Preparatory Mindset
Arrhythmias are examined in three ways: ECG recognition (which rhythm is it?), haemodynamic triage (stable vs unstable → cardioversion if unstable), and drug/device management (which drug for which rhythm; pacemaker indications). The exam rules of thumb: (1) always treat wide-complex tachycardia as VT until proven otherwise, (2) VF/pulseless VT → immediate defibrillation + CPR + adrenaline every 3–5 min, (3) atrial fibrillation management = rate vs rhythm control + CHA₂DS₂-VASc stroke-risk scoring + anticoagulation, and (4) AV block grading decides pacing (Mobitz II and 3rd degree = pace). The HKHA arrhythmia/CPR sections are LMCHK-critical — memorise the drug doses (adenosine/ATP, amiodarone, lignocaine, digoxin) and the 5H's & 5T's.
Core Concepts
Classification
- By mechanism: disorders of impulse formation (enhanced automaticity, triggered activity) vs disorders of impulse conduction (re-entry, block).
- By rate: bradyarrhythmias (<60) vs tachyarrhythmias (>100).
- By site: supraventricular (sinus, atrial, AV junction) vs ventricular.
- Examples: sinus arrhythmia (physiological, respiratory-linked), PAC/PVC, atrial fibrillation/flutter, PSVT (AVRT — Wolff-Parkinson-White; AVNRT), VT/VF, AV block (1st/2nd/3rd degree), bundle branch blocks.
Premature contractions (PAC/PVC)
- PAC: early P wave, normal QRS — usually benign; treatment not required unless symptomatic.
- PVC: early wide QRS, no preceding P; common, increased with caffeine/stress/CHD; if frequent/complex in structural heart disease → risk of VT; NSVT in structural heart disease is an independent risk factor for cardiac mortality; treatment: correct triggers, β-blocker, antiarrhythmic in symptomatic/high-risk, consider EP study/ablation.
Atrial fibrillation (AF)
- Epidemiology: most common sustained arrhythmia; 5–10% of >65 y; paroxysms in younger patients.
- Mechanism: multiple re-entrant wavelets in atria → irregularly irregular rhythm, no P waves.
- Causes: hypertension, ischaemia, valvular (mitral), thyrotoxicosis, alcohol, obesity, OSA, post-cardiac surgery, idiopathic ("lone AF").
- Complications: thromboembolism → stroke (the major danger), heart failure, tachycardia-induced cardiomyopathy.
- CHA₂DS₂-VASc score (stroke risk): Congestive HF, Hypertension, Age ≥75 (2 points), Diabetes, prior Stroke/TIA/embolism (2 points), Vascular disease, Age 65–74, Sex category (female). Anticoagulate (DOAC/warfarin) if score ≥2 (men) / ≥3 (women); consider if 1.
- Management: acute — rate control (β-blocker, diltiazem/verapamil, digoxin) or rhythm control (amiodarone, cardioversion if unstable); anticoagulate for ≥3 weeks before and ≥4 weeks after elective cardioversion (or TEE-guided); long-term — rate vs rhythm control + CHA₂DS₂-VASc-guided anticoagulation; catheter ablation for symptomatic paroxysmal AF.
- Haemodynamically unstable AF → urgent synchronised cardioversion.
PSVT (AVNRT / AVRT-WPW)
- Regular narrow-complex tachycardia (150–250), abrupt onset/offset.
- Vagal manoeuvres first; then ATP 10–20 mg IV bolus (or adenosine 6–12 mg) or verapamil 5–15 mg IV (caution: low BP, β-blocker, reduced LVEF); synchronised cardioversion if unstable; ablation for WPW/AVRT.
Ventricular tachycardia & fibrillation
- Monomorphic VT: wide-complex regular tachycardia — treat as VT until proven otherwise; stable → amiodarone 150 mg IV over 10 min (repeat), lignocaine 1 mg/kg IV, procainamide; synchronised cardioversion (100 J).
- Polymorphic VT: unsynchronised/defibrillation (200 J); treat ischaemia, correct electrolytes (Mg²⁺), consider amiodarone/lignocaine.
- VF / pulseless VT: rapid defibrillation (360 J monophasic / 200 J biphasic or maximum) → CPR 2 min → shock → adrenaline 1 mg IV q3–5 min → amiodarone 300 mg IV (may repeat 150 mg) / lignocaine 1–1.5 mg/kg — per ALS algorithm.
AV block & bundle branch block
- 1st degree: PR >0.20 s — benign, no treatment.
- 2nd degree Mobitz I (Wenckebach): progressive PR lengthening then dropped QRS — usually benign (inferior MI, drugs).
