CCS Cardiac Rhythm Interpretation & ECG Analysis

Question 1

What is the normal PR interval on a standard 12-lead ECG?

Accepted Answer

0.12–0.20 seconds

Answer

The normal PR interval is 0.12–0.20 seconds, representing the time for an impulse to travel from the SA node through the AV node to the ventricles.

Question 2

Which ECG finding is characteristic of first-degree AV block?

Accepted Answer

Consistently prolonged PR interval greater than 0.20 seconds with all P waves conducted

Answer

First-degree AV block is defined by a PR interval consistently >0.20 seconds, with every P wave still successfully conducted to the ventricles.

Question 3

What heart rate range defines sinus bradycardia in an adult?

Accepted Answer

Less than 60 bpm

Answer

Sinus bradycardia is defined as a sinus rhythm with a heart rate less than 60 beats per minute originating from the SA node.

Question 4

On a standard ECG, what physiologic event does the QRS complex represent?

Accepted Answer

Ventricular depolarization

Answer

The QRS complex represents ventricular depolarization, which triggers the mechanical contraction of both ventricles.

Question 5

What is the normal QRS duration on an ECG?

Accepted Answer

0.06–0.10 seconds

Answer

Normal QRS duration is 0.06–0.10 seconds (60–100 ms); a duration ≥0.12 seconds suggests a bundle branch block or ventricular origin.

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