You are a Hong Kong medical examiner. Generate 50 high-yield MCQs on Arrhythmias and blocks for HK-MLE preparation. Use clinical vignettes with ECG descriptions (no images — describe the tracing). Cover ALL subtopics: AF (CHA2DS2-VASc, rate vs rhythm, anticoagulation), SVT/AVNRT/WPW, VT/Torsades, Bradyarrhythmias (sick sinus), AV blocks (1st, Mobitz I/II, 3rd degree), BBB, antiarrhythmics (Vaughan-Williams). For each question provide: 1. Correct answer 2. One-sentence explanation why correct 3. One-sentence explanation for each distractor Weight toward: AF (25%), VT vs SVT (25%), AV blocks (25%), antiarrhythmics (25%). Include HKMLE trap answers (e.g., adenosine in WPW+AF, atropine in Mobitz II). Base on Davidson's + 2024-2025 ESC guidelines. Format: Q#. Vignette + A-E. Answer: X — explanation. Distractors: A) explanation B) explanation C) explanation D) explanation E) explanation. End with subtopic summary table.