1). NT1 and LGE utilized a custom 3D respiratory-gated LGE sequence at 2mm isotropic resolution with inversion times of (700, 220)ms, respectively. NT1 used 2RR cardiac gating, and LGE used 1RR cardiac gating. The MRI images were analyzed by one observer and segmented into 3D shells using a commercial software (Fig. 2).
NT1 MRI was feasible and safe early after the ablation procedure in patients with and without implanted devices, with no adverse effects. NT1 images demonstrated excellent visualization of the ablation lesions in territories that matched the LGE images and clinical ablation tags in 5/5 patients. Hyperintensities in NT1 images should arise from regions of ablated cardiomyocytes. As such, ablated regions of fibrosis will not appear bright in NT1. When compared to LGE imaging, NT1 is advantageous for ablation lesion characterization due to the endogenous tissue contrast and the selectivity of ablated tissue in the presence of edema. Image quality is currently limited by motion artifacts from the high-signal intensity fat of the chest wall and off-resonance artifacts from the implanted devices, when present.
Conclusion: This first in-human demonstration of NT1 MRI for post-ablation lesion visualization demonstrates clinical potential and translatability for this method. Further development is needed to include fat saturation to reduce artifacts, and additional clinical studies are needed to correlate post-ablation lesion visualization with subsequent tissue evolution.
