ABSTRACT
BACKGROUND: Extraction of the weak electrical activity of the "His Bundle" (HB) by noninvasive methods has not been very successful in the past. The study reassesses the use of signal averaged magnetocardiography (SAMCG), overcoming some of the limitations in earlier studies including in the signal averaging methodology. METHODS: SAMCG on healthy subjects (14 male and 1 female) were performed using R-peak as the fiducial point in all cases and also using QRS-onset as the fiducial point in select cases. RESULTS: A conspicuous feature (H) with a magnitude up to 200 femto Tesla (fT) attributed to the HB activity was observed in the PR segment at several spatial positions on the thorax, with onset at 35-50 ms before the QRS-onset (V) in 15 out of 18 trials constituting 83% of cases studied. The QRS-onset as the fiducial point resolved the feature better compared to the conventionally used R-peak, especially in trials exhibiting spread in heart rate (HR). This is attributed to the fluctuations in Q(on) RD (the time interval between QRS-onset and R-peak) compared to the temporal stability of the H-V duration. conclusions: SAMCG reveals a well-resolved H feature. The double hump morphology of the feature extended at least up to a frequency of 150 Hz. The importance of the choice of QRS-onset as the fiducial point is unequivocally demonstrated, illustrated by measurements on subjects exhibiting considerable heart rate variability. The latter has a general validity and should be applicable to SAECG as well.