Ventricular fibrillation

Question 1

Define ventricular fibrillation.

Answer 1

A life-threatening cardiac arrhythmia in which the coordinated contraction of the ventricular myocardium is replaced by high-frequency, disorganized excitation → no uniform ventricular activation or contraction, no cardiac output, and no recordable blood pressure

Question 2

How common is VF?

Answer 2

VF is the most commonly identified arrhythmia in cardiac arrest patients.

VF incidence parallels with incidence of IHD with peak occurring in 45-75yr olds.

Question 3

What are the risk factors for VF?

Answer 3

CAD - most common factor predisposing to VF

Rapid VT can lead to VF

Other:

• Antiarrhythmic drug administration
• Hypoxia
• Ischaemia
• AF
• Rapid ventricular rates in pre-excitation syndrome
• Electrical shock administered during cardioversion
• Electrical shock caused by improperly grounded equipment
• Competitive ventricular pacing to terminate VT
• Smoking
• Male
• Hypotension
• Hypokalaemia

Question 4

How does VF present?

Answer 4

• Syncope +/- cardiac arrest - no CO, no recordable BP
• Followed by asystole
• Hx of heart disease

Question 5

What investigations would you do for VF?

Answer 5

ECG - no uniform ventricular activation, evidence of MI, prolonged QT, short PR, WPW pattern or other.

Cardiac enzymes - CK, myoglobin, troponin

Electrolytes - hyperkalaemia, hypokalaemia, hypocalcaemia, hypomagnesaemia, metabolic acidosis can predispose to arrhythmia and sudden death.

Drug levels - TCAs, digoxin, anti-arrhythmic medications

Toxicology screen - cocaine can cause vasospasm induced ischaemia

TSH - hyperthyroidism can cause tachycardia/tachyarrhythmias

CXR - signs of LH failure, pulmonary hypertension

Echo - structural abnormalities or cardiac dysfunction

Coronary angiography - assess ventricular function if the patient survives , may identify patients suitable for PCI or CABG

Question 6

How do you manage VF?

Answer 6

Advanced life support guidelines:

• Follow DRSABC then start compressions
• Deliver shock as soon as defibrillator available with 120-150J
• Continue CPR for 2mins
• Shock again
• Continue CPR for 2 mins
• Shock again
• Give adrenaline 1mg IV/IO after 3rd shock then every 3-5mins
• Give amiodarone 300mg IV/IO for after 3 shocks then consider a dose of 150mg IV/IO after the 5th shock

Magnesium (in those with cardiac arrest due to torsades de pointes)

Stabilisation:

Full assessement of ventricular function should be done and treatment of underlying cause if possible.

Question 7

What are the complications of VF?

Answer 7

• CNS ischaemic injury
• Myocardial injury
• Post-defib arrhythmias
• Aspiration pneumonia
• Injuries from CPR
• Skin burns
• Death

Question 8

What is the prognosis with VF?

Answer 8

Depends on time between onset and medical intervention (poor if intervention >4-6mins after onset)

VF that occurs more than 48 hours after acute MI is associated with a high rate of recurrence and a poorer prognosis.

Prognosis largely depends on haemodynamic stability, early neurological recovery and duration of resuscitation.

Question 9

What changes on ECG indicated a poor prognosis in VF?

Answer 9

Manifests as chaotically irregular pattern. Initially coase but becomes finer as ventricular disorganisation increases. As ECG waveform flattens, likelihood of successful defibrillation decreases.

Question 10

What is the other shockable rhythm?

Answer 10

VT

Non shockable: PEA and asystole

Question 11

What is the long term management of someone who has had VF?

Answer 11

Implantable cardioverter defibrillators (ICDs)

+/- CABG - if the cause was ischaemia