Magnetocardiographic and Electrocardiographic Mapping Studies

Abstract

The electrical activity of the heart can be monitored electrically with electrodes or magnetically using SQUIDS. With multiple measuring sites, covering a significant portion of the upper torso, Body Surface Potential Maps (BSPMs) or Magnetic Field Maps (MFMs) can be constructed every 1 or 2 ms, providing detailed temporal and spatial information about cardiac electrical activity. Several methods are available to extract clinically useful parameters from this wealth of information. Using inverse solutions, cardiac function can be assessed, and cardiac events located. When such an event is implicated in arrhythmia, knowledge of the location of this site can be used to guide the catheter toward it for possible ablation. Lately, the BSPM technique has been used to record maps that result from endocardial catheter pacing. The resulting BSPM is characteristic for the pacing site, and when similar to the surface maps obtained during spontaneous arrhythmogenic events, the pacing catheter is assumed to be close to the cardiac tissue initiating the arrhythmia. This method of localization provides an alternative to the traditional inverse solutions based on numerical methods. A similar technique of matching patterns also can be used with MFMs. We review the different localization techniques that use MFMs and/or BSPMs. Such techniques, together with MRI, are now under development to provide the clinician with electrical images of the heart surface for the assessment of cardiac function. We also summarize results of the analysis of MFMs and BSPMs of the same patient or patient group with an emphasis on finding landmarks in such maps that are predictors of clinical cardiac events. The results obtained so far are encouraging for both BSPM and MFM. Systematic multichannel MFM studies with substantial patient populations are needed to demonstrate the clinical importance of cardiac magnetic field mapping. This new mapping method, made possible by recent developments in SQUID technology, could provide, by itself, or together with BSPM, a powerful, quick, non-invasive method to image electrical activity of the heart to assist in clinical diagnosis.