In a standard 12-lead ECG, which of the following represents the normal duration of the QRS complex?

Question

Accepted Answer

A. 0.08 to 0.12 seconds. ## Normal QRS Duration

**Key Point:** The QRS complex represents ventricular depolarization and normally lasts between 0.08 and 0.12 seconds (80–120 milliseconds) on a standard ECG.

### Measurement Method
- Count small squares on ECG paper: each small square = 0.04 seconds
- Normal QRS = 2–3 small squares in width
- Measured from the beginning of the Q wave (or R wave if no Q present) to the end of the S wave

### Clinical Significance

| Duration | Interpretation | Clinical Significance |
|----------|-----------------|----------------------|
| < 0.08 s | Narrow QRS | Normal ventricular conduction |
| 0.08–0.12 s | **Normal range** | **Standard reference** |
| 0.12–0.20 s | Prolonged QRS | Ventricular conduction delay (RBBB, LBBB, hyperkalemia) |
| > 0.20 s | Severely prolonged | Severe conduction abnormality or artifact |

**High-Yield:** A QRS duration ≥ 0.12 seconds (≥ 3 small squares) is diagnostic of bundle branch block and is a key criterion in NEET PG ECG questions.

**Clinical Pearl:** Prolonged QRS (> 0.12 s) increases risk of sudden cardiac death and is a criterion for cardiac resynchronization therapy (CRT) eligibility in heart failure patients.

![ECG Interpretation Basics diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3177.webp)

Answer

B. Less than 0.08 seconds

Answer

C. Greater than 0.20 seconds

Answer

D. 0.12 to 0.20 seconds

In a standard 12-lead ECG, which of the following represents the normal duration of the QRS complex?

Explanation

Normal QRS Duration

Measurement Method

Clinical Significance

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Duration	Interpretation	Clinical Significance
< 0.08 s	Narrow QRS	Normal ventricular conduction
0.08–0.12 s	Normal range	Standard reference
0.12–0.20 s	Prolonged QRS	Ventricular conduction delay (RBBB, LBBB, hyperkalemia)
> 0.20 s	Severely prolonged	Severe conduction abnormality or artifact