ECG Practical Content and Preparation 2 — Questions and Answers
Question 1: A patient's ECG shows a PR interval of 0.28 seconds with no dropped beats. Which condition does this represent?
- First-degree AV block (Correct answer)
- Second-degree AV block Mobitz I
- Second-degree AV block Mobitz II
- Third-degree AV block
Correct answer: First-degree AV block
First-degree AV block is defined by a PR interval >0.20 seconds with every P wave conducted to the ventricles.
Question 2: Which electrode placement error would most likely cause an artificially inverted P wave in lead II?
- Reversing the left arm and left leg electrodes
- Reversing the right arm and left arm electrodes (Correct answer)
- Placing the V1 electrode one intercostal space too high
- Reversing the right leg and left leg electrodes
Correct answer: Reversing the right arm and left arm electrodes
Swapping the right arm (RA) and left arm (LA) electrodes inverts leads I and aVL and reverses the polarity of lead II, causing an inverted P wave.
Question 3: When preparing a patient for a 12-lead ECG, the technician should instruct the patient to:
- Breathe deeply and rhythmically during recording
- Remain still and avoid talking (Correct answer)
- Flex the arm muscles to improve electrode contact
- Sit upright at a 90-degree angle
Correct answer: Remain still and avoid talking
Patient movement and speech introduce artifact, so the patient must remain still and quiet during the recording.
Question 4: On standard ECG paper running at 25 mm/sec, one large box (5 mm) represents which time interval?
- 0.04 seconds
- 0.10 seconds
- 0.20 seconds (Correct answer)
- 0.40 seconds
Correct answer: 0.20 seconds
At 25 mm/sec, each large box (5 mm) equals 0.20 seconds; each small box (1 mm) equals 0.04 seconds.
Question 5: Which finding on a rhythm strip most reliably confirms sinus rhythm?
- Regular R-R intervals
- QRS duration less than 0.12 seconds
- Positive P wave in lead II preceding each QRS (Correct answer)
- Heart rate between 60 and 100 bpm
Correct answer: Positive P wave in lead II preceding each QRS
Sinus rhythm requires that the SA node drive the heart, confirmed by an upright P wave in lead II before every QRS complex.
Question 6: A patient arrives for an ECG with lotion on the chest. The best immediate action is to:
- Apply extra electrode gel over the lotion
- Wipe the skin dry with a towel and apply electrodes
- Proceed with the ECG and note the artifact
- Clean the skin with an alcohol prep pad and allow it to dry (Correct answer)
Correct answer: Clean the skin with an alcohol prep pad and allow it to dry
Alcohol prep pads remove oils and lotion that impair electrode adhesion; allowing the skin to dry fully ensures good contact.
Question 7: The ST segment on an ECG represents which phase of cardiac electrical activity?
- Atrial depolarization
- Ventricular repolarization plateau (phase 2) (Correct answer)
- AV nodal conduction delay
- Ventricular depolarization
Correct answer: Ventricular repolarization plateau (phase 2)
The ST segment corresponds to the plateau phase of ventricular action potentials, during which all ventricular cells are depolarized.
ECG Practical Content and Preparation 2
A patient's ECG shows a PR interval of 0.28 seconds with no dropped beats.
Which condition does this represent?