What is the RR interval?

• A. The time from the start of one QRS complex to the start of the next QRS complex
• B. The interval between the P wave and the QRS complex
• C. The duration of the QT interval
• D. The time from the start of the QRS to the end of the T wave

Answer: (A)

The RR interval is the timing between successive ventricular activations seen on the ECG. It is the time from the start of one QRS complex to the start of the next QRS complex, which reflects how often the heartbeats occur. Shorter RR intervals mean a faster heart rate, while longer ones indicate a slower rate, and it’s useful for judging rhythm regularity. You can estimate heart rate from it with approximately 60 divided by the RR interval in seconds. The other options reference different intervals: the PR interval is from the start of the P wave to the start of the QRS and reflects AV conduction; the QT interval runs from the start of the QRS to the end of the T wave and covers ventricular depolarization to repolarization.