ECG of the Week - 12th October 2015

The following ECG's are from a 17 yr old male who presented with palpitations for the last hour. He is normal fit and well. He denies taking any medications or drugs.
I don't know the exact time frames between these ECG's and what treatment, if any, was instituted between them.

ECG 1
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ECG 2
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ECG 3
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ECG 4
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ECG 5
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Things to think about

• What are the key features on each ECG ?