Interpret an EKG
Read the P wave, QRS complex, and T wave on an EKG and connect each one to an electrical event in the heart.
- Atria vs. ventricles: The EKG separates atrial events from ventricular events, so you must know which chambers are which.
- Electrical signal triggers contraction: An EKG records electrical activity; knowing the signal comes before the squeeze explains why the waves line up with the heartbeat.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
A normal EKG has three features in order: the P wave (atrial depolarization), the QRS complex (ventricular depolarization), and the T wave (ventricular repolarization).
On the EKG tracing shown, which lettered feature marks ventricular depolarization (the ventricles being triggered to contract)?
Reviewed- A.A, the first small bump
- B.B, the tall narrow spike
- C.C, the wide rounded bump
- D.None: depolarization does not appear on an EKG
Show the worked solution ▾
Answer: B. B, the tall narrow spike
- Step 1: Match each feature to its event: The small first bump (A) is the P wave; the tall spike (B) is the QRS complex; the wide later bump (C) is the T wave.
- Step 2: Find ventricular depolarization: Ventricular depolarization is the QRS complex: the tall spike: because the large ventricles produce a big signal as they are triggered to contract.
Why it's right: The tall, narrow spike (B) is the QRS complex, which records ventricular depolarization as the ventricles are triggered to contract.
- A: A is the P wave, which marks atrial depolarization, not ventricular.
- C: C is the T wave, which marks ventricular repolarization (the reset), not depolarization.
- D: Depolarization is exactly what the EKG records; it does appear, as the P wave and QRS complex.
Aligned to HBS 3.1: P wave, QRS, T wave · reading level ~grade 9
- A clinician scanning a rhythm strip checks that every QRS spike is preceded by a P wave to confirm the signal is starting in the atria.
Fill these in as you work through the lesson.
- EKG (ECG) (a tracing of the heart's electrical signals):
- Depolarization (the electrical change that triggers a chamber to contract):
- Repolarization (the electrical reset of a chamber):
- P wave (first small bump on the tracing):
- QRS complex (the tall spike):
- T wave (the rounded bump after the spike):
On an EKG the wave shows atrial depolarization, the complex shows ventricular depolarization, and the wave shows ventricular repolarization.
- Which wave comes first on a normal EKG, and what is the heart doing then?
- Why is the QRS complex larger than the P wave?
- What electrical event does the T wave record?
Given an EKG strip showing a P wave, then a tall spike, then a rounded bump, label each feature and name the electrical event it represents.