PassFinals
Cardiovascular

Ventricular Fibrillation (VF)

Ventricular fibrillation is chaotic, disorganised ventricular electrical activity that produces no coordinated contraction, so the circulation stops and the patient is in cardiac arrest.

In a nutshell

Ventricular fibrillation (VF) is a shockable cardiac arrest rhythm: chaotic ventricular activity, no output, no pulse. Start cardiopulmonary resuscitation (CPR), attach a defibrillator and give one unsynchronised shock of at least 150 J on a standard biphasic device, then resume compressions for 2 minutes.

Classic presentation

An adult collapses suddenly, unresponsive with agonal gasps and no pulse; the defibrillator shows a chaotic waveform with no organised QRS complexes (normal ventricular beats).

Key points

  • Coronary heart disease causes about 80% of sudden cardiac death; non-ischaemic cardiomyopathy 10% to 15%. Inherited disease, congenital defects, myocarditis and substance misuse dominate in the young.
  • Fine VF is still VF: shock it. Amplitude does not predict shock success, and there is no role for waveform analysis to time the shock.
  • A defibrillator that filters compression artefact may let you read the rhythm without pausing. If it shows asystole, do not stop compressions for a rhythm check.
  • CPR-induced consciousness happens. Small doses of a sedative or analgesic are reasonable; a neuromuscular blocker alone in a conscious patient is not.
  • Obese patients get standard basic and advanced life support at standard energies. Nothing about the algorithm changes.
  • 45 minutes of advanced life support (ALS) in persistent asystole, with no reversible cause found, is the usual point at which a team considers stopping.
  • Unexplained VF needs toxicology and genetic samples, device and wearable downloads, repeat ECGs, cardiac MRI, sodium-channel-blocker testing and exercise testing, with long-term follow-up.

First-line investigation

Rhythm assessment on the attached defibrillator during a pause of under 5 seconds; no 12-lead ECG, blood test or ultrasound scan comes first.

Management

Recognise, compress, shock

  • Unresponsive with absent or abnormal breathing: call 2222 in hospital or 999 outside, start CPR 30:2, attach pads. VF and pulseless ventricular tachycardia (VT) are shockable; pulseless electrical activity and asystole are not.3,1,2
  • Compress at 100 to 120 per minute, at least 5 cm but no more than 6 cm deep, with full recoil and no leaning. Charge during compressions.3,1
  • Oxygen mask or bag-valve mask at least 1 m from the chest, pads more than 8 cm from any pacemaker or implantable cardioverter defibrillator (ICD), never shock during compressions.1
  • Antero-lateral pads, lateral pad directly below the armpit in the mid-axillary line. Shock VF of any amplitude. Keep the pause around the shock under 5 seconds.1
  • At least 150 J for rectilinear or truncated exponential biphasic, 130 to 150 J for pulsed biphasic, highest adult setting if the device recommendation is unknown.1
  • Resume compressions for 2 minutes straight after every shock, with no routine pulse check. Escalate energy on later shocks if the device allows.1,2

Drugs, airway, monitoring and reversible causes

  • IV access first, intraosseous (IO) if two IV attempts fail. After three shocks: adrenaline 1 mg IV or IO, then 1 mg every 3 to 5 minutes.1,2
  • Amiodarone 300 mg IV after three shocks, 150 mg IV after five, whether the shockable rhythm is continuous or intermittent. Never delay a shock for a drug.1
  • Where amiodarone is unavailable, or the local decision is to use lidocaine: lidocaine 100 mg IV, then 50 mg after five defibrillation attempts.1
  • Once a tracheal tube or supraglottic airway is in, ventilate 10 per minute with continuous compressions. Give the highest feasible inspired oxygen throughout.1
  • Waveform capnography confirms tube position, tracks compression quality and flags return of spontaneous circulation (ROSC). With an arterial line, aim diastolic above 30 mmHg, end-tidal carbon dioxide above 3.3 kPa.1
  • 4Hs: hypoxia, hypovolaemia, metabolic (potassium, calcium, magnesium, glucose), hypo- or hyperthermia. 4Ts: thrombosis (coronary or pulmonary), tension pneumothorax, toxins, tamponade.1,2
  • Do not routinely give calcium, sodium bicarbonate or corticosteroids. Give fluid only if hypovolaemia caused the arrest.1

Refractory VF

  • Refractory VF is continuous VF after three consecutive shocks. Recheck pad adhesion and position, shave hairy sites, escalate the energy.1
  • After a failed third shock, prepare fresh pads for an antero-posterior change at the next rhythm check: anterior left of the sternum, posterior medial to the left scapula.1
  • Routine dual sequential defibrillation is not recommended. Call senior and critical care help early; extracorporeal CPR only within a service set up to deliver it.1

