What's this ECG showing?

A 45-year-old man with a history of unspecified intermittent arrhythmia presents with palpitations and dizziness.

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Source: Oliveira CC, Rocha S, Magalhães S Wide QRS arrhythmia: what is the diagnosis? Reproduced from Emergency Medicine Journal, Vol. 39, Pages 99-158, 2022 with permission from BMJ Publishing Group Ltd.