- 2nd degree Mobitz II: fixed PR with intermittent dropped QRS (A/V ≥3:1 high grade) — risk of progression to complete block → pacemaker.
- 3rd degree (complete): atrial and ventricular independent (P waves and wide QRS dissociated) — pacemaker (emergency temporary pacing if symptomatic/bradycardic).
- RBBB/LBBB: conduction delay over the bundle branches (LBBB present in ~1% of hospital patients; ~2% of BBB develop infranodal AV block → pacemaker); new LBBB in chest pain = STEMI equivalent.
General management principles
- Haemodynamically unstable (hypotension, chest pain, heart failure, shock) → synchronised cardioversion (tachy) / pacing (brady) — drugs are second-line.
- Treat the cause: ischaemia, electrolytes (K⁺, Mg²⁺), thyroid, drugs, hypoxia, acidosis.
- Devices: pacemaker (symptomatic bradycardia, Mobitz II/3rd-degree block, bifascicular + 1st-degree, alternating BBB), ICD (VT/VF survivors, LVEF ≤35% — see heart failure chapter), ablation (PSVT, WPW, AF, VT foci).
HKHA Handbook (LMCHK) — Key Points
- VF / pulseless VT (C 4): rapid defibrillation (360 J monophasic / 200 J biphasic or max) → CPR 2 min → check rhythm → shock → adrenaline 1 mg IV q3–5 min → amiodarone 300 mg IV (consider 150 mg repeat) or lignocaine 1–1.5 mg/kg (repeat 0.5–0.75 mg/kg at 5–10 min, max 3 mg/kg).
- Asystole / PEA (C 5): BLS + ACLS, adrenaline 1 mg q3–5 min, consider reversible causes — 5H's & 5T's: Hypovolaemia, Hypoxia, Hydrogen ion (acidosis), Hyper/hypokalaemia, Hypothermia; Tension pneumothorax, Tamponade (cardiac), Toxins, Thrombosis (coronary), Thrombosis (pulmonary).
- Stable tachycardias (C 6–7): PSVT → ATP 10–20 mg IV / verapamil 5–15 mg IV (avoid if low BP, β-blocker, reduced LVEF); AF/flutter → digoxin 0.25 mg loading (0.25 mg q8h ×2), diltiazem 5–15 mg IV then 5–15 μg/kg/min, amiodarone 5 mg/kg over 60 min; wide-complex tachycardia → treat as VT (amiodarone 150 mg IV over 10 min, repeat; lignocaine 1 mg/kg then 1–4 mg/min; procainamide; synchronised cardioversion 100 J monomorphic / 200 J polymorphic).
- MI arrhythmias (C 17): symptomatic bradycardia → atropine 1 mg IV, pacing if unresponsive; Mobitz II/3rd-degree → temporary pacing (inferior MI with adequate narrow-QRS escape can be observed); additional pacing indications — bifascicular + 1st degree, RBBB + alternating LAFB/LPFB, alternating LBBB/RBBB.
- CPR (C 1–3): BLS algorithm — determine unresponsiveness, call for help + defibrillator, PPE (N95/surgical mask + gown ± gloves/goggles/face shield), high-quality chest compressions, early defibrillation.
High-Yield Points
- Wide-complex tachycardia = VT until proven otherwise (amiodarone 150 mg / lignocaine 1 mg/kg / cardioversion).
- VF/pulseless VT: defibrillate → CPR → adrenaline 1 mg q3–5 min → amiodarone 300 mg.
- PEA/asystole: adrenaline + 5H's & 5T's (treat reversible causes).
- AF: irregularly irregular, no P; CHA₂DS₂-VASc for anticoagulation; rate vs rhythm control.
- AV block: Mobitz II & 3rd degree → pacemaker; Wenckebach benign.
- PSVT: vagal → ATP 10–20 mg / verapamil; unstable → cardioversion.
- LBBB present ~1% hospitalised; new LBBB + chest pain = STEMI equivalent.
- NSVT in structural heart disease = independent mortality risk.
Topic Summary
Arrhythmias are approached by ECG recognition, haemodynamic stability, and mechanism. Supraventricular rhythms (AF, PSVT) are managed with rate/rhythm control (β-blocker, calcium blockers, digoxin, amiodarone) and stroke-risk-guided anticoagulation (CHA₂DS₂-VASc); ventricular rhythms demand urgency — defibrillation for VF/pulseless VT with adrenaline and amiodarone, and "treat as VT" for wide-complex tachycardia. Bradyarrhythmias follow the AV-block ladder (1st degree and Wenckebach conservative; Mobitz II and 3rd degree paced). The HKHA CPR/arrhythmia protocol — including the 5H's & 5T's for PEA/asystole and the MI-complication drug doses — is an LMCHK priority.