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← Theoretical A

Q38 — ECG Interpretation

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Cardiovascular Physiology

An electrocardiogram (ECG) records the heart’s electrical activity using electrodes on the skin. Leads I, II, and III form Einthoven’s triangle and provide key views of the heart’s electrical axis by measuring voltage differences between the limbs. Lead I measures between the right and left arms, Lead II between the right arm and left leg, and Lead III between the left arm and left leg. In modern diagnostic medicine, 12 leads are used for a more comprehensive analysis of the heart’s activity.

Einthoven’s triangle formed by ECG leads I, II, and III with a vector showing the heart’s mean electrical axis; a lead-II ECG trace with the P wave, QRS complex, and T wave labeled; and membrane potential traces from three different cardiomyocyte regions. Figure 1. A Leads I, II, and III form Einthoven’s triangle with red vectors showing the heart’s mean current direction and amplitude. B ECG measurements along lead II with P wave, QRS complex, and T wave. C Membrane potential of cardiomyocytes from different heart regions during the cardiac cycle.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Graph 2 in Figure 1C was registered in a cardiomyocyte from the sinoatrial node.
B. Full atrioventricular node blockade would result in only the P wave being visible.
C. The S wave represents repolarization.
D. The amplitude of the P wave in Figure 1A is larger in the lead II than in the lead III.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)