CRAT ECG Waveform Measurements and Intervals 2 — Questions and Answers
Question 1: The ST segment on the ECG represents:
- Atrial depolarization
- AV node conduction delay
- The period between ventricular depolarization and repolarization (Correct answer)
- Ventricular filling time
Correct answer: The period between ventricular depolarization and repolarization
The ST segment represents the early phase of ventricular repolarization and is evaluated for elevation or depression suggesting ischemia or injury.
Question 2: Which calculation method uses the number of large squares between two R waves to estimate heart rate?
- 300 divided by number of large squares (Correct answer)
- 1500 divided by number of small squares
- 600 divided by number of large squares
- 60 divided by R-R interval in seconds
Correct answer: 300 divided by number of large squares
The '300 rule' divides 300 by the number of large squares between two consecutive R waves to estimate heart rate quickly.
Question 3: What does a delta wave at the onset of the QRS complex suggest?
- Right bundle branch block
- Pre-excitation syndrome (e.g., WPW) (Correct answer)
- Hyperkalemia
- Left ventricular hypertrophy
Correct answer: Pre-excitation syndrome (e.g., WPW)
A delta wave — a slurred upstroke at the start of the QRS — indicates pre-excitation of the ventricles via an accessory pathway, as seen in Wolff-Parkinson-White syndrome.
Question 4: An isoelectric baseline on the ECG refers to:
- A flat line indicating cardiac arrest
- The normal baseline between waveforms with no electrical activity (Correct answer)
- Prolonged asystole
- Pacemaker spike artifact
Correct answer: The normal baseline between waveforms with no electrical activity
The isoelectric line is the flat baseline between ECG waveforms, representing zero electrical potential and used as the reference point for ST segment analysis.
Question 5: The normal amplitude (height) of the R wave in lead II is typically:
- Less than 1 mm
- 5–25 mm (Correct answer)
- Greater than 35 mm
- Equal in all leads
Correct answer: 5–25 mm
In most leads, a normal R wave measures 5–25 mm; excessively tall R waves may indicate ventricular hypertrophy.
Question 6: Which interval is most commonly used to assess AV conduction time?
- QT interval
- PR interval (Correct answer)
- RR interval
- ST segment duration
Correct answer: PR interval
The PR interval reflects the time for impulse conduction from the SA node through the atria and AV node to the ventricles.
CRAT ECG Waveform Measurements and Intervals 2
The ST segment on the ECG represents: