The patient was a 22-year-old man with a 8-year history of episodes of a rapid heart rhythm. A 12-lead ECG during sinus rhythm (not shown) was normal. The ECG of Fig. 1 was recorded in the catheterisation room after adenosine administration and shows sinus rate slowing, changes in QRS configuration and an episode of complete AV block. Thereafter AV conduction resumes.
Can you explain the QRS changes in beats 3 to 6, and those in beats 7 to 11?
You will find the answer elsewhere in this issue.
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