CET ECG Equipment Operation & Maintenance 3 — Questions and Answers
Question 1: A 60 Hz interference pattern on an ECG tracing most commonly indicates which problem?
- Patient movement artifact
- Poor electrode-to-skin contact or AC electrical interference (Correct answer)
- Incorrect paper speed setting
- Damaged stylus heating element
Correct answer: Poor electrode-to-skin contact or AC electrical interference
60 Hz (AC) interference appears as a rapid, regular oscillation on the baseline and is typically caused by poor electrode contact or nearby electrical devices.
Question 2: Which lead configuration uses the left arm electrode as the positive terminal and the right arm as the negative terminal?
- Lead I (Correct answer)
- Lead II
- Lead III
- aVR
Correct answer: Lead I
Lead I measures the potential difference from right arm (negative) to left arm (positive), reflecting lateral heart activity.
Question 3: What is the primary reason disposable adhesive ECG electrodes have a defined expiration date?
- The conductive gel dries out, increasing impedance and reducing signal quality (Correct answer)
- The plastic backing degrades and becomes electrically active
- The color coding fades, causing placement errors
- The adhesive becomes too strong and may injure skin
Correct answer: The conductive gel dries out, increasing impedance and reducing signal quality
Expired electrodes have dehydrated gel that increases skin-electrode impedance, producing poor signal quality and artifact.
Question 4: During a 12-lead ECG, the technician observes that aVR, aVL, and aVF all show artifact but limb leads I, II, and III are clean. What is the most likely cause?
- A broken internal circuit in the ECG machine
- A faulty right leg (ground) electrode connection (Correct answer)
- Movement artifact from the patient
- Incorrect paper speed selected
Correct answer: A faulty right leg (ground) electrode connection
The augmented leads (aVR, aVL, aVF) are derived differently than the bipolar leads; a faulty ground (RL) electrode selectively corrupts them while bipolar leads may appear relatively clean.
Question 5: What thermal paper storage condition will cause premature darkening or degradation of ECG paper?
- Storing at room temperature in a sealed box
- Storing in a cool, dry environment away from light
- Exposure to heat, humidity, or direct sunlight (Correct answer)
- Storing in a climate-controlled cabinet
Correct answer: Exposure to heat, humidity, or direct sunlight
Thermal paper is heat-sensitive; exposure to heat, humidity, or UV light causes premature darkening and makes tracings unreadable.
Question 6: Which ECG machine filter setting is most appropriate to reduce baseline wander caused by patient breathing?
- High-pass (low-frequency) filter set at 0.05 Hz or higher (Correct answer)
- Low-pass filter set at 40 Hz
- Notch filter at 60 Hz
- High-frequency filter set at 150 Hz
Correct answer: High-pass (low-frequency) filter set at 0.05 Hz or higher
A high-pass filter removes low-frequency drift (like respiratory baseline wander) while preserving the higher-frequency ECG signal components.
Question 7: When preparing a patient's skin for ECG electrode placement, what is the correct order of skin preparation steps?
- Apply electrode → clip hair → clean skin → dry skin
- Clip hair → clean skin with alcohol → dry skin → apply electrode (Correct answer)
- Clean skin → apply electrode → clip hair → dry skin
- Dry skin → clip hair → apply electrode → clean skin
Correct answer: Clip hair → clean skin with alcohol → dry skin → apply electrode
Proper sequence is: clip excess hair, clean with alcohol to remove oils/dead skin, dry thoroughly, then apply electrode for optimal adhesion and conductivity.
CET ECG Equipment Operation & Maintenance 3
A 60 Hz interference pattern on an ECG tracing most commonly indicates which problem?