ECG rhythm strip interpretationEasy
Measure the QRS duration on this lead II strip, in seconds.
lead II, 25 mm/s, 10 mm/mV1 small box = 0.04 s, 1 large box = 0.20 sstrip length 6 s
Find QRS (s)
Show hints
- The QRS starts where the trace leaves the baseline after the PR segment (the first deflection, Q or R).
- It ends at the J point, where the S wave returns to the baseline.
- The QRS is 2 small boxes wide.
Show the answer and the step-by-step solution
Reading the paper: ECG paper runs at 25 mm/s, so one small box (1 mm) is 0.04 s and one large box (5 mm) is 0.20 s; vertically 10 mm is 1 mV. For a regular rhythm the heart rate is 300 ÷ the number of large boxes between two R waves, or 1500 ÷ the number of small boxes (more exact). For an irregular rhythm count the QRS complexes in a 6-second strip and multiply by 10. Textbook normal values: PR interval 0.12–0.20 s (3–5 small boxes) from the start of the P wave to the start of the QRS; QRS duration below 0.12 s (under 3 small boxes); a rhythm is regular when the R–R intervals are the same.
Measure
2 small boxes from the start of the QRS to the J point
Convert
QRS = 2 × 0.04 s = 0.08 s
Answer
QRS = 0.08 s
Below 0.12 s: a narrow QRS, normal conduction through the ventricles.