What is the normal range for the PR interval and what does prolongation indicate?

What is the normal range for the PR interval and what does prolongation indicate?

• A. 0.08–0.12 seconds
• B. 0.12–0.20 seconds
• C. 0.20–0.30 seconds
• D. 0.04–0.10 seconds

Answer: (B)

The PR interval measures the time from the start of atrial depolarization to the start of ventricular depolarization, reflecting conduction through the AV node. In a normal adult, this interval is 0.12 to 0.20 seconds. If it becomes longer than 0.20 seconds, that prolongation indicates slowed conduction through the AV node, most consistent with first-degree AV block. This slowing can result from factors like increased vagal tone, AV nodal blocking medications (such as certain beta-blockers or calcium channel blockers), electrolyte disturbances, ischemia or infarction involving the conduction system, or age-related degeneration of the conduction pathways. Shorter intervals (less than 0.12 seconds) are not considered prolongation and can be seen with rapid conduction or pre-excitation scenarios, while intervals longer than about 0.20 to 0.30 seconds reflect more significant AV conduction delay.

The PR interval measures the time from the start of atrial depolarization to the start of ventricular depolarization, reflecting conduction through the AV node. In a normal adult, this interval is 0.12 to 0.20 seconds. If it becomes longer than 0.20 seconds, that prolongation indicates slowed conduction through the AV node, most consistent with first-degree AV block. This slowing can result from factors like increased vagal tone, AV nodal blocking medications (such as certain beta-blockers or calcium channel blockers), electrolyte disturbances, ischemia or infarction involving the conduction system, or age-related degeneration of the conduction pathways. Shorter intervals (less than 0.12 seconds) are not considered prolongation and can be seen with rapid conduction or pre-excitation scenarios, while intervals longer than about 0.20 to 0.30 seconds reflect more significant AV conduction delay.