The Influence of biomagnetometer area-of-coverage in the determination of fetal cardiac time intervals

摘要

Aim of this work was to examine the effect of the acquisition system on the durations of fetal cardiac time intervals (CTI). Over 200 FMCGs of healthy fetuses, recorded between the 16th and 42nd week of gestation with either a 37 or a 61 channel biomagnetometer, were available for analysis. Two approaches were used to examine the averaged PQRST signals. First, using 21 FMCGs (7 around the 20th, 30th and 40th week) recorded with the 61 channel system, CTI (P wave, PQ interval, QRS complex) were determined on the basis of the timing of onset and end of the P wave and QRS complex using sets of 1, 7 and 61 channels and were compared. Second, the CTI durations as determined on the basis of the 61 channel system (n=121) and the 37 channel system (n=90) were compared. In the determination of the CTI, using more of the 61 available channels led to significantly longer P wave and QRS complex durations. This was particularly so for the P wave, on average 6 ms (>10%), and in earlier pregnancy. Comparing the CTI based on 37 and 61 channels showed minimal underestimation of the 37 channel data. The results showed that the duration of fetal CTI as determined on the basis of magnetocardiography were dependent on the number of channels available for analysis of the timing of P and QRS onset and offset. This dependency was stronger earlier in pregnancy and suggests that at least well-placed 7 channels should be available for the reliable determination of fetal CTI.