Components of an ECG and Their Functions

Front

P Wave

Back

Represents atrial depolarization. It occurs when the sinoatrial (SA) node generates an impulse, causing the atria to contract and pump blood into the ventricles.

Front

QRS Complex

Back

Represents ventricular depolarization. This is the electrical impulse traveling through the ventricles, causing them to contract. It also includes the repolarization of the atria, which is hidden within the QRS complex.

Front

Q wave

Back

The first negative deflection before the R wave.

Front

R wave

Back

The first positive deflection after the P wave.

Front

S wave

Back

The negative deflection that follows the R wave.

Front

T Wave

Back

Represents ventricular repolarization. After the ventricles contract and pump blood, the cells undergo repolarization to prepare for the next contraction.

Front

PR Interval

Back

Represents the time it takes for the electrical impulse to travel from the SA node to the AV node and then through the AV bundle to the ventricles. It includes the P wave and the PR segment. The PR interval reflects the delay at the AV node, allowing the ventricles time to fill with blood before they contract.

Front

ST Segment

Back

Represents the period between ventricular depolarization and ventricular repolarization. This segment is flat, showing that the ventricles are fully contracted and in a brief phase of no electrical activity between depolarization and repolarization.

Front

QT Interval

Back

Represents the total time for ventricular depolarization and ventricular repolarization. It measures the duration of the electrical events in the ventricles, from the start of the QRS complex to the end of the T wave.