Markku Mäkijärvi

Detection of Exercise‐Induced Myocardial Ischemia by Multichannel Magnetocardiography in Single Vessel Coronary Artery Disease

Background: Detection of myocardial ischemia was studied with multichannel exercise magneto‐cardiography (MCG). A surface gradient method was applied to analyze cardiac magnetic fields.

On the accuracy of source localisation in cardiac measurements (magnetocardiography)

This paper describes a localisation study of the sources of bioelectrical activity in the human heart. In particular, the atrial activation (P wave) and the activation of an extra pre-excitation area in the WPW syndrome are investigated. Different models based on the current multipole expansion are used to calculate the inverse solution. A comparison between calculated results, invasive electrophysiological studies and known physiological data is performed. The best results were obtained by the current multipole model with dipole and quadrupole terms. Non-invasive localisation of cardiac electric sources can be useful in studies of arrhythmia patients in the future.

Nonfluoroscopic Localization of an Amagnetic Catheter in a Realistic Torso Phantom by Magnetocardiographic and Body Surface Potential Mapping

This study was performed to evaluate the accuracy of multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) in localizing three‐dimensionally the tip of an amagnetic catheter for electrophysiology without fluoroscopy. An amagnetic catheter (AC), specially designed to produce dipolar sources of different geometry without magnetic disturbances, was placed inside a physical thorax phantom at two different depths, 38 mm and 88 mm below the frontal surface of the phantom. Sixty‐seven MCG and 123 BSPM signals generated by the 10 mA current stimuli fed into the catheter were then recorded in a magnetically shielded room. Non‐invasive localization of the tip of the catheter was computed from measured MCG and BSPM data using an equivalent current dipole source in a phantom‐specific boundary element torso model. The mean 3‐dimensional error of the MCG localization at the closer level was 2 ± 1 mm. The corresponding error calculated from the BSPM measurements was 4 ± 1 mm. At the deeper level, the mean localization errors of MCG and BSPM were 7 ± 4 mm and 10 ± 2 mm, respectively. The results showed that MCG and BSPM localization of the tip of the AC is accurate and reproducible provided that the signal‐to‐noise ratio is sufficiently high. In our study, the MCG method was found to be more accurate than BSPM. This suggests that both methods could be developed towards a useful clinical tool for nonfluoroscopic 3‐dimensional electroanatomical imaging during electrophysiological studies, thus minimizing radiation exposure to patients and operators.

Magnetocardiographic Pacemapping for Nonfluoroscopic Localization of Intracardiac Electrophysiology Catheters

The purpose of the study was to validate, in patients, the accuracy of magnetocardiography (MCG) for three‐dimensional localization of an amagnetic catheter (AC) for multiple monophasic action potential (MAP) with a spatial resolution of 4 mm2. The AC was inserted in five patients after routine electrophysiological study. Four MAPs were simultaneously recorded to monitor the stability of endocardial contact of the AC during the MCG localization. MAP signals were band‐pass filtered DC‐500 Hz and digitized at 2 KHz. The position of the AC was also imaged by biplane fluoroscopy (XR), along with lead markers. MCG studies were performed with a multichannel SQUID system in the Helsinki BioMag shielded room. Current dipoles (5mm; 10mA), activated at the tip of the AC, were localized using the equivalent current dipole (ECD) model in patient‐specific boundary element torso. The accuracy of the MCG localizations was evaluated by: (1) anatomic location of ECD in the MRI, (2) mismatch with XR. The AC was correctly localized in the right ventricle of all patients using MRI. The mean three‐dimensional mismatch between XR and MCG localizations was 6 ± 2 mm (beat‐to‐beat analysis). The coefficient of variation of three‐dimensional localization of the AC was 1.37% and the coefficient of reproducibility was 2.6 mm. In patients, in the absence of arrhythmias, average local variation coefficients of right ventricular MAP duration at 50% and 90% ofrepolarization, were 7.4% and 3.1%, respectively. This study demonstrates that with adequate signal‐to‐noise ratio, MCG three‐dimensional localizations are accurate and reproducible enough to provide nonfluoroscopy dependant multimodal imaging for high resolution endocardial mapping of monophasic action potentials.

Magnetocardiographic localization of a non-magnetic pacing catheter

The position of a non-magnetic pacing catheter was localized non-invasively from multichannel magnetocardiographic (MCG) measurements in 5 patients. A catheter specially designed to produce no magnetic disturbances was inserted in the heart after standard electrophysiological studies. Its position was recorded on cine X-ray images; thus the catheter was serving as an exactly defined current-dipole source. Magnetocardiograms were then recorded in a magnetically shielded room during cardiac pacing, and the MCG localization was performed using boundary element torso models. The MCG localizations were in good agreement with the catheter positions defined from the X-ray images; the average difference between these locations was 22/spl plusmn/6 mm.

Exercise magnetocardiography in healthy subjects and single vessel coronary artery disease patients

Exercise induced ischemia was detected using a novel method for calculating the orientation of magnetic field at ST-segment and T-wave. Magnetocardiographic mapping was performed during supine physical exercise testing in 35 subjects including 23 patients with single vessel coronary artery disease. In 12 healthy controls exercise was found to induce a negative change in magnetic field at the ST-segment and T-wave. This prevented the use of similar amplitude parameters as in electrocardiography for the separation of patients and controls.