An ECG strip is shown. Calculate the heart rate.

Appeared in: NORCET 10 Prelims-2026

Explanation

The most accurate method for calculating the heart rate from a regular ECG rhythm is the 1500 method.
This involves counting the number of small 1-mm squares between two consecutive R-waves (the R-R interval).
In the provided ECG, there are approximately 36 small squares between the R-waves.
The heart rate is calculated by dividing 1500 by the number of small squares: 1500 / 36 = 41.67.
Rounding this value to the nearest whole number gives a heart rate of 42 beats per minute (bpm).

Option B: A heart rate of 45 bpm would correspond to an R-R interval of approximately 33 small squares (1500 / 45 ≈ 33.3), which is not consistent with the ECG strip shown.
Option C: A heart rate of 50 bpm would correspond to an R-R interval of exactly 30 small squares (1500 / 50 = 30). The interval in the image is visibly wider than 30 squares (6 large squares).
Option D: A heart rate of 38 bpm would correspond to an R-R interval of approximately 39-40 small squares (1500 / 38 ≈ 39.5). The interval in the image is slightly shorter than this.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain ECG Interpretation and Heart Rate Calculation as background academic context rather than a clinical decision trigger.
Accurate heart rate calculation is a fundamental nursing skill for assessing cardiac function and identifying potentially life-threatening arrhythmias like severe bradycardia or tachycardia.
The calculated rate of 42 bpm is sinus bradycardia. A nurse must assess the patient for symptoms like dizziness, syncope, or shortness of breath and check their medication list for drugs that can lower heart rate (e.g., beta-blockers, digoxin).
What if the rhythm was irregular? The 1500 and 300 methods would be inaccurate. The nurse must use the 6-second strip method (count R-waves in a 6-second strip and multiply by 10) for a reliable average heart rate.

How to Approach the Question

First, identify the core task, which is to calculate the heart rate from a provided ECG image.
Analyze the ECG strip to determine if the rhythm is regular or irregular by checking if the R-R intervals are consistent.
For a regular rhythm, select the most accurate calculation method, which is the 1500 (small square) method.
Carefully count the number of small squares between two consecutive R-waves.
Divide 1500 by the number of small squares you counted.
Compare your calculated result with the given options to find the closest match.

Concept Tested & Keywords

Q6MVNwQuPWTmfH_SZrPP5u

E6 Medicine Davidson Principles Practice 24e p. 468-470

E6 Medicine Macleod Clinical Examination 15e p. 60-62

E6 Nursing Vital Signs p. 79-81

Practise the full NORCET 10 Prelims-2026

Attempt every question from this paper in a timed mock, then review the full solution for each one.