Epicardial electroanatomical mapping, radiofrequency ablation, and lesion imaging in the porcine left ventricle under real-time magnetic resonance imaging guidance-an in vivo feasibility study

Abstract

Aims: Magnetic resonance imaging (MRI) is the gold standard for defining myocardial substrate in 3D and can be used to guide ventricular tachycardia ablation. We describe the feasibility of using a prototype magnetic resonance-guided electrophysiology (MR-EP) system in a pre-clinical model to perform real-time MRI-guided epicardial mapping, ablation, and lesion imaging with active catheter tracking.

Methods and results: Experiments were performed in vivo in pigs (n = 6) using an MR-EP guidance system research prototype (Siemens Healthcare) with an irrigated ablation catheter (Vision-MR, Imricor) and a dedicated electrophysiology recording system (Advantage-MR, Imricor). Following epicardial access, local activation and voltage maps were acquired, and targeted radiofrequency (RF) ablation lesions were delivered. Ablation lesions were visualized in real time during RF delivery using MR-thermometry and dosimetry. Hyper-acute and acute assessment of ablation lesions was also performed using native T1 mapping and late-gadolinium enhancement (LGE), respectively. High-quality epicardial bipolar electrograms were recorded with a signal-to-noise ratio of greater than 10:1 for a signal of 1.5 mV. During epicardial ablation, localized temperature elevation could be visualized with a maximum temperature rise of 35 °C within 2 mm of the catheter tip relative to remote myocardium. Decreased native T1 times were observed (882 ± 107 ms) in the lesion core 3-5 min after lesion delivery and relative location of lesions matched well to LGE. There was a good correlation between ablation lesion site on the iCMR platform and autopsy.

Conclusion: The MR-EP system was able to successfully acquire epicardial voltage and activation maps in swine, deliver, and visualize ablation lesions, demonstrating feasibility for intraprocedural guidance and real-time assessment of ablation injury.

Figure 1

Intracardiac EGM signal quality, epicardial activation, and voltage maps. (A) Representative intracardiac EGM from the epicardium showing a peak amplitude of 14.56 mV (0.97 mV noise level)—sweep speed 100 mm/s. (B) For a low voltage 1.5 mV signal, a noise level of 0.136 mV is present giving a >10:1 signal-to-noise ratio. (C) Epicardial activation map in swine in sinus rhythm generated using active catheter tracking only in the MR environment. (D) Epicardial voltage map with threshold set between 0.5 mV and 1.5 mV. (E) Epicardial voltage map with a threshold set between 4.0 mV and 8.0 mV. 3D shells shown were created following segmentation of the whole heart sequence from MRI and imported into the iCMR application. Activation and voltage map data were superimposed onto the anatomical shells.

Figure 2

In vivo Δtemperature maps (A) shown at different time points relative to the start of the RF heating. Localized temperature elevation can be clearly visualized on the epicardial side of the left ventricle. Temporal profiles (B) obtained using CMR-thermometry during epicardial ablation in swine. A maximum temperature elevation of 35 °C was observed in a pixel within 2 mm of the catheter tip—Point 1 (relative to a more remote pixel in myocardium >8 mm away from the catheter tip—Point 3). No significant temperature elevation was observed in a pixel located in a remote area. 2D lesion dimensions measured using MR-dosimetry (C) correlate well with measurements on gross macroscopy with mild overestimation of lesion width.

Figure 3

Native T1 maps at six slices (apical to basal) 3–5 min following delivery of an ablation lesion (A) decreased T1 times were seen in the lesion core whilst elevated T1 times were seen in the surrounding tissue relative to non-ablated myocardium (ablation lesion core in white arrows). Mean native T1 time in the lesion core was 882 ms (±107 ms), in surrounding tissue was 1316 ms (±85 ms), and 1028 ms (±64 ms) in remote, non-ablated tissue (B); n = 10 lesions; *P < 0.05.