What is the P-R interval in an ECG?

What is the P-R interval in an ECG?

• A. The time from atrial depolarization (P wave) to ventricular depolarization (QRS complex).
• B. The duration of the QRS complex.
• C. The time from ventricular depolarization to ventricular repolarization.
• D. The time from atrial repolarization to ventricle repolarization.

Answer: (A)

The P-R interval reflects the time it takes for the electrical signal to travel from the atria to the ventricles. It starts at the beginning of the P wave, which shows atrial depolarization, and ends at the start of the QRS complex, which marks ventricular depolarization. This interval therefore represents conduction through the AV node and the His-Purkinje system before the ventricles begin to depolarize. Normal duration is about 0.12 to 0.20 seconds. If it’s longer, AV nodal delay or a block may be present; if shorter, there may be pre-excitation via an accessory pathway. The other options describe different things: the duration of the QRS is ventricular depolarization alone; the interval from ventricular depolarization to repolarization is the QT interval; and the idea of atrial repolarization to ventricular repolarization isn’t a standard, defined interval.

The P-R interval reflects the time it takes for the electrical signal to travel from the atria to the ventricles. It starts at the beginning of the P wave, which shows atrial depolarization, and ends at the start of the QRS complex, which marks ventricular depolarization. This interval therefore represents conduction through the AV node and the His-Purkinje system before the ventricles begin to depolarize. Normal duration is about 0.12 to 0.20 seconds. If it’s longer, AV nodal delay or a block may be present; if shorter, there may be pre-excitation via an accessory pathway. The other options describe different things: the duration of the QRS is ventricular depolarization alone; the interval from ventricular depolarization to repolarization is the QT interval; and the idea of atrial repolarization to ventricular repolarization isn’t a standard, defined interval.