A 52-year-old man undergoes a 12-lead ECG during routine health screening. Regarding the normal ECG findings and their electrophysiological basis, all of the following are true EXCEPT:

Question

Accepted Answer

A. The U wave, when visible, represents repolarization of the Purkinje system and atrial repolarization, and is typically seen in leads V2–V4. ## ECG Segments, Intervals, and Waves — Detailed Analysis

### U Wave — The Incorrect Statement

**Key Point:** The U wave represents repolarization of the **Purkinje system and ventricular muscle**, NOT atrial repolarization. Atrial repolarization occurs during ventricular depolarization (QRS complex) and is typically buried within and obscured by the QRS complex.

**High-Yield:** The U wave is a small deflection that follows the T wave and is best visualized in leads **V2–V4** (correct location in the option). However, its origin is Purkinje and ventricular muscle repolarization, not atrial repolarization. The U wave is often absent or small and becomes prominent in **hypokalemia**, **bradycardia**, and **prolonged QT interval**.

### Correct ECG Components

| Component | Duration/Measurement | Represents | Normal Features |
|-----------|----------------------|-----------|------------------|
| **ST segment** | Isoelectric or near-isoelectric | Plateau phase of ventricular action potential (entire ventricle depolarized) | Should be at baseline |
| **QT interval** | Measured QRS start to T wave end | Total ventricular depolarization + repolarization | QTc < 0.44 s (males); < 0.46 s (females) |
| **TP segment** | Baseline between T and P waves | Isoelectric reference line | Used for ST segment measurement |
| **U wave** | Small deflection after T wave | Purkinje + ventricular muscle repolarization | Best in V2–V4; absent in many normal individuals |

**Clinical Pearl:** Atrial repolarization (Ta wave) occurs during the QRS complex and is normally invisible because it is buried within the much larger QRS deflection. This is why we do not see a separate atrial repolarization wave on the normal ECG.

**Mnemonic:** **PQRSTU** — P (atrial depol), QRS (ventricular depol), T (ventricular repol), U (Purkinje repol). Remember: **U = Purkinje, NOT atria**.

Answer

B. The QT interval is measured from the beginning of the QRS complex to the end of the T wave and normally corrects to less than 0.44 seconds (QTc < 0.44 s) in males

Answer

C. The ST segment represents the period between the end of ventricular depolarization and the beginning of ventricular repolarization, during which the entire ventricle is depolarized

Answer

D. The TP segment (baseline between T wave and P wave) is used as the reference for isoelectric line measurement and ST segment elevation or depression

A 52-year-old man undergoes a 12-lead ECG during routine health screening. Regarding the normal ECG findings and their electrophysiological basis, all of the following are true EXCEPT:

Explanation

ECG Segments, Intervals, and Waves — Detailed Analysis

U Wave — The Incorrect Statement

Correct ECG Components

Practice similar questions

Join our NEET PG community

Component	Duration/Measurement	Represents	Normal Features
ST segment	Isoelectric or near-isoelectric	Plateau phase of ventricular action potential (entire ventricle depolarized)	Should be at baseline
QT interval	Measured QRS start to T wave end	Total ventricular depolarization + repolarization	QTc < 0.44 s (males); < 0.46 s (females)
TP segment	Baseline between T and P waves	Isoelectric reference line	Used for ST segment measurement
U wave	Small deflection after T wave	Purkinje + ventricular muscle repolarization	Best in V2–V4; absent in many normal individuals