The normal PR interval measurement is:
A) 0.06 to 0.12 second.
B) 0.20 to 0.24 second.
C) 0.12 to 0.20 second.
D) 0.10 to 0.16 second.
The normal range for the QRS complex duration is:
A) 0.12 to 0.20 second.
B) greater than 0.12 second.
C) 0.06 to 0.10 second.
D) less than 0.06 second.
The Correct Answer and Explanation is :
Correct Answers:
- The normal PR interval measurement is: C) 0.12 to 0.20 second.
- The normal range for the QRS complex duration is: C) 0.06 to 0.10 second.
Explanation:
1. PR Interval
The PR interval represents the time it takes for an electrical impulse to travel from the atria (through the AV node) to the ventricles. This interval includes atrial depolarization and the delay at the AV node, allowing time for the ventricles to fill with blood.
- Normal Range: 0.12 to 0.20 seconds (120–200 milliseconds).
- A PR interval shorter than 0.12 seconds suggests a pre-excitation syndrome (e.g., Wolff-Parkinson-White syndrome) or another conduction anomaly.
- A PR interval longer than 0.20 seconds is considered prolonged, indicating first-degree heart block or other conduction delays.
2. QRS Complex
The QRS complex reflects ventricular depolarization, the process by which the electrical impulse spreads through the ventricles, triggering their contraction. The duration of the QRS complex is determined by the speed of conduction through the ventricles.
- Normal Range: 0.06 to 0.10 seconds (60–100 milliseconds).
- A QRS duration greater than 0.10 seconds suggests abnormal ventricular conduction, such as bundle branch block or ventricular hypertrophy.
- A QRS duration greater than 0.12 seconds is indicative of a more significant conduction defect like a complete bundle branch block.
Clinical Importance:
Evaluating the PR interval and QRS duration is essential in diagnosing and monitoring heart conditions. Deviations from normal ranges can indicate electrical conduction abnormalities, ischemia, electrolyte imbalances, or structural heart disease. Interpreting these intervals in an ECG provides critical insights into a patient’s cardiac function.