What Is Ventricular Fibrillation? What Causes Ventricular Fibrillation?
Ventricular fibrillation is an abnormally irregular heart rhythm caused by rapid, uncoordinated fluttering contractions of the ventricles - the lower chambers of the heart. These fluttering replace normal contractions. Ventricular fibrillation puts the heartbeat and pulse beat out of synch.
The pumping chambers in the ventricles quiver uselessly, instead of pumping blood, resulting in a serious drop in blood pressure, and the cutting off of oxygen-rich blood to body organs.
Ventricular fibrillation is a life-threatening medical emergency. It is most commonly linked to heart attacks or scarring of the heart muscle from previous heart attack. A patient with ventricular fibrillation generally collapses within seconds - and it won't be long before his/her breathing or pulse stops.
What is the difference between ventricular fibrillation and atrial fibrillation?The human heart has two upper chambers and two lower chambers. The upper chambers are called the left atrium and the right atrium - the plural of atrium is atria. The two lower chambers are the left ventricle and the right ventricle. When the two upper chambers - the atria - contract at an excessively high rate, and in an irregular way, the patient has atrial fibrillation. When the two lower chambers beat irregularly and flutter, the patient has ventricular fibrillation.
Put simply - atrial fibrillation refers to the two upper heart chambers while ventricular fibrillation refers to the two lower heart chambers; in either case there abnormally irregular rhythm.
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.
Sudden cardiac death (SCD) accounts for about 300,000 deaths annually in the USA, of which 75% to 80% are due to ventricular fibrillation, according to the NIH (National Institutes of Health). The NIH adds that more deaths are attributable to ventricular fibrillation than to breast, cancer, AIDS or lung cancer.
Ventricular fibrillation is typically the first expression of coronary artery disease (CAD) and is responsible for approximately 50% of deaths from CAD.
According to Medilexicon's medical dictionary:
Ventricular fibrillation is "coarse or fine, rapid, fibrillary movements of the ventricular muscle that replace the normal contraction."
What are the signs and symptoms of ventricular fibrillation?A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.
The most common sign of ventricular fibrillation is:
- Sudden collapse, loss of consciousness or fainting; because the brain and muscles have stopped receiving blood from the heart.
- Pain in the chest
- Tachycardia - accelerated heartbeat, palpitations
What are the risk factors for ventricular fibrillation?A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2.
The following risk factors are linked to ventricular fibrillation:
- Having had ventricular fibrillation before
- A previous heart attack
- Cardiomyopathy - disease of the heart muscle (myocardium)
- Cocaine and/or methamphetamine use
- Congenital heart disease - being born with a heart defect
- Electrocution or other injuries that resulted in heart muscle damage
What are the causes of ventricular fibrillation?When the human heart beats, electrical impulses that trigger a contraction need to follow a specific route (pathway) to the heart. If there is something wrong with the path of these impulses, i.e. if there is an interruption to these impulses, arrhythmia (irregular heartbeat) may occur.
The heart is divided into four hollow chambers - the upper chambers are called the atria (singular: atrium) and the lower chambers are called the ventricles. The walls of the atria and ventricles are made virtually of 100% pure muscle. A heartbeat is caused by the tightening of these muscles. When the muscles tighten the chambers squeeze closed and push out the blood which is inside them.
During a heartbeat the muscular atria (the smaller chambers) contract and fill the relaxed ventricles with blood. The contraction begins when the sinus node (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, resulting in blood being pumped out of the heart and into the body.
How does ventricular fibrillation start? In the majority of cases ventricular tachycardia occurs. Ventricular tachycardia is an abnormally rapid heart rhythm that originates from a ventricle. It is caused by abnormal electrical impulses that travel around a scar which developed from a previous heart attack. Ventricular tachycardia occurs in patients with some kind of heart defect.
Ventricular tachycardia can occur and then go away about 30 seconds later and cause no symptoms - this is known as non-sustained ventricular tachycardia. If it continues for more than about 30 seconds it will generally cause palpitations, dizziness and/or loss of consciousness. If left untreated, ventricular tachycardia can lead to ventricular fibrillation.
Ventricular fibrillation is when the ventricles quiver uselessly, pumping virtually no blood into the body - this is caused by disordered electrical impulses. The heart ends up without an effective heartbeat; blood stops flowing around the body and vital organs, including the brain lose their much needed blood supply.
A patient with ventricular fibrillation will typically lose consciousness very quickly and will require immediate, emergency medical assistance, including CPR (cardiopulmonary resuscitation). If CPR is delivered until the heart can be shocked back into a normal rhythm with a defibrillator, the patient's chance of survival are much better.
