CET Lead Placement & Recording Procedures 3 — Questions and Answers
Question 1: Which lead is considered the 'ground' or reference electrode in a standard 12-lead ECG setup?
- Right arm (RA)
- Left arm (LA)
- Right leg (RL) (Correct answer)
- Left leg (LL)
Correct answer: Right leg (RL)
The right leg (RL) electrode serves as the electrical ground or reference and does not contribute to any of the 12 leads.
Question 2: V4 is placed at the:
- Fifth intercostal space, left midclavicular line (Correct answer)
- Fourth intercostal space, left sternal border
- Fifth intercostal space, left anterior axillary line
- Sixth intercostal space, left midaxillary line
Correct answer: Fifth intercostal space, left midclavicular line
V4 is positioned at the fifth intercostal space at the midclavicular line, typically over the cardiac apex.
Question 3: When a technician notices AC (60 Hz) interference on the ECG tracing, the first corrective step should be:
- Increase the paper speed to 50 mm/sec
- Check and correct electrode connections and skin contact (Correct answer)
- Repeat the test in a different room immediately
- Apply a digital filter and proceed
Correct answer: Check and correct electrode connections and skin contact
AC interference usually results from poor electrode contact or nearby electrical equipment; checking connections and skin preparation resolves it without altering the signal.
Question 4: In right-sided ECG leads (V3R–V6R), where is V4R placed?
- Mirror image of V4 on the right chest at the fifth ICS, right midclavicular line (Correct answer)
- Fourth ICS, right sternal border
- Fifth ICS, right anterior axillary line
- Same position as standard V4
Correct answer: Mirror image of V4 on the right chest at the fifth ICS, right midclavicular line
V4R is the right-side mirror of V4, placed at the fifth intercostal space on the right midclavicular line, critical for detecting right ventricular MI.
Question 5: A patient's left arm is in a cast. Which adjustment is appropriate for the LA electrode?
- Place the LA electrode on the left shoulder
- Omit the LA electrode entirely
- Place the LA electrode on the right arm instead
- Place the LA electrode as high on the left arm as possible above the cast (Correct answer)
Correct answer: Place the LA electrode as high on the left arm as possible above the cast
The electrode should be placed on the most distal accessible portion of the same limb to maintain anatomical consistency of the limb lead system.
Question 6: The sensitivity (gain) setting of 10 mm/mV means:
- 1 mV of cardiac signal produces a 10 mm deflection on the ECG paper (Correct answer)
- 10 mV produces a 1 mm deflection
- The paper speed is set to 10 mm/sec
- The filter is set to 10 Hz
Correct answer: 1 mV of cardiac signal produces a 10 mm deflection on the ECG paper
Standard sensitivity is 10 mm/mV, so a 1 mV calibration pulse deflects the stylus exactly 10 mm (two large squares).
Question 7: Which of the following is the correct sequence for placing precordial leads from V1 to V6?
- Right sternal border → Left sternal border → Between V2 and V4 → Midclavicular → Anterior axillary → Midaxillary (Correct answer)
- Apex → Right sternal → Left sternal → Midclavicular → Anterior axillary → Midaxillary
- Left sternal border → Right sternal border → Midclavicular → Between V2 and V4 → Anterior axillary → Midaxillary
- Midaxillary → Anterior axillary → Midclavicular → Between V2 and V4 → Left sternal → Right sternal
Correct answer: Right sternal border → Left sternal border → Between V2 and V4 → Midclavicular → Anterior axillary → Midaxillary
V1 (right sternal 4th ICS) → V2 (left sternal 4th ICS) → V3 (between V2 and V4) → V4 (5th ICS midclavicular) → V5 (anterior axillary) → V6 (midaxillary, same level as V4/V5).
CET Lead Placement & Recording Procedures 3
Which lead is considered the 'ground' or reference electrode in a standard 12-lead ECG setup?