Intraoperative ECG monitoring is being configured for continuous ST-segment analysis to detect myocardial ischaemia. Which statement about the monitor's filter settings is correct?

• A Monitoring mode filters are preferred for ST analysis because they remove baseline wander without altering the ST segment
• B Diagnostic mode filters attenuate muscle artefact more effectively than monitoring filters
• C Filter choice affects QRS detection but never the amplitude or morphology of the ST segment
• D Diagnostic mode filtering preserves the ST segment faithfully, whereas monitoring mode filters can distort ST elevation or depression ✓

Explanation

Diagnostic mode applies minimal filtering, preserving genuine ST-segment elevation or depression, while monitoring mode uses stronger high-pass and low-pass filtering to suppress baseline wander and muscle artefact. This aggressive filtering can distort ST amplitude and morphology, potentially masking or mimicking ischaemia. Therefore ST trend analysis requires the diagnostic filter setting, accepting more artefact in exchange for signal fidelity.

Reference: Miller's Anesthesia, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.