ECG ECG Waveform Measurements and Intervals

Question 1

What is the normal duration of the PR interval in adults?

Accepted Answer

0.12–0.20 seconds

Answer

The normal PR interval is 0.12–0.20 seconds (3–5 small squares at 25 mm/sec), representing conduction time from the SA node through the AV node.

Question 2

The QRS complex normally has a duration of:

Accepted Answer

0.06–0.10 seconds

Answer

A normal QRS duration is 0.06–0.10 seconds; values ≥0.12 seconds indicate intraventricular conduction delay such as bundle branch block.

Question 3

The QT interval represents:

Accepted Answer

Total ventricular depolarization and repolarization

Answer

The QT interval spans from the start of the QRS to the end of the T-wave, encompassing all of ventricular electrical activity (depolarization and repolarization).

Question 4

A corrected QT interval (QTc) is calculated to account for:

Accepted Answer

Heart rate variation

Answer

QT interval lengthens at slower heart rates and shortens at faster rates; the QTc corrects for this, allowing comparison across different heart rates using Bazett's formula.

Question 5

What does a prolonged QTc interval (>500 ms) indicate clinically?

Accepted Answer

Increased risk of torsades de pointes ventricular tachycardia

Answer

A QTc >500 ms significantly increases the risk of torsades de pointes, a potentially fatal polymorphic ventricular tachycardia.

ECG (Electrocardiogram) Practice Test

ECG (Electrocardiogram) Practice Test

ECG ECG Waveform Measurements and Intervals