Ventricular fibrillation: What you need to know
Ventricular fibrillation (VFib) may be confused with atrial fibrillation (AFib). Both involve irregular heart rhythms, but they affect different parts of the heart.
AFib can also signal a serious heart condition, but it is typically a symptom of a chronic problem, not a life-threatening feature in itself.
In emergency treatment, focus is on restoring blood flow as quickly as possible to the organs, including the brain. The patient may also receive treatment to minimize the risk of a recurrence.
Emergency treatments may include cardiopulmonary resuscitation (CPR) and use of a defibrillator.
Cardiopulmonary resuscitation (CPR)
Early CPR and early use of an AED can may a life.
Cardiopulmonary resuscitation (CPR) aims to restore blood flow through the body. Anybody with some basic life support training can do it.
In the past, CPR involved cycles of 30 chest compressions to the heart, and then two mouth-to-mouth resuscitation breaths.
Guidelines issued by the American Heart Association (AHA) in 2008 suggest that breathing into a person's mouth may be unnecessary.
Instead, the responder should deliver about two compressions per second, or between 100 and 120 per minute. The chest should be allowed to rise back between compressions. Once they have started, they should continue until either emergency personnel arrive or somebody comes with a portable defibrillator.
Early CPR and the use of a defibrillator increases the person's chance of survival.
Using a defibrillator
A defibrillator can be used together with CPR. The device sends electric shocks across the patient's chest. The aim is to shock the heart back into normal activity. The shock may initially stop the heartbeat, but it can also stop chaotic rhythms and restore normal function.
A public-use defibrillator can be used by a layperson. These devices often have voice instructions on their use. A public-use defibrillator is programmed to detect ventricular fibrillation and emit a shock at the right moment.
In many countries, public-use, portable defibrillators are available in public places, such as airports, major train and bus stations, shopping malls, community centers, places where elderly people gather, casinos, and so on.
When the human heart beats, electrical impulses that trigger a contraction need to follow a specific route to the heart. If there is something wrong with the path of these impulses, arrhythmia, or irregular heartbeat, may occur.
Ventricular fibrillation happens when a problem in the lower chambers cause an irregular heart rhythm.
When the muscles in the four chambers of the heart tighten, a heartbeat occurs. During a heartbeat, a chamber closes and pushes blood out.
During a heartbeat, the muscular atria, or smaller upper chambers, contract and fill the relaxed ventricles with blood.
The contraction begins when the sinus node, a small group of cells in the right atrium, emits an electrical impulse which makes the right and left atria contract.
The electrical impulse continues to the center of the heart, to the atrioventricular node. This node is located on the pathway between the atria and the ventricles. From the atrioventricular node, the impulse travels through the ventricles, making them contract.
As a result, blood is pumped out of the heart and into the body.
The most common signs of ventricular fibrillation are sudden collapse or fainting, because the muscles and brain have stopped receiving blood from the heart.
About an hour before ventricular fibrillation, some people experience:
- pain in the chest
- tachycardia, or accelerated heartbeat, and palpitations
Versus atrial fibrillation
The left and right atria form the upper chambers of the heart, and the left and right ventricles form the two lower chambers. Together, all four chambers pump blood to and from the body.
When the atria, the two upper chambers, contract at an excessively high rate, and in an irregular way, the patient has atrial fibrillation (AFib). When the two lower chambers beat irregularly and flutter, the patient has ventricular fibrillation (VFib). Both produce an irregular heart rhythm.
Ventricular fibrillation is due to defective electrical impulses. It causes the ventricles to quiver uselessly, pumping virtually no blood into the body. The heart ends up without an effective heartbeat. Blood stops flowing around the body, and vital organs, including the brain, lose their blood supply.
A patient with ventricular fibrillation will typically lose consciousness very quickly and will require immediate, emergency medical assistance, including cardiopulmonary resuscitation (CPR).
If CPR is delivered until the heart can be shocked back into a normal rhythm with a defibrillator, the patient's chances of survival are better.
VFib and AFib: Which is more serious?
Ventricular fibrillation is more serious than atrial fibrillation. Ventricular fibrillation frequently results in loss of consciousness and death, because ventricular arrhythmias are more likely to interrupt the pumping of blood, or undermine the heart's ability to supply the body with oxygen-rich blood.
VFib can cause sudden cardiac death (SCD). SCD accounts for about 300,000 deaths annually in the United States. SCD can kill a victim in minutes, and it can occur even in people who seem healthy.
The following risk factors are linked to ventricular fibrillation:
- previous ventricular fibrillation
- A previous heart attack
- cardiomyopathy, a disease of the heart muscle, or myocardium
- cocaine or methamphetamine use
- congenital heart disease, or being born with a heart defect
- electrocution or other injuries that cause heart muscle damage
Heart attack is the most common cause of ventricular fibrillation.
How is ventricular tachycardia connected to VFib?
Ventricular fibrillation usually begins with ventricular tachycardia.
