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Fundamentals of ECG · MBBS / Medicine · 23 practice questions
- Causes of axis deviation - distinguishing right vs left
- T wave inversion - causes and normal variants
- Bundle branch block ECG criteria
- Wide QRS complexes - differential diagnosis
- ST segment depression - digoxin vs ischaemia
- Rhythm analysis - variable PR interval
- QRS complex evaluation and hypertrophy patterns
- ST segment changes
1. A patient with chronic diuretic use for hypertension has an ECG showing flattened, prolonged T waves and prominent U waves. Serum potassium is most likely to show which abnormality?
- AHypokalaemia
- BHypercalcaemia
- CHyperkalaemia with digoxin toxicity
- DHyperkalaemia
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A. Hypokalaemia Flat, prolonged T waves together with U waves are described as features of hypokalaemia, which is a recognized complication of chronic diuretic therapy. Hyperkalaemia instead produces peaked, tall T waves, the opposite pattern. Hypercalcaemia is not discussed in relation to T or U wave changes in this material. Hyperkalaemia with digoxin toxicity is not supported since digoxin causes ST depression and the potassium change described is peaked T waves, not flattened ones.
2. On a rhythm strip, the PR interval progressively lengthens over three consecutive beats until one P wave fails to conduct, after which the pattern of gradual PR prolongation resumes. Which conduction abnormality does this represent?
- AFirst degree block
- BMobitz type 2 second degree block
- C2:1 second degree block
- DWenckebach (Mobitz type 1) second degree block
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D. Wenckebach (Mobitz type 1) second degree block Progressive PR lengthening followed by a nonconducted P wave, then repetition of the cycle, defines Wenckebach (Mobitz type 1) block. Mobitz type 2 instead shows occasional nonconducted beats without preceding progressive PR lengthening. First degree block has a fixed PR interval over 200 ms with one P wave per QRS and no dropped beats. 2:1 block shows two P waves for every QRS with a constant, normal P wave rate, not progressive PR prolongation.
3. A 45-year-old woman with sudden-onset dyspnoea has an ECG showing a Q wave in lead III that is absent in lead VF, along with right axis deviation. There is no Q wave in any other lead. Which of the following is the most likely explanation for this finding?
- AInferior myocardial infarction
- BNormal variant unrelated to any pathology
- CPulmonary embolism
- DSeptal hypertrophy
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C. Pulmonary embolism A Q wave in lead III but not VF combined with right axis deviation is suggestive of pulmonary embolism, fitting this patient's acute dyspnoea. An isolated Q wave in lead III without VF involvement alone (without right axis deviation) would be a normal variant, but the additional right axis deviation changes the significance here. Inferior myocardial infarction would be expected to show Q waves in more than one lead (e.g., both III and VF), which is not the case. Septal hypertrophy is not a described cause of this specific Q wave pattern in the source.
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