Reproducibility of HTS-SQUID magnetocardiography in an unshielded clinicalenvironment

A new technology has been developed which measures the magnetic field of th e human heart {magnetocardiogram, MCG) by using high temperature supercondu cting (HTS) sensors. These sensors can be operated at the temperature of li quid nitrogen without electromagnetic shielding. We tested the reproducibil ity of HTS-MCG measurements in healthy volunteers. Unshielded HTS-MCG measu rements were performed in 18 healthy volunteers in left precordial position in two separate sessions in a clinical environment. The heart cycles of 10 min were averaged, smoothed, the baselines were adjusted, and the data wer e standardized to the respective areas under the curves (AUC) of the absolu te values of the QRST amplitudes. The QRS complexes and the ST-T intervals were used to assess the reproducibility of the two measurements. Ratios (R- QRS, R-STT) were calculated by dividing the AUC of the first measurement by the ones of the second measurement. The linear correlation coefficients (C ORRQRS, CORRSTT) of the time intervals of the two measurements were calcula ted, too. The HTS-MCG signal was completely concealed by the high noise lev el in the raw data. The averaging and smoothing algorithms unmasked the QRS complex and the ST segment. A high reproducibility was found for the QRS c omplex (R-QRS=1.2 +/-0.3, CORRQRS=0.96 +/-0.06). Similarly to the shape of the ECG it was characterized by three bends, the Q, R, and S waves. In the ST-T interval, the reproducibility was considerably lower (R-STT=0.9 +/-0.2 , CORRSTT=0.66 +/-0.28). In contrast to the shape of the ECG, a baseline de flection after the T wave which may belong to U wave activity was found in a number of volunteers. HTS-MCG devices can be operated in a clinical envir onment without shielding. Whereas the reproducibility was found to be high for the depolarization interval, it was considerably lower for the ST segme nt and for the T wave. Therefore, before clinically applying HTS-MCG system s to the detection of repolarization abnormalities in acute coronary syndro mes, further technical development of the systems is necessary to improve t he signal-to-noise ratio. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.