Ventricular fibrillation
Definition
The ventricular muscle fibres contract randomly causing a complete failure of ventricular function.
Epidemiology
Mostly occurs in those with pre-existing disease, particularly those with coronary heart disease. It is the most common arrhythmias in patients with a cardiac arrest. Peak incidence in 45-75 years.
Pathophysiology
Nobody's really sure exactly what happens but it usually occurs during a heart attack. Probably something to do with bad stuff happening to the heart resulting in it going out of whack and the ventricles randomly and ineffectively contracting. Or something.
Risk Factors
- CAD & MI
- VT which often precedes to VF
- Antiarrhythmic drug adminsitration
- Hypoxia
- Ischaemia
- AF
- Rapid rates in pre-excitation syndromes (e.g. WPW)
- Shock during cardioversion
- Electric shock
- Pacing to terminate VT
Clinical Features
Generally, they're having an MI so you get: chest pain, fatigue, palpitations. Commonly, a known diagnosis of pre-existing disease, particularly cardiac problems: CAD, cardiomyopathy, valvular heart disease, myocarditis, congenital heart disease and WPW.
Investigations
ECG
Most important investigation (and general thing to do) when suspecting somebody of having VF.
After the fact, look for: evidence of MI (ST elevation/depression, T wave inversion), prolonged QT interval, short PR, WPW.
Bloods
- Cardiac enzymes - troponin-T 12 hours after onset of symptoms
- U+Es - metabolic acidosis, hypokalaemia, hyperkalaemia, hypocalcaemia, hypomagnasaemia
- Drug levels of any antiarrhythmic, particularly digoxin
- Toxicology - looking for drugs like cocaine which can induce vasospasm (leads to ischaemia)
- TSH - hyperthyroidism
- CXR - signs of left heart failure, pulmonary hypertension
- Echocardiography - check for structural deficiencies
- Nuclear imaging
- Angiography