Ventricular tachycardia is an abnormally rapid heart rhythm that originates from a ventricle. It happens when abnormal electrical impulses travel around a scar from a previous heart attack. It occurs in patients with some kind of heart defect.
Ventricular tachycardia can happen and then go away about 30 seconds later, without causing any symptoms. This is known as non-sustained ventricular tachycardia.
If it continues for more than about 30 seconds, it can cause palpitations, dizziness, or loss of consciousness. If left untreated, ventricular tachycardia can lead to ventricular fibrillation.
Diagnosis of ventricular fibrillation is usually happens in emergency circumstances because the patient has lost consciousness.
The following diagnostic tools can confirm ventricular fibrillation:
- A heart monitor: This device reads the electrical impulses that cause the heart to beat, and will detect either no heartbeat, or an erratic one.
- Checking the pulse: The pulse will be difficult to detect. It may either be very weak or absent.
Diagnostic tests can help to find out what caused the ventricular fibrillation.
Tools to help find the reason for VFib include an ECG.
An ECG is a medical device that monitors the electrical activity of the heart muscles.
The heart normally produces a small electric signal at every beat. An ECG will show how well the heart is functioning, whether there is any damage to the heart muscle, and whether or not the heart rhythm is normal.
Data from the ECG show whether the patient has recently had a heart attack.
Cardiac enzyme test
When a heart attack occurs, some enzymes make their way into the bloodstream. A blood test can detect these enzymes. Usually, enzyme blood levels are checked regularly over a few days.
This can assess whether the heart has any swelling, or if there is anything unusual in the heart's blood vessels.
This can detect blood flow problems to the heart. Thallium, or some other radioactive material, is injected into the bloodstream. Special cameras detect the radioactive material as it flows through the lungs and heart. This test can detect where areas of reduced blood flow to the muscles are.
This is a type of ultrasound test that utilizes high-pitched sound waves sent through a transducer, a wand-like device that is held on the chest.
The transducer picks up echoes of the sound waves as they bounce off different parts of the heart. The data appears on a video screen, where the doctor can see the heart as it moves. This test can help a doctor identify underlying structural heart disease.
Angiogram or coronary catheterization
A thin, flexible tube, or catheter, is introduced into a blood vessel until it goes through the aorta into the patient's coronary arteries.
The catheter usually enters the body at the groin or arm. A dye is injected through the catheter into the arteries. This dye stands out on images created by an X-ray and helps doctors detect coronary artery disease. Coronary artery disease happens when arteries to the heart have narrowed.
MRI or CT scan
These imaging tests can measure ejection fraction as well as the heart arteries and valves. They can also determine whether the patient had a heart attack and detect unusual causes of heart failure.
PreventionIf a physician determines that the ventricular fibrillation results from scar tissue due to a heart attack, or some structural defect in the heart, medications and medical procedures may be recommended to minimize the risk of VFib happening again. The following may be recommended:
Beta blockers are commonly used to prevent sudden cardiac arrest or ventricular fibrillation. They ease the heart's workload by making it beat more slowly and with less force. They also stabilize the heart's electrical activity. Examples include metoprolol, propranolol, timolol, and atenolol.
Angiotensin-converting enzyme (ACE) inhibitors ease the workload of the heart by opening up blood vessels and lowering blood pressure. They may also protect the heart from further damage.
A blood test will be necessary to make sure the kidneys are working properly before starting on this type of medication.
About 10 days after starting treatment, there will be further tests to make sure the kidneys are still working properly. Over a period of about 3 weeks, the dose gradually increases. Examples of ACE inhibitors include lisinopril, perindopril and ramipril.
Amiodarone (Cordarone) or calcium channel blockers may also be prescribed.
Implantable cardioverter-defibrillator (ICD)
This device is placed inside the body. It is designed to recognize certain types of arrhythmias, or abnormal heart rhythms, and correct them by emitting electric shocks to reset the heart to a normal rhythm.
In severe cases of coronary artery disease, surgery is necessary.
Angioplasty opens up the coronary artery. A small wire goes up the artery from the patient's groin or arm and is pushed until it reaches where the clot is in the coronary artery.
There is a small balloon, shaped like a sausage, at the end of the wire. The balloon is placed at the narrowest part of the artery and is then inflated, squashing the clot away. A flexible metal mesh, called a stent, is then placed there to keep that part of the artery open.
Coronary artery bypass graft (CABG)
The damaged blood vessel is by-passed with grafts taken from blood vessels elsewhere in the body. The bypass effectively goes around the blocked area of the artery, allowing blood to pass through into the heart muscle. If blood supply to the heart is improved, the risk of ventricular fibrillation goes down.
Ventricular tachycardia ablation
Catheters are inserted through a vein, usually in the groin, and threaded to the heart, to correct structural heart problems that cause an arrhythmia. The aim is to clear the signal pathway (of electrical impulses) so that the heart may beat normally again. Ablation destroys or scars tissue that blocks electrical signals.