What may cause a strong ECG artifact in an EMG channel?

In the context of EMG (electromyography) channels, strong ECG (electrocardiogram) artifacts can indeed arise from high electrode impedances and poor electrode placement. When electrode impedances are high, this can lead to increased noise and interference in the EMG signal because the electrodes aren't effectively capturing the electrical activity from the muscle, leading to greater susceptibility to contamination from nearby electrical signals, such as those from the heart.

Similarly, poor electrode placement can contribute to similar issues. If electrodes are not placed correctly according to standard protocols, they may pick up unwanted signals from adjacent areas, including the heart's electrical activity. Proper placement is crucial for ensuring that the EMG accurately reflects muscular activity without interference from other bodily electrical signals.

The third option mentions that strong artifacts might be unavoidable due to bipolar EMG derivations; while bipolar configurations do have inherent challenges, the main contributors to ECG artifacts are largely related to electrode impedance and placement. Therefore, the combination of high electrode impedances and poor placement being identified as causes makes the correct answer clear.