Ventricular fibrillation

The diagnosis of ventricular fibrillation (VF) refers to a cardiac arrhythmia in which disorganized electrical activity within the heart causes uncoordinated contraction of the ventricular myocardium. The heart is subsequently unable to pump blood normally to the body, leading to cardiac arrest. VF is one of the shockable cardiac arrest rhythms, the other being ventricular tachycardia.

Clinical presentation

Ventricular fibrillation is one of four possible states that may be found in an unconscious patient who has undergone a cardiac arrest. In a state of ventricular fibrillation, irregular depolarization of the ventricular myocardium leads to disordered, high frequency ventricular contractions. As the ventricles lose their ability to contract synchronously, there is failure of ventricular function and therefore loss of cardiac output. The electrocardiogram demonstrates a chaotic, irregular waveform with deflections of varying morphology and amplitude. There are no discernible P waves, QRS complexes or T waves. Ventricular fibrillation is often associated with underlying structural heart disease.

Pathology

Etiology

The underlying causes have been classically described as the four Hs and Ts :

• hypoxia
• hypovolemia
• hyperkalemia/hypokalemia/hypoglycemia/other metabolic disorders
• hypothermia
   
• thrombosis
  • cardiac (acute coronary syndrome) or pulmonary embolism
• tamponade (cardiac)
• toxins
• tension pneumothorax

Ventricular fibrillation is commonly associated with underlying structural heart disease.

Treatment and prognosis

The prognosis of ventricular fibrillation depends on the time between onset and medical intervention. Defibrillation is the most effective intervention for patients in cardiac arrest secondary to VF, and early defibrillation can strongly improve chances of survival .