When the algorithm changes

  • Hyperkalaemic arrest: calcium chloride 10% 10 mL IV and sodium bicarbonate 50 mmol IV, through separate lines or with a flush between them.4
  • Hypothermic arrest: if VF persists after three shocks, hold further shocks until the core temperature is above 30°C.4
  • Below 30°C adrenaline is held altogether. At a core temperature of 30 to 35°C, give 1 mg IV every 6 to 10 minutes.4
  • One amiodarone 300 mg loading dose if the rhythm is shockable in hypothermia, but no further doses until the core temperature is above 30°C.4
  • Suspected pulmonary embolism: give a fibrinolytic drug, then continue CPR for 60 to 90 minutes before considering stopping.4,1
  • Ceiling of care: check for a DNACPR (do not attempt cardiopulmonary resuscitation) recommendation or a ReSPECT (Recommended Summary Plan for Emergency Care and Treatment) plan.7
  • A plan guides, it does not bind. Unless a legally binding document is in place, the professionals at the bedside make the final call.7
  • Stopping is a team decision on duration, reversible causes and response to treatment. Termination-of-resuscitation rules are not for in-hospital arrest. Debrief immediately afterwards.7,1

After ROSC

  • ABCDE (airway, breathing, circulation, disability, exposure), intubate if still comatose. Target oxygen saturation 94% to 98% or arterial oxygen 10 to 13 kPa, carbon dioxide 4.7 to 6.0 kPa.5,2
  • Mean arterial pressure above 60 to 65 mmHg, or systolic above 100 mmHg. Get a 12-lead ECG and early echocardiography.5
  • Immediate coronary angiography within 120 minutes for clear ST elevation, the ECG pattern of coronary occlusion. Consider it too for haemodynamic or electrical instability.4,5
  • If still comatose, actively prevent fever at 37.5°C or below for 36 to 72 hours. This is fever prevention, not the old 32 to 36°C cooling window.5
  • Do not actively rewarm a comatose patient sitting at 32 to 36°C. That is a separate rule, and not a temperature to aim for.5
  • An arrhythmia immediately after ROSC is itself a life-threatening feature: treat it on the peri-arrest pathway and correct the cause. No prophylaxis if none persists.5,1

Disposition, prevention and driving

  • Admit to critical care or a cardiac arrest centre with continuous rhythm and blood pressure monitoring and early cardiology involvement.5
  • NICE technology appraisal TA314 recommendation 1.1: an ICD for a survivor of VF- or VT-caused cardiac arrest with no treatable cause.6
  • Assess physical and non-physical impairment before discharge, refer for early rehabilitation, and arrange cardiac arrest follow-up within three months.5
  • Driving: a ventricular arrhythmia leading to an ICD indication or recommendation means 6 months off Group 1 (car and motorcycle) driving, with Driver and Vehicle Licensing Agency (DVLA) notification.8
  • A Group 2 (lorry and bus) licence is revoked permanently. A prophylactic ICD is a separate row: one month off Group 1 driving.8

Exam traps

  • A pulseless VT trace is treated exactly like VF. A VT trace with a pulse goes down the peri-arrest tachyarrhythmia pathway instead.
  • Cardiac arrest shocks are unsynchronised. Synchronised cardioversion is for a tachyarrhythmia with a pulse and is the wrong button here.
  • Adrenaline is not the first drug in a shockable arrest: it waits for three shocks. In a non-shockable arrest it is given at once.
  • Do not stop to read the monitor after a shock. Restart compressions immediately and reassess at the end of the 2 minutes.
  • Calcium and bicarbonate are not routine arrest drugs, but withholding them in a hyperkalaemic arrest is the error, not the rule.
  • Post-arrest temperature control is fever prevention at 37.5°C or below, not the old 32 to 36°C targeted temperature management window.
  • A short burst of seizure-like activity at collapse is usually the arrest itself, not a fit. Once it stops, assess breathing.
  • An arrhythmia immediately after ROSC counts as a life-threatening feature in its own right, even without shock, syncope, ischaemia or heart failure.
  • An ICD is for an arrest with no treatable cause. Successful revascularisation does not automatically remove the indication without electrophysiology review.
  • A defibrillator cannot fix a cold heart. Below 30°C, further shocks after the first three and adrenaline both wait for rewarming.

Illustrations

Ventricular fibrillation on a 12-lead tracingChaotic ventricular activity of varying amplitude with no consistent organised QRS complexes. In clinical practice, VF is identified on the attached defibrillator during cardiac arrest; a diagnostic 12-lead ECG must never delay the first shock.Jer5150, Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. Adult advanced life support Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  2. Adult advanced life support algorithm 2025 (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  3. Adult basic life support Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  4. Special circumstances Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  5. Post-resuscitation care Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  6. Implantable cardioverter defibrillators and cardiac resynchronisation therapy for arrhythmias and heart failure (NICE TA314, recommendation 1.1)Published 25 Jun 2014 | Updated 30 Aug 2017
  7. Ethics Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  8. Assessing fitness to drive: cardiovascular disorders (DVLA medical guidance)Published 11 Mar 2016 | Updated 7 Nov 2025

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.