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MRI-compatible voltage-based electroanatomic mapping system for 3T MR-guided cardiac electrophysiology: swine validations

Background

MRI provides luminal, edema, & scar images which assist in the Electrophysiological (EP) treatment of ventricular and atrial arrhythmias]. Until a complete set of MR-compatible EP-devices is available, patients must be repeatedly moved between the MRI, where imaging and mapping occur, to the conventional EP suite, where puncture, navigation and Radio-Frequency Ablation occur. MRI-conditional voltage-based electroanatomic mapping (EAM) would permit efficient MRI-guided EP, with registration-free continuation outside MRI, utilizing X-ray, Intra-Cardiac-Echo (ICE) and EAM guidance. A 1.5T EnSite™ Velocity™ cardiac mapping system, a voltage-based EAM available from St. Jude Medical was previously validated [1, 2]. Multiple-catheter EAM (localization and intra-cardiac electrocardiogram (EGM) measurement) inside a 3T MRI requires modifications.

Methods

An EnSite™ Velocity™ system was connected to an electronic switching circuit that prevents induced MRI gradient-ramp noise from corrupting ECG fidelity. Electrode tracking is preserved with software blanking. The system also included RF-filtered electrical lines, modified EnSite™ NavX™surface electrodes, and gold electrode EP catheters [2]. Trans-septal punctures were made in 2 intubated swine under X-ray & ICE guidance. Millar catheters were placed in the aorta to monitor Invasive Blood Pressure (IBP). The swine were moved to a Siemens 3.0T MRI suite equipped with an EnSite™ Velocity™ system. A 12-lead MRI-compatible ECG [3] was also used. Three EP catheters, with 4 voltage-tracked electrodes each, were navigated simultaneously inside the MRI to acquire EAM of the heart's left & right sides, with a coronary sinus catheter for physiological reference. Imaging & EAM were performed simultaneously (Figure 1). To measure the EnSite™ Velocity™ system's catheter tracking accuracy during MR imaging, catheters were navigated to specific anatomic regions, and the change in location was observed during imaging over 10 sec increments.

Figure 1
figure1

EAM maps acquired (A) outside MRI versus (B) inside the 3T MRI. Three simultaneously navigated catheters (LA, RA#1 and RA#2) are shown. Upper images show EAM maps. Lower images show surface ECG, intra-cardiac EGM (RA#1, RA#2 and LA catheter tip electrodes), as well as intra-aortic IBP traces. QRS denotes start of ECG cycle. V and A denote Ventricular and Arterial signals, respectively. A strong superimposed ventricular signal was observed on all atrial intra-cardiac ECG traces (extreme-right red vertical line in (B)) acquired inside the MRI, a result of the strong 3T Magnetohydrodynamic voltage.

Results

EAM & catheter navigation in swine were performed both inside & outside the MRI at >20 frames-per-second without re-registration (Figure 1). Imaging was conducted simultaneously with tracking, with catheter position stable (+1 mm) during imaging in TR>32 ms sequences. Median catheter electrode locations changed by < 0.5 mm between inside and outside MRI. An added ventricular signal was observed on intra-MRI atrial EGMs (Figure 1B), due to Magnetohydrodynamics. IBP detected a cardiac event (Figure 2), followed by successful CPR & defibrillation in the MRI suite. MRI Image quality reduction was < 5%, although catheter artifacts during SSFP were excessive (Figure 3), requiring catheter redesign.

Figure 2
figure2

Surface ECGs, EGMs (Intra-cardiac ECGs) and IBP traces taken before, during, and after successful resuscitation (compression and defibrillation) of a cardiac event which occurred inside the MRI. The cardiac event was recorded during mapping of the base of the swine's Left Atrium.

Figure 3
figure3

The three EP catheters (LA, RA#1 and RA#2) were passively detected in multi-slice SSFP cine images as a result of over-tipping (red and yellow arrows) on the catheter shaft as well as susceptibility artifacts (blue arrows) at the tip.

Conclusions

3T MRI-conditional voltage tracking allows simultaneous catheter tracking & MR imaging, permitting registration-free EAM inside & outside MRI during EP procedures.

Funding

NIH U41-RR019703 & R03-EB013873-01A1, AHA 10SDG261039.

References

  1. 1.

    ZTH Tse SCMR. 12-13.

  2. 2.

    EJ Schmidt MRM. 13-

  3. 3.

    ZTH TSE MRM. 13-

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Correspondence to Ehud J Schmidt.

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Zhang, S.H., Tse, Z.T., Dumoulin, C.L. et al. MRI-compatible voltage-based electroanatomic mapping system for 3T MR-guided cardiac electrophysiology: swine validations. J Cardiovasc Magn Reson 16, P140 (2014). https://doi.org/10.1186/1532-429X-16-S1-P140

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Keywords

  • Invasive Blood Pressure
  • Image Quality Reduction
  • Catheter Tracking
  • Electroanatomic Mapping System
  • Coronary Sinus Catheter