The ECG Analysis Module is unable to detect the end of the T wave if there is too much low-frequency noise in the signal. Adding a High-Pass Filter at 2Hz* will remove the low-frequency artifact caused by the breathing of the animal.
*Please note the cutoff frequency may vary depending on the animal model. The recommended 2Hz is for rabbits.
Add a Digital Filter by:
- Clicking on the Channel Menu (accessed by left-clicking the blue channel name label)
- Choose the Digital Filter option
- Select High Pass as the Filter Type
- Enter the Cutoff Frequency
The reason this low-frequency noise affected the placement of the end of the T wave is because the software looks for the point at which the waveform crosses back over the isoelectric line. When low-frequency noise is affecting the signal, the isoelectric line will be affected, as will the point at which the waveform crosses over. In some cases, the peak of the T wave might appear to be below the isoelectric line, which means the waveform will not cross over again during that heartbeat. This is a case in which the T end will not be marked in LabChart’s ECG Analysis Module. Adding the 2Hz High Pass Filter will ensure that the isoelectric line will be in the correct place because there will not be drift due to the breathing of the animal, while keeping the actual ECG signal intact.