ECG Practical Content and Preparation 4

Question 1

Right bundle branch block (RBBB) is classically identified by which pattern in lead V1?

Accepted Answer

RSR' (rabbit ear) pattern

Answer

RBBB produces a characteristic RSR' (M-shaped or 'rabbit ear') pattern in V1 with a QRS duration ≥0.12 seconds.

Question 2

Which lead best visualizes the inferior wall of the left ventricle?

Accepted Answer

Leads II, III, and aVF

Answer

Leads II, III, and aVF face the inferior surface of the left ventricle and detect changes associated with inferior MI.

Question 3

A patient's ECG shows P waves at 85 bpm with a QRS rate of 35 bpm, and no consistent PR interval. This finding is consistent with:

Accepted Answer

Complete (third-degree) AV block

Answer

Complete (third-degree) AV block means the atria and ventricles fire independently with no relationship between P waves and QRS complexes.

Question 4

Which ECG change is the earliest and most sensitive indicator of acute hyperkalemia?

Accepted Answer

Tall, peaked (tented) T waves

Answer

Tall, narrow, peaked T waves are the earliest ECG manifestation of hyperkalemia, appearing when serum potassium rises above ~5.5 mEq/L.

Question 5

For a patient with a heart rate of 150 bpm on a rhythm strip at 25 mm/sec, the R-R interval measures approximately how many large boxes?

Accepted Answer

2 large boxes

Answer

At 25 mm/sec, 300 ÷ 150 bpm = 2 large boxes per R-R interval (the '300 method').

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