ECG Educator Blog : Six Second ECG Rhythm Strips - Free Printable

The ECG shown in the image is labeled as "Normal Sinus Rhythm (NSR)" and is recorded from Lead II. Let's analyze it step-by-step to confirm this diagnosis and explain what makes it a normal sinus rhythm.

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🔍 ECG Interpretation: Step-by-Step

#### 1. Rate
- The heart rate is regular.
- To calculate the rate:
- Count the number of R waves in a 6-second strip (which is 30 large squares at 25 mm/sec).
- There are 6 R waves in this strip.
- So, 6 beats in 6 seconds = 60 beats per minute (bpm).
- Rate: ~60 bpm → within normal range (60–100 bpm).

✔ Normal sinus rate.

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#### 2. Rhythm
- The P waves are present before each QRS complex.
- P waves are regularly spaced, and the PP intervals are consistent.
- The RR intervals are also regular.

✔ Regular rhythm — consistent with sinus rhythm.

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#### 3. P Waves
- Each QRS complex is preceded by a P wave.
- The P waves are upright in Lead II (normal for Lead II).
- They have a consistent morphology and amplitude (not too tall or wide).
- This indicates that the impulse originates in the sinus node.

✔ Sinus P waves — normal.

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#### 4. PR Interval
- The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex.
- In this tracing, the PR interval is constant and approximately 0.16–0.20 seconds (about 3–4 small squares).
- Normal PR interval: 0.12–0.20 seconds.

✔ Normal PR interval.

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#### 5. QRS Complex
- The QRS complexes are narrow (less than 0.12 seconds), indicating supraventricular origin.
- Consistent shape and amplitude.
- No evidence of bundle branch block or ventricular conduction delay.

✔ Normal QRS morphology.

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#### 6. ST Segment & T Wave
- ST segments are isoelectric (flat, no elevation or depression).
- T waves are upright and proportional in size to the QRS complexes.
- No signs of ischemia, infarction, or electrolyte abnormalities.

✔ Normal repolarization.

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✔ Final Diagnosis: Normal Sinus Rhythm (NSR)

This ECG demonstrates:
- Regular rhythm
- Upright P waves before each QRS
- Normal PR interval
- Narrow QRS complexes
- Normal ST segments and T waves
- Heart rate of ~60 bpm

All criteria for Normal Sinus Rhythm are met.

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📌 Clinical Significance

Normal Sinus Rhythm means:
- The heart’s electrical impulse is generated by the sinus node.
- The atria and ventricles are depolarizing in a coordinated manner.
- It is the expected rhythm in healthy individuals at rest.

This ECG is diagnostically normal and does not indicate any arrhythmias, conduction blocks, or ischemic changes.

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🧠 Summary

| Feature | Finding | Normal? |
|---------------------|-----------------------------|--------|
| Rate | ~60 bpm | ✔ Yes |
| Rhythm | Regular | ✔ Yes |
| P waves | Present, upright, consistent| ✔ Yes |
| PR interval | Constant (~0.16–0.20 sec) | ✔ Yes |
| QRS duration | <0.12 sec | ✔ Yes |
| ST segment/T wave | Normal | ✔ Yes |

➡️ Conclusion: Normal Sinus Rhythm (NSR)

Let me know if you'd like help interpreting other leads or understanding how to measure intervals!