What is the heart rate in the given ECG graph?& x20;

NORCET 8 Prelims-2025

Medical & Surgical Nursing

Medium

What is the heart rate in the given ECG graph?

Appeared in: NORCET 8 Prelims-2025

The heart rate is calculated using the '300 method' for regular rhythms, where 300 is divided by the number of large squares between two consecutive R waves.
In the given ECG, the R-R interval (the distance between the peaks of two consecutive QRS complexes) is consistently 3 large squares.
Applying the formula: Heart Rate = 300 / 3 = 100 beats per minute (bpm).
This indicates a normal sinus rhythm, as a rate 100 bpm is for an adult at rest.

Option A : A heart rate of 75 bpm would mean there are exactly 4 large squares between R waves (300 / 4 = 75 The ECG shows 4 squares.
Option C: A heart rate of 150 bpm would mean there are exactly 2 large squares between R waves (300 / 2 = 150). The ECG shows 4 squares.
Option D: A heart rate of 300 bpm would mean there is exactly 1 large square between R waves (300 / 1 = 300). The ECG shows 4 squares.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain ECG Interpretation: Heart Rate Calculation as background academic context rather than a clinical decision trigger.
Accurate heart rate calculation is a fundamental nursing skill for identifying arrhythmias. A rate below 60 bpm is bradycardia, and a rate above 100 bpm is tachycardia. Both may require intervention.
Prompt identification of an abnormal heart rate allows the nurse to assess the patient for symptoms (e.g., dizziness, shortness of breath, palpitations), check vital signs, and notify the healthcare provider for further orders.
The '300 method' is a quick and reliable tool at the bedside for regular rhythms, but it is inaccurate for irregular rhythms. Nurses must first assess rhythm regularity before choosing a calculation method.

How to Approach the Question

.First, analyze the question. It asks for the heart rate from a provided ECG graph.

Examine the ECG strip to determine if the rhythm is regular or irregular. Look at the spacing between the R waves (the tall peaks). In this case, the spacing is consistent, so the rhythm is regular.
For a regular rhythm, recall the '300 method' (or 'large box method') for a quick calculation. This is the most common and fastest method for exams.
Select an R wave that falls on a heavy grid line. Count the number of large squares until the next R wave.
Divide 300 by the number of large squares you counted. Here, it's 300 / 3= 100
Compare your calculated rate with the given options and select the matching one.

Concept Tested & Keywords

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

E6 Medicine Harrison 22e Part 1 p. 1909-1911

Practise the full NORCET 8 Prelims-2025

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