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Electrocardiogram Pathology Quiz
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Which ECG feature is most characteristic of a ventricular ectopic beat?
- A Prolonged PR interval with otherwise normal P waves and QRS complexes You picked ✕
- B Broad QRS complex occurring early without a preceding P wave You picked ✓
- C Inverted P wave that may be hidden within a normal QRS complex You picked ✕
- D Abnormally shaped P wave appearing early followed by a normal QRS complex You picked ✕
- E Irregularly irregular rhythm caused by multiple atrial foci You picked ✕
Correct!
Incorrect
The answer is B: Broad QRS complex occurring early without a preceding P wave
Explanation
Why B is correct
See Ectopic Beats. Option B is correct. An ectopic beat is an extra beat that arises from a site other than the sinoatrial node, which is why it comes early, before the next normal beat is due. A ventricular ectopic starts in the ventricular muscle itself. Because it begins below the atria there is no P wave before it. The impulse cannot use the fast His-Purkinje system, so it spreads slowly from muscle cell to muscle cell across the ventricles, and the QRS complex is therefore broad and unusually shaped. The next normal beat usually follows after a pause. Ventricular ectopics are common, and patients may feel them as a missed or thumping beat. On their own, in people with a structurally normal heart, they are often harmless, but frequent ectopics, or ectopics with symptoms or heart disease, deserve further assessment. Memory aid: Ventricular ectopic: early, broad, no P wave.
- Timing: The beat comes early, before the next normal beat is due.
- P wave: Absent before the beat, because it starts below the atria.
- Shape of the QRS: Broad and unusually shaped, because the impulse spreads slowly from muscle cell to muscle cell.
Why the other options are incorrect
- A. Prolonged PR interval with otherwise normal P waves and QRS complexes: A prolonged PR interval with otherwise normal waves is first-degree atrioventricular block. It is a conduction delay and not an early beat. Your answer
- C. Inverted P wave that may be hidden within a normal QRS complex: An inverted P wave that may be hidden within a normal QRS suggests a junctional ectopic. The impulse starts near the AV node and spreads backwards into the atria. Your answer
- D. Abnormally shaped P wave appearing early followed by a normal QRS complex: An early, abnormally shaped P wave followed by a normal QRS is an atrial ectopic. The impulse starts in the atria and travels down the normal conduction system, so the QRS is narrow. Your answer
- E. Irregularly irregular rhythm caused by multiple atrial foci: An irregularly irregular rhythm from multiple atrial foci describes atrial fibrillation. A single ectopic beat is a premature beat within an otherwise regular rhythm. Your answer
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1
Which electrocardiographic pattern best characterises Mobitz type I second-degree atrioventricular block?
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2
Which electrocardiographic feature best characterises atrial fibrillation?
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