Nonfluoroscopic localization of an amagnetic stimulation catheter by multichannel magnetocardiography

This study was performed to: (1) evaluate the accuracy of noninvasive magne tocardiographic (MCG) localization of an amagnetic stimulation catheter; (2 ) validate the feasibility of this multipurpose catheter; and (3) study the characteristics of cardiac evoked fields. A stimulation catheter specially designed to produce no magnetic disturbances was inserted into the heart o f five patients after routine electrophysiological studies. The catheter po sition was documented on biplane cine x-ray images. MCG signals were then r ecorded in a magnetically shielded room during cardiac pacing, Noninvasive localization of the catheter's Sip and stimulated depolarization was comput ed from measured MCG data using a moving equivalent current-dipole source i n patient-specific boundary element torso models. In all five patients, the MCG localizations were anatomically in good agreement with the catheter po sitions defined from the x-ray images. The mean distance bet ween the posit ion of the tip of the catheter defined from x-ray fluoroscopy and the MCC l ocalization was 11 +/- 4 mm. The mean three-dimensional difference between the MCG localization at the peak stimulus and the MCG localization, during the ventricular evoked response about 3 ms later, was 4 +/- 1 mm calculated from signal-averaged data. The 95% confidence interval of beat-to-beat loc alization of the tip of the stimulation catheter from ten consecutive beats in the patients was 4 +/- 2 mm. The propagation velocity of the equivalent current dipole between 5 and 10 ms after the peak stimulus was 0.9 +/- 0.2 m/s. The results show that the use of the amagnetic catheter is technicall y feasible and reliable in clinical studies, The accurate three-dimensional localization of this multipurpose catheter by multichannel MCG suggests th at the method could be developed toward a useful clinical tool during elect rophysiological studies.