The cardiac artefact in the BIS EEG¶
The BIS EEG carries a weak electrical trace of every heartbeat. Too weak for beat-by-beat matching, it shows clearly when averaged on the ECG's R peaks, and gives a second SNUADC–BIS timing reference that agrees with the bursts to about 16 ms.
| Date | 2026-10-12 |
| Status | current |
| Methods | One event, two clocks |
| Techniques | Null controls |
| Clocks | BIS clock, SNUADC sample clock |
| Devices | BIS monitor, SNUADC |
| Variables | BIS EEG, ECG lead II (SNUADC) |
Background¶
Heartbeat interval matching aligns EEG with ECG when the EEG carries the heartbeat (Goodwin et al. 2023). A first attempt found no usable heartbeat in the BIS EEG; it searched −0.3 to +0.5 s around each R peak on raw stamps, while the same event is stamped about 0.8 s earlier in BIS.
Data¶
30 benchmark cases with BIS (a first attempt on 28), three 10-minute windows per channel each.
Method¶
Both devices on stamp-model time; R-triggered averages of the EEG from −2 to +1 s, in three 10-minute windows per channel per case; the peak lag compared with the burst-measured offset.
Results¶
- A clear peak (peak-to-noise ≥ 8) in 44 of 180 windows, in 13 of 30 cases; weaker peaks at the same lag in many more. Median amplitude 4.3 µV.
- Its lag matches the burst offset to a median of −16 ms (p10–p90 −31 to +9 ms): electrical, near-simultaneous with the R wave.
- Single beats are too weak: single-beat SNR 0.4 median, so beat-by-beat interval matching stays impractical.
Discussion¶
The averaged artefact is a second, independent SNUADC–BIS reference, including in cases with no bursts. It supersedes the first attempt's conclusion that the BIS EEG carries no heartbeat.
Observations it supports¶
| Observation | Status | Summary |
|---|---|---|
| The BIS EEG carries an averaged cardiac artefact | likely | Averaged on the ECG's R peaks, the BIS EEG shows the heartbeat (median 4.3 µV), near-simultaneous with the R wave. Single beats are too weak to match one by one. |
Open questions¶
- Why the artefact shows in only some cases (unexplained phenomenon). A clear averaged artefact appears in 13 of 30 cases. What decides whether it is visible (electrode placement, signal quality, filtering) is not known.
Code¶
References¶
- Goodwin AJ, Dixon W, Mazwi M, Hahn CD, Meir T, Goodfellow SD, Kazazian V, Greer RW, McEwan A, Laussen PC, et al. The truth Hertz – synchronization of electroencephalogram signals with physiological waveforms recorded in an intensive care unit. Physiol Meas. 2023;44(8):085002. ↗