Feasibility of real-time magnetic resonance imaging for catheter guidance in electrophysiology studies

Abstract

Background: Compared with fluoroscopy, the current imaging standard of care for guidance of electrophysiology procedures, magnetic resonance imaging (MRI) provides improved soft-tissue resolution and eliminates radiation exposure. However, because of inherent magnetic forces and electromagnetic interference, the MRI environment poses challenges for electrophysiology procedures. In this study, we sought to test the feasibility of performing electrophysiology studies with real-time MRI guidance.

Methods and results: An MRI-compatible electrophysiology system was developed. Catheters were targeted to the right atrium, His bundle, and right ventricle of 10 mongrel dogs (23 to 32 kg) via a 1.5-T MRI system using rapidly acquired fast gradient-echo images (approximately 5 frames per second). Catheters were successfully positioned at the right atrial, His bundle, and right ventricular target sites of all animals. Comprehensive electrophysiology studies with recording of intracardiac electrograms and atrial and ventricular pacing were performed. Postprocedural pathological evaluation revealed no evidence of thermal injury to the myocardium. After proof of safety in animal studies, limited real-time MRI-guided catheter mapping studies were performed in 2 patients. Adequate target catheter localization was confirmed via recording of intracardiac electrograms in both patients.

Conclusions: To the best of our knowledge, this is the first study to report the feasibility of real-time MRI-guided electrophysiology procedures. This technique may eliminate patient and staff radiation exposure and improve real-time soft tissue resolution for procedural guidance.

Figures

Figure 1

Schematic of the MRI-compatible pacing and electrogram acquisition system. The system consists of a nonmagnetic filter box that rejects the 64-MHz imaging frequency from the MRI scanner. The preamplifier is a Sensorium EPA-6 16 channel amplifier module with clinical-grade isolation. An AD Instruments PowerLab converter digitizes the output from the EPA-6. Digital data are sent to the data acquisition computer through the fiberoptic link, which forms an additional isolation barrier. The EPI-3 stimulation unit provides pacing output and is a clinical-grade unit. Electrograms are displayed in real time for the electrophysiologist via the slave monitor in the procedure suit. Additional isolation is provided by the clinical-grade isolation transformer and the fiberoptic link from the electronics inside and outside the MRI scanner suite. SCSI indicates Small Computer System Interface.

Figure 2

Mean temperature at the tip and ring electrodes of the passive tracking catheter in 5-second increments for 27 different phantom test permutations in catheter shape, catheter position, and MRI sequences with worst-case-scenario SAR up to 4 W/kg. Error bars reflect the SEM.

Figure 3

Real-time guidance of a passive catheter to the His bundle position in the canine model. A, Catheter bipolar electrodes (Bi) are shown in the inferior vena cava. B, The catheter is advanced, with tip (arrow) entering hepatic vein. C, Catheter buckling as a result of advancement into a hepatic vein. D, The catheter tip is withdrawn into the inferior vena cava. E, The catheter tip is advanced beyond the hepatic vein branch in the inferior vena cava. F, The catheter tip is advanced to the tricuspid annulus. SVC indicates superior vena cava; L, liver; RV, right ventricle; and RA, right atrium.

Figure 4

Difference in visibility of active (capable of receiving MRI signal) and passive catheters on MRI images of the canine model. A, The active catheter is shown advancing through the inferior vena cava to the right ventricle. The active (bright) signal created by the catheter helps to identify its position within the image. B, The passive catheter is shown advancing through the inferior vena cava to the right ventricle. Passive visualization uses the signal void created by the catheter body or local susceptibility artifact of the platinum electrode to identify the catheter position within the image.

Figure 5

Unfiltered and filtered intracardiac electrograms obtained via the canine model inside the MRI scanner during GRE imaging. The tracings in each column are simultaneous. The electrogram gain across each row is constant. RA indicates right atrium catheter electrogram; His, His catheter electrogram; RV, right ventricular catheter electrogram; A, atrial signal; H, His signal; and V, ventricular signal.

Figure 6

Pace stimulation in the canine model from the right atrium (A) and right ventricle (B) in the MRI scanner. In each case, myocardial capture is confirmed via multiple intracardiac electrograms and the surface ECG lead II.

Figure 7

Gradient signal–induced noise during MRI guidance of an electrophysiology catheter in a patient. The SNR is much improved in the filtered electrogram.