Key Facts

Ventricular fibrillation (VF) is a chaotic cardiac rhythm originating from multiple re-entrant circuits within the ventricles, resulting in no coordinated ventricular contraction and therefore no cardiac output. It is invariably fatal without immediate defibrillation.

Epidemiology

• ~60,000 out-of-hospital cardiac arrests (OHCA) per year in the UK
• VF/pulseless VT is the initial rhythm in ~25% of OHCA (declining proportion)
• Overall OHCA survival to discharge: ~8-10%
• VF/pVT has the best prognosis of all arrest rhythms if defibrillated promptly
• Bystander CPR doubles survival; immediate defibrillation can achieve >50% survival

Aetiology

• Acute myocardial ischaemia/infarction: most common cause
• VT degeneration: sustained VT → VF
• Reversible causes (4Hs and 4Ts): hypoxia, hypovolaemia, hypo/hyperkalaemia, hypothermia, thrombosis (coronary/PE), tension pneumothorax, tamponade, toxins
• Inherited conditions: long QT syndrome, Brugada, CPVT, HCM, ARVC
• Electrolyte abnormalities: hypokalaemia, hypomagnesaemia
• Drug toxicity: proarrhythmic drugs, cocaine, digoxin

Pathophysiology

• Multiple re-entrant wavelets propagating chaotically through ventricular myocardium
• No organised depolarisation → no coordinated contraction → no cardiac output
• Brain damage begins within 3-5 minutes without perfusion
• Degenerates from coarse VF → fine VF → asystole over time without treatment
• Defibrillation simultaneously depolarises the entire myocardium, allowing the sinus node to resume control

Presentation

• Sudden loss of consciousness
• No pulse (cardiac arrest)
• No breathing or agonal gasps only
• Rapidly progresses to death without intervention

Preceding Symptoms (if witnessed)

• Chest pain (ischaemia)
• Palpitations
• Dizziness or syncope
• Dyspnoea
• May occur without any warning

Settings

• Out-of-hospital: home, public places (community AEDs)
• In-hospital: coronary care, cath lab, emergency department
• Exercise-related: suspect HCM, ARVC, LQTS, anomalous coronary artery
• Post-MI: highest risk in first 48 hours

Red Flags

• Any cardiac arrest is a red flag requiring immediate action
• Family history of sudden cardiac death in young (<40 years)
• Prior syncopal episodes with exertion
• Known structural heart disease or channelopathy

Bedside (during resuscitation)

• Cardiac monitor/defibrillator: rhythm analysis — confirms VF
• ABG: pH, K⁺, lactate, oxygenation
• Point-of-care USS: cardiac activity, tamponade, PE, LV function
• Capnography: ETCO₂ monitoring during CPR (confirms ETT placement, guides CPR quality, ROSC detection)

Bloods (post-ROSC)

• Troponin: MI assessment
• U&Es: K⁺, Mg²⁺ — correct abnormalities
• FBC, glucose, lactate: metabolic status
• Coagulation: DIC screen
• Toxicology: if drug-related arrest suspected

Imaging (post-ROSC)

• Coronary angiography: urgent if STEMI or suspected ACS
• CT head: if neurological deficit
• CTPA: if PE suspected
• Echocardiography: LV function, structural abnormalities

Special Tests (post-ROSC)

• Cardiac MRI: scar assessment, viability
• EP study: inducibility testing
• Genetic testing: if suspected channelopathy or familial condition

Non-pharmacological

Immediate (ALS algorithm):

1. Confirm cardiac arrest: unresponsive, no normal breathing
2. Call for help, start CPR 30:2 (100-120 compressions/min, 5-6cm depth)
3. Attach defibrillator → rhythm analysis
4. VF confirmed: deliver unsynchronised shock (150-200J biphasic)
5. Resume CPR immediately for 2 minutes (do not pause to check rhythm)
6. Rhythm check at 2 minutes → shock if still VF
7. Continue cycle: CPR 2 min → shock → CPR 2 min → shock

Pharmacological (during ALS)

• After 3rd shock: amiodarone 300mg IV bolus (diluted in 5% dextrose)
• After 5th shock: amiodarone 150mg IV bolus
• Adrenaline 1mg IV every 3-5 minutes (after 3rd shock in VF/pVT; immediately in non-shockable rhythms)
• Address reversible causes: 4Hs and 4Ts
• Correct K⁺ >4.0 mmol/L, Mg²⁺ >1.0 mmol/L

Post-ROSC (return of spontaneous circulation):

• Targeted temperature management: 32-36°C for ≥24 hours (TTM2 trial: 33°C vs 36°C — no difference)
• Coronary angiography: if STEMI or suspected ACS — emergent PCI
• ICU management: ventilation, haemodynamic support, seizure management
• Neuroprognostication: at ≥72 hours post-ROSC (multimodal approach)

Surgical/Interventional

• Emergency PCI: if acute coronary occlusion
• ICD implantation: secondary prevention if survived VF arrest with treatable cause excluded
  • Wait ≥40 days post-MI; ≥3 months after revascularisation
• VT ablation: if recurrent VT/VF with identifiable substrate
• Wearable cardioverter-defibrillator (LifeVest): bridge to ICD decision

Referral Criteria

• All cardiac arrest survivors: ICU, cardiology review
• Consider referral to specialist inherited cardiac conditions service if young, structurally normal heart
• Family screening if inherited condition suspected

• Overall OHCA survival to discharge: ~8-10%
• VF/pVT arrest: best prognosis of all arrest rhythms (~25-30% survival if promptly defibrillated)
• Every minute delay in defibrillation reduces survival by 7-10%
• Bystander CPR doubles survival
• Neurological outcome: ~50% of survivors have good neurological recovery (CPC 1-2)
• In-hospital VF arrest: survival ~40-50%
• Post-MI VF (within 48h): does not independently worsen long-term prognosis if revascularised
• Late VF (>48h post-MI or with structural disease): ICD indicated, high recurrence risk without

ALS Shockable Rhythm Algorithm Summary

Reversible Causes (4Hs and 4Ts)