Acquisition and Analysis of fetal ECG

Task #1: Record and analyze fetal ECG

Record 8 channels of ECG data from the mother in order to find the fetal ECG. Independent Component Analysis (ICA) should be used to find the sources of the fetal signal.

Perform the following steps:

1. Place 8 ECG disposable electrodes onto the abdomen of the mother where you expect the heart of the baby. Arrange the 8 electrodes like shown in the MontageCreator below:


 

The electrode distance should be about 4-5 cm.
2. Connect g.USBamp to the notebook and start g.Recorder for the data acquisition. Connect the 8 electrodes shown in the MontageCreator to inputs 1-8 of the amplifier.



3. Place the ground electrode onto the foot of the mother and connect the cable to the G-Ground electrode socket of the amplifier
4. Place the reference electrode into the right lower corner of the 3 x 3 grid shown on the MontageCreator and connect it to the R-Reference input of the amplifier
5. Start g.Recorder and select 256 Hz. Check the data quality of the ECG channels and Record about 90 seconds of data. Use the filename FetalECG.hdf5
6. Load the data-set into g.BSanalyze to investigate the 8 channels:

 

  In the raw data the mothers ECG and the babies ECG is not visible without signal processing techniques because noise overlays the very small signals.
7. Open the Geometry window from the Header menu and Browse for the 8chmontage.mat file

 

 

  This loads the electrodes x- and y- coordinates into g.BSanalyze. This information is important for the ICA calculation in the next step.
8. Open the Independent Component Analysis (ICA) window form the Analyze menu and select higher order statistics (HOS) under ICA algorithm.

 

 

9. Check Save results and select the filename icafilter.mat to store the result of the analysis
10. Open the Spatial Filter window from the Pre-Processing menu and load the icafilter.mat file that was calculated in the previous step. The filter has a size of 8 x 8 because it was calculated of 8 ECG channels.

11.

 Select the Create temporal pattern function and enter under use filter(s) with number(s) [1:8] to use all 8 ICA filters
12. Select Replace all channels to remove the raw ECG data
13. Press Start to perform the Spatial Filtering. Finally the DataEditor show the ICA components of the 8 ECG channels and contains the ECG of the mother in channel 7 and the ECG of the baby in Channel 3. The other channels contain mainly noise (especially channel 4 contains the power line interference noise). Note the small amplitudes in the µV ranges of the data.

 

 

Task #2: Find QRS complexes and calculate HRV

Assign QRS markers to the ECGs of the mother and of the baby. Calculate and compare the heart-rate variability parameters in time domain.

 

1. Click on the Select button in the Data Editor to define new markers

 

 

2. Create a marker with the name FETALQRS and another marker with the name QRSmother. Close the window with OK

 


 

3. Now search for the QRS peaks of the mother and assign the QRSmother marker to each peak. The markers are indicated in blue color in the figure below:

4. Similarly assign the FETALQRS markers to the ECG channel 3. The markers are indicated in red color.

NOTE: You can also load the file ECGwithMarker.mat to avoid the manual editing

5. To calculate the heart-rate and heart-rate variability parameters in time domain open the HRV Time Domain function from the ECG menu

 

6. Select the QRSmother marker and set the Start interval to 5000 ms and End at to 60000 ms and set the Tachogram unit and Histogram unit to bpm
7. Check the Resample tachogram box then press Start
8. This calculates the Tachogram, the Histogram and the most important HRV parameters in the time domain of the mother. This calculates the Tachogram, the Histogram and the most important HRV parameters in the time domain of the mother. g.Result2d opens with the results:

 

 

 

  The heart-rate varies between 77 and 99 bpm. The histogram is quite narrow and the highest peak is 12. This means that 12 beats of the data segment had the same heart-rate.
9. Then perform the steps with the FETALQRS marker to obtain the following results:

 

 

The heart-rate varies now between 120 and 174 bpm. The histogram is much broader and only 10 beats had the same heart-rate.

The table below show the most important parameters for the mother. The MeanHR is 90.01 bpm, the RMSSD is 23.94 ms and the pNN50 is 3.7 %

For the baby the MeanHR is 150.48, the RMSSD is 17.38 and the pNN50 is 0.75 %. This means that the baby has a higher heart-rate and a lower heart-rate variability as the mother which is a quite common situation.
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