Diagnosing ventricular fibrillationDiagnosis of ventricular fibrillation is usually done in emergency circumstances, because most likely the patient has lost consciousness. The following diagnostic checks can confirm ventricular fibrillation:
- A heart monitor - this device reads the electrical impulses that cause the heart to beat and will detect either no heart beat or an erratic one.
- Checking the pulse - the pulse will be difficult to detect, it may either be very weak or not there at all.
- ECG (electrocardiogram) - a medical device that monitors the electrical activity of the heart muscles. Our hearts produce a small electric signal at every beat. A heart specialist (cardiologist) can use this device to see how well the heart is functioning, whether there is any damage to the heart muscle, or abnormalities with the heart rhythm. A doctor can tell, when checking the data coming from the ECG, whether the patient has had a heart attack recently, or even earlier. Heart attack is a common cause of ventricular fibrillation.
- Cardiac enzyme test - when a person has a heart attack 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.
- Chest X-ray - this can be useful to see if the heart has any swelling, or if there is anything unusual with the heart's blood vessels.
- Nuclear scan - can detect blood flow problems to the heart. Thallium, or some other radioactive material is injected into the bloodstream. The radioactive material is detected by special cameras as it flows through the lungs and heart. This test can detect where areas of reduced blood flow to the muscles are.
- Echocardiogram - This is a type of ultrasound test that utilizes high-pitched sound waves that are 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 patient's heart. The data is presented 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 (coronary catheterization) - a catheter (thin, flexible tube) 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 (arteries to the heart that have narrowed).
- Cardiac MRI (magnetic resonance imaging) or CT (computed tomography) scan - they can measure ejection fraction as well as the heart arteries and valves. They can also determine whether the patient had a heart attack. These scans are also useful in seeking out unusual heart failure causes.
What are the treatment options for ventricular fibrillation?In emergency treatment, focus is on restoring blood flow to organs throughout the body, including the brain - in other words, restoring blood flow as soon as possible. When this is done, the patient may receive treatment to prevent or minimize a recurrence.
Emergency treatments may, and will probably include:
- CPR (cardiopulmonary resuscitation) - can restore blood flow through the body. CPR can be done by anybody with some basic life support training.
Manual chest compressions and mouth-to-mouth
- 30 chest compressions to the heart and then
- Two mouth-to-mouth resuscitation breaths (mouth-to-mouth)
Most health care professionals these days say that breathing into the person's mouth is not necessary. The patient should receive about two compressions per second, or between 100 and 120 per minute - the chest should be allowed to rise back between compressions. This should be continued until either emergency personnel arrive or somebody comes with a portable defibrillator.
- Defibrillator - This is a CPS medical device. It sends electric shocks across the patient's chest - the aim is to use electricity to shock the heart back into proper activity. Initially, the electric shock stops the heart momentarily - but it also stops the chaotic heart rhythm, which usually restores normal heart rhythm.
A public-use defibrillator can be used by a lay person. 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 most countries, especially industrialized nations, public-use (portable) defibrillators will be available in public places, such as airports, major train and bus stations, shopping malls, community centers, places where elderly people gather, casinos, etc.
If a physician determines that the ventricular was cause by scarred tissue from a heart attack, or some structural defect in the heart, medications and medical procedures may be recommended to minimize the risk of recurrence. The following may be recommended:
- Beta blockers are commonly used to prevent sudden cardiac arrest or ventricular fibrillation. These drugs make the heart beat more slowly and with less force, thus easing the heart's workload. They also stabilize the heart's electrical activity. Examples include metoprolol, propranolol, timolol, and atenolol.
- ACE (angiotensin-converting enzyme) inhibitors - these drugs help ease the workload on the heart by opening up blood vessels and lowering blood pressure. Experts say ACE inhibitors also protect the heart from further damage. Patient will have a blood test to make sure their kidneys are working properly before starting on this type of medication. Then, about ten days after starting treatment, the patient will undergo further tests to make sure his/her kidneys are still working fine. Over a period of about 3 weeks the patient's dose is gradually increased. Examples of ACE inhibitors include lisinopril, perindopril and ramipril.
- Amiodarone (Cordarone) or calcium channel blockers may also be prescribed.
- ICD (implantable cardioverter-defibrillator) - this device is placed inside the body. It is designed to recognize certain types of arrhythmias (abnormal heart rhythms) and correct them by emitting electric shocks to reset the heart to a normal rhythm.
- Coronary angioplasty - this surgical procedure is sometimes necessary in severe cases of coronary artery disease. 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.
- CABG (Coronary artery bypass graft) - 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. Put simply, tissue that blocks the electrical signal is either destroyed or scarred.