Ventricular Fibrillation (VF)

Ventricular fibrillation (VF) is the most important shockable cardiac arrest rhythm. It is invariably fatal unless advanced life support is rapidly instituted.

ECG findings in Ventricular Fibrillation (VF)
  • Chaotic irregular deflections of varying amplitude
  • No identifiable P waves, QRS complexes, or T waves
  • Rate 150 to 500 per minute
  • Amplitude decreases with duration (coarse VF –> fine VF)
Ventricular fibrillation (rhythm strip): Chaotic irregular deflections without identifiable P-QRS-T waves

Clinical significance of VF

Ventricular fibrillation (VF) is the most important shockable cardiac arrest rhythm.

  • The ventricles suddenly attempt to contract at rates of up to 500 bpm
  • This rapid and irregular electrical activity renders the ventricles unable to contract in a synchronised manner, resulting in immediate loss of cardiac output
  • The heart is no longer an effective pump and is reduced to a quivering mess
  • Unless advanced life support is rapidly instituted, this rhythm is invariably fatal
  • Prolonged ventricular fibrillation results in decreasing waveform amplitude, from initial coarse VF to fine VF, ultimately degenerating into asystole due to progressive depletion of myocardial energy stores


In the presence of ischaemic heart disease VF may be preceded by:

The underlying mechanism of VF is not fully understood. Several mechanisms have been hypothesised:

  • Multiple wavelet mechanism: Multiple small wandering wavelets are formed, and the fibrillation is maintained by re-entry circuits formed by some of these wavelets
  • Mother rotor mechanism: A stable re-entry circuit is formed, the ‘mother rotor’. The ‘mother rotor’ then gives rise to propagating unstable ‘daughter’ wavefronts, which results in the chaotic electrical activity seen on the ECG. Animal models suggest in any instance of VF there may be one or multiple ‘mother rotors’

Causes of Ventricular Fibrillation (VF)
Toxic and Metabolic
  • Seizure
  • CVA

ECG Examples of VF
Example 1
ventricular fibrillation rhythm strip VF shock advised
  • Typical rhythm strip of VF

Example 2
ventricular fibrillation rhythm strip VF
  • Appearance of fine VF

Example 3
ECG 12 lead VF ventricular fibrillation
  • VF should never be diagnosed from the 12-lead ECG!

Example 4
ECG-Ventricular-fibrillation-VF original VF VT
  • “R on T” phenomenon causing Torsades de Pointes, which subsequently degenerates to VF
  • Notice that in this case the rhythm strip was recorded after the standard 12 leads — most ECG machines record them simultaneously

Example 5
  • R on T leads to polymorphic VT, which then degenerates to VF
  • The inferior ST elevation in the first part of the ECG may represent either inferior STEMI or simply the effects of ventricular pacing. Note the small pacing spikes in front of each QRS complex
  • The magnitude of ST elevation suggests that this is an inferior STEMI in a paced patient (see Sgarbossa’s criteria)
  • Again, the rhythm strip is recorded after the standard 12 leads.

and another example…


Example 6
ECG ventricular fibrillation VF rhythm strips
  • This patient is shocked out of VF five times in ten minutes!
  • The subsequent rhythm in each case appears to be an accelerated idioventricular rhythm (broad QRS with AV dissociation), possibly with some fusion complexes in the second and third rhythm strips


Advanced Reading



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Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner


  1. What do you mean by the statement on ECG Example 3. that “VF should never be diagnosed on a 12 lead ECG”. I think it is misleading. Please explain

    • Hi Kansiime,
      I think Drs Buttner and Burns are referring to the fact that unless you already have a 12 lead ECG on the patient and accidentally capture someone developing VF (as seen in the R on T in ECGs 4 and 5 on the page) then you are wasting precious ALS time by applying a 12 lead ECG, and you should be able to diagnose VF on a standard rhythm strip/3 lead ECG. So I would take this statement as “tongue-in-cheek”.
      I hope this answers your question / addresses your concerns!

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