Noninvasive fetal ECG mode fetal heart rate monitoring by adaptive digital filtering.

Beat-to-beat variability (BTBV) of the fetal heart rate (FHR) is considered an indication of the neural integrity and is an important prognostic indicator of fetal well-being. We report the initial evaluation of a recently developed abdominal fetal ECG (AFECG) mode of FHR monitoring using Adaptive Digital Filtering (ADF) to accurately obtain BTBV noninvasively. Five women in labor at term were monitored with the direct fetal scalp electrode (FSE) and simultaneously with the AFECG using ADF. A computer analysis of 3298 seconds (55 minutes) of data provided a one-to-one comparison of the R-R intervals. One analysis of the direct FSE data with a second simultaneous analysis from the same electrode, to serve as control, was compared with the noninvasive AFECG data. The study group has a standard deviation of only 1.50 bpm compared to 0.79 bpm for the control group. The AFECG method agrees with the direct FSE method within 1 bpm for 92.6% of the reported R-R intervals and within 2 bpm for 98.9% of the reported intervals. This new noninvasive AFECG technique with ADF provides a continuous record of instantaneous FHR and BTBV that may be relied upon to provide an accurate continuous clinical record. The reliability of the technique has yet to be determined over a wide range of subjects.

Adaptive filtering in ECG monitoring of the fetal heart rate.

There has long been an interest in noninvasively monitoring the fetal electrocardiogram (ECG). In the past twenty years a clinical need has developed to monitor the instantaneous fetal heart rate (FHR) and changes in the heart rate from one beat to the next, i.e., beat-to-beat FHR variability as well as an interest in understanding the development of cardiac arrhythmias. The purpose of this paper is to present initial results obtained from an Electrocardiographic Adaptive Processor (EAP) to noninvasively monitor in real-time continuous tracings of the fetal ECG, FHR, and FHR variability. Twenty-five sets of noninvasive fetal ECG data were collected from pregnant subjects during the third trimester of pregnancy using maternal abdominal paste-on electrodes. The fetal QRS amplitude and shape varied from 5 to 30 microvolts with fetal position, gestational age, and relative electrode configuration. Results have been obtained in three specific areas: 1) The development and initial testing of a microprocessor based Electrocardiographic Adaptive Processor (EAP) implemented as an FHR monitor has been completed. The EAP has been implemented to adaptively cancel, in real-time, the maternal ECG component from maternal abdominal ECG leads to provide a continuous tracing of the fetal ECG complex, or FHR and FHR variability. 2) Maternal and thoracic ECG data stored on computer disk were used to test the adaptive techniques to cancel the strong interfering maternal ECG. Studies continue to effectively reduce background electromyographic (EMG) noise. 3) Tracings of the fetal QRS complex, instantaneous FHR, and short term FHR variability have been obtained in real-time.(ABSTRACT TRUNCATED AT 250 WORDS)