CRAT ECG Troubleshooting and Artifacts 2 — Questions and Answers
Question 1: Sixty-cycle (60 Hz) interference on an ECG most likely results from which cause?
- Nearby electrical equipment or poor electrode grounding (Correct answer)
- Patient movement
- Loose electrode gel
- Incorrect lead placement
Correct answer: Nearby electrical equipment or poor electrode grounding
60 Hz artifact appears as a thick, fuzzy baseline caused by electromagnetic interference from AC power sources including nearby electrical equipment or inadequate grounding.
AC interference produces a regular fine oscillation at exactly 60 Hz (60 small waves per second), making the baseline appear thickened. Solutions include moving equipment away from the patient, ensuring proper grounding, checking electrode connections, and asking the patient to lie still away from metal bed rails or IV pumps.
Question 2: Baseline wander on an ECG is most commonly caused by which factor?
- Patient breathing or movement causing electrode-skin interface changes (Correct answer)
- Electrical interference from AC current
- Incorrect paper speed
- Low battery in the ECG machine
Correct answer: Patient breathing or movement causing electrode-skin interface changes
Baseline wander results from slow undulation of the baseline caused by patient movement, respiration, poor electrode contact, or electrode gel drying.
Baseline wander produces slow, undulating movement of the ECG baseline at respiratory frequency. It occurs when electrode impedance changes during breathing or movement. It can mimic ST changes if severe. Solutions include proper skin preparation, fresh electrode gel, asking the patient to breathe shallowly, and ensuring electrode placement away from high-motion areas.
Question 3: A patient's ECG shows a completely flat line in lead II only, while other leads record normally. The most likely cause is which of the following?
- Disconnected or failed lead II electrode (Correct answer)
- Asystole
- Pacemaker failure
- Electrode misplacement on both limbs
Correct answer: Disconnected or failed lead II electrode
A flat line in one lead only, while other leads continue to show cardiac activity, indicates a technical failure specific to that lead — most likely a disconnected electrode.
True asystole produces isoelectric lines in all leads. A single flat lead with normal activity in others indicates a lead-specific technical problem: disconnected electrode, broken lead wire, poor skin contact, or a fallen electrode. Before any clinical intervention, always verify leads are connected and signals are present in multiple leads.
Question 4: Which action is most appropriate when a patient's ECG shows muscle tremor artifact that obscures rhythm interpretation?
- Reposition the electrodes away from muscle-heavy areas and ask the patient to relax (Correct answer)
- Increase the gain setting on the ECG machine
- Apply additional electrodes to all limbs
- Immediately interpret the rhythm despite artifact
Correct answer: Reposition the electrodes away from muscle-heavy areas and ask the patient to relax
Muscle tremor creates irregular high-frequency artifact that can mimic arrhythmias. Repositioning electrodes to bony prominences and asking the patient to relax reduces this artifact.
Skeletal muscle tremor produces irregular, rapid artifact that can resemble atrial fibrillation or ventricular fibrillation on the ECG. Solutions include placing limb electrodes over bony areas (wrists, ankles), ensuring patient comfort and warmth (Parkinson's tremor, shivering), and using the filter settings appropriately. Never diagnose a serious arrhythmia without first eliminating artifact.
Question 5: If limb leads show reversed arm electrode placement (right and left arm switched), which lead will appear inverted compared to a correct recording?
- Lead I (Correct answer)
- Lead V1
- Lead aVF
- Lead II
Correct answer: Lead I
Lead I measures the potential difference between the left arm (positive) and right arm (negative). Switching these electrodes inverts lead I and swaps leads II and III.
When right and left arm electrodes are reversed, lead I (LA-RA) becomes inverted. Lead II and lead III effectively swap. aVR and aVL swap. aVF is unaffected because it references the foot. A classic clue is a deeply negative P wave in lead I with a positive P in aVR, suggesting arm electrode reversal rather than true ectopic atrial rhythm.
Question 6: Which ECG parameter should be verified first when the paper tracing appears abnormally large or small for all waveforms?
- Calibration/gain setting (should show 10 mm/mV deflection) (Correct answer)
- Paper speed setting
- Lead selection
- Filter settings
Correct answer: Calibration/gain setting (should show 10 mm/mV deflection)
Standard ECG calibration is 10 mm per millivolt. If all waveforms are too large or too small, the gain (calibration) setting has been changed from the standard.
Standard ECG calibration produces a 10 mm tall (2 large boxes) rectangular calibration pulse at 1 mV. If the gain is doubled (20 mm/mV), all waveforms appear twice as tall. If halved (5 mm/mV), they appear smaller. Always document the calibration when recording, especially at non-standard settings, to avoid misinterpreting voltage criteria for hypertrophy or low voltage.
CRAT ECG Troubleshooting and Artifacts 2
Sixty-cycle (60 Hz) interference on an ECG most likely results from which cause?