• Causes: high vagal tone (athletes), hypothyroidism, hypothermia, beta-blockers
• Usually asymptomatic; may cause dizziness, syncope if severe
• 1st degree: PR >200 ms, all P waves conducted
• 2nd degree Mobitz I (Wenckebach): progressive PR prolongation → dropped beat
• 2nd degree Mobitz II: dropped beats without PR prolongation → higher risk of CHB
• Complete heart block (CHB)
o Atria and ventricles beat independently
o Ventricular escape rhythm (regular, slow ~30–40 bpm)
o Cannon "a" waves (atria contract against closed AV valve)
• ECG: irregularly irregular, no P waves, fibrillatory baseline
• Risk factors: HTN, valvular disease (especially mitral), hyperthyroidism
• Stroke risk: CHA₂DS₂-VASc score
• Management:
o Rate control (beta-blocker, diltiazem)
o Rhythm control (if symptomatic, younger)
o Anticoagulation per stroke risk
• ECG: sawtooth flutter waves, atrial rate ~300; often 2:1 block → ~150 bpm
• Management: rate control, anticoagulation, consider ablation (curative)
• Broad complex tachycardia (>120 ms)
• Monomorphic (scar-related) vs polymorphic (torsades, ischaemia)
• Haemodynamically unstable → immediate DC cardioversion
• Antiarrhythmics: amiodarone, lidocaine
• Chaotic, no cardiac output → cardiac arrest
• Immediate defibrillation (unsynchronised DC shock)
• QTc >450 ms (men), >470 ms (women)
• Causes:
o Congenital (e.g., Romano-Ward)
o Drugs: macrolides, quinolones, antipsychotics, amiodarone, sotalol
o Electrolytes: low K⁺, Mg²⁺, Ca²⁺
• Risk of torsades de pointes → polymorphic VT
• Indications:
o Symptomatic bradycardia
o High-grade AV block (Mobitz II or CHB)
• Indications:
o Secondary prevention (survivors of VT/VF arrest)
o Primary prevention in severe LV dysfunction (EF ≤35%) with high arrhythmic risk
• Biventricular pacing for heart failure
• Indications:
o LVEF ≤35%
o QRS ≥120 ms (esp. LBBB morphology)
o Symptomatic despite medical therapy
Extra Revision Pearls
• Mobitz I clue → progressively lengthening PR, usually benign
• Mobitz II clue → sudden drop without warning → pacemaker indicated
• CHA₂DS₂-VASc ≥2 → anticoagulate (AF)
• Broad complex tachycardia = VT until proven otherwise
• Torsades clue → polymorphic VT with pause-dependent initiation
• Cannon ‘a’ waves → CHB classic sign
• AF in hyperthyroidism → always check TSH
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Author & Educational Disclaimer
Author:
Dr Phillip Cockrell BM FRCP DipClinEd
Dr Phillip Cockrell is a UK Consultant Physician in Internal Medicine, currently working at Queen Alexandra Hospital, Portsmouth University Hospitals NHS Trust. He has previously worked as a registrar across Intensive Care Medicine, Gastroenterology, Cardiology, Stroke Medicine, Acute Medicine, and Respiratory Medicine.
He has held senior leadership roles including Associate Clinical Director of the Acute Medical Unit, Clinical Director of Internal Medicine, and Chief of Medicine. Dr Cockrell has over 15 years’ experience in postgraduate medical education, having lectured extensively across the MRCP syllabus and contributed to MRCP revision teaching and course development.
Dr Cockrell holds a Bachelor of Medicine (BM), Fellowship of the Royal College of Physicians (FRCP), and a Diploma in Clinical Education (DipClinEd). His teaching approach is based on structured consolidation of complex medical topics to support efficient and effective revision for postgraduate examinations.
Purpose of this content:
The material on this page is intended solely for educational purposes to support revision for the MRCP (UK) Part 1 examination. It reflects examination-relevant principles of internal medicine and is designed to aid learning and pattern recognition.
Medical disclaimer:
This content is designed for postgraduate medical examination revision and does not constitute medical advice, diagnosis, or treatment guidance and must not be used as a substitute for professional clinical judgement, local guidelines, or specialist consultation. Clinical decisions should always be made in the context of individual patient circumstances and current national guidance.
