The normal human magnetocardiogram. II. A multipole analysis.

This paper presents a multipole analysis of the QRS complex of the normal magnetocardiogram (MCG) of six normal subjects. The multipole strengths up to the octupole term were determined from the measured distribution of the z-component of the cardiac magnetic field (the component perpendicular to the frontal plane). This equivalent magnetic multipole generator was found to represent the cardiac magnetic field with a minimum error of less than 10%. The dipolar term of the expansion was found to represent the field distribution with reasonable accuracy early during ventricular activation, whereas late during activation, the higher multipole terms were clearly more significant.

The normal magnetocardiogram: I Morphology.

This paper presents a morphological study of the real-time magnetocardiogram (MCG) of normal subjects. The MCGs were obtained using a gradiometric measurement technique, and the magnetic field component perpendicular to the frontal plane (z-compenent) was studied. Forty-one healthy men and women were mapped from 51 positions on the chest, and the statistics of the waveforms of the MCG were computed. In 21 of the subjects both the MCG and the ECG were analyzed. The general behaviour of the MCGs is discussed and proposals for the standardization of the measurements are made.

Instantaneous fetal heart rate monitoring by electromagnetic methods.

Fetal magnetocardiography (FMCG) is a new complementary external method for accurate antepartal FHR recording. Because of the low magnetic noise level required it is not yet suitable for routine hospital use. Fifty-six simultaneous FMCG and external FECG measurements were made in order to compare these methods for instantaneous FHR recording. The error of the FHR value obtained with the instrumentation described is less than 1 per cent. Our results show that FMCG can be used for FHR processing from week 30 of gestation until term. Thirty-five of the measurements were done during this period. From these, a readable FHR curve was obtained in 21 cases with FMCG and in 12 cases with external FECG. The maternal complexes were always present in the FECG, but in only 15 of the recorded FMCG's.

Detection of fetal QRS-complexes by external methods.

A new method is presented for detection of the QRS complexes and the fetal heart rate from the fetal magnetocardiogram and from the fetal electrocardiogram. In the method, the amplitude, the polarity and the shape of the QRS complex are tested. By using the described equipment it is possible to detect all consecutive heart beat intervals from a fetal electrocardiogram with less than 1% error in timing. When an external fetal electrocardiogram was used for testing, generally slightly over 10% of the QRS complexes were lost since they were simultaneous with the maternal complexes. In addition, complexes were also lost due to noise.