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Ventricular Fibrillation

Ventricular fibrillation, or VF, is the classic arrest scenario. It is a rather easy rhythm to recognize on the monitor and responds well to CPR and defibrillation, but it is deadly if not treated immediately. Essentially, the ventricles are quivering in ventricular fibrillation, thus no blood is being circulated and perfusion is nil in this rhythm. Without immediate CPR, this lethal rhythm will eventually deteriorate into asystole and death. In some situations, it may be difficult to shock a patient out of VF, and this is when drugs are used.

VF is the number one killer and is the most common rhythm seen on out-of-hospital cardiac arrest. It is the most commonly seen, the clearest to treat, and sometimes the most stubborn to reverse. This is when searching for the Hs and Ts becomes essential, because although CPR and defibrillation are important, determining the underlying cause of arrest is also very important. Another consideration is how soon CPR was started after arrest and how long the brain has gone without oxygen. If CPR isn’t started immediately, the survival rate from VF is very low.


The causes of VF are many, and they are easier to understand when they are broken down into the Hs and Ts. Possibly the most common reason for sudden cardiac arrest is a thrombosis causing an MI. This accounts for a large portion of the VF cases that occur outside of the hospital. Drugs and other toxins should also be considered. Street drugs in particular can cause abnormal heart rhythms that can lead to ventricular fibrillation. Some electrolyte imbalances, most importantly affecting potassium, can cause irritation of the myocardium and VF.

Acidosis in any form can be a prelude to an arrest. It is one of the Hs (hydrogen ions).Trauma could also potentially be a cause of ventricular fibrillation. Closely related to this is hypovolemia, which can be caused by major blood loss after a trauma. This is another well-known cause of arrest and can be reversed if it is treated early enough. Essentially, VF can occur because of any of the Hs and Ts.


Since VF involves the loss of cardiac output, patients will present as unresponsive, pulseless and apneic. If CPR is in progress, you need to stop for a pulse check. If a pulse is undetectable, continue CPR while the necessary equipment is set up. Ideally, several people will be working on the patient at the same time, so many interventions will occur simultaneously. Once the monitor is set up, you need to check the rhythm to determine which ACLS algorithm to follow.

As an ACLS practitioner, you need to be able to identify all of the different rhythms, especially the lethal ones. Ventricular fibrillation looks like random and chaotic spikes marching across the monitor. There is no organization and no regularity. Once you see a tracing of VF, it is hard to forget. When VF is present and there is no pulse, you should follow the VF algorithm for treatment.


Treatment for VF starts with early and effective CPR. Keeping the brain, heart and other vital organs perfused is very important in an arrest. Once the rhythm is identified as ventricular fibrillation, a shock should be delivered immediately. After the shock is delivered, begin CPR again for two minutes. Start thinking about what may have caused the arrest.

After two minutes of CPR, it is time to do a pulse and rhythm check. If the rhythm is anything other than VF, you should switch to the appropriate algorithm. Continued VF calls for another shock, followed by good CPR once again for 2 minutes. If the patient remains in ventricular fibrillation, administration of drugs is called for. Epinephrine is given first and may be repeated every 3 to 5 minutes. If epinephrine is not effective, the next medication that is given is amiodarone 300 mg intravenously. Defibrillation and medication are given in an alternating fashion between cycles of 2 minutes of high quality CPR. Continue until the patient achieves ROSC or the code is called.