What is it?
- Ventricular fibrillation occurs when the heart beats with rapid, erratic electrical impulses. This causes pumping chambers in your heart (the ventricles) to quiver uselessly, instead of pumping blood. During ventricular fibrillation, your blood pressure plummets, cutting off blood supply to your vital organs.
- Ventricular fibrillation is an emergency that requires immediate medical attention. A person with ventricular fibrillation will collapse within seconds and soon won't be breathing or have a pulse.
- Loss of consciousness or fainting is the most common sign of ventricular fibrillation.
Early ventricular fibrillation symptoms
It's possible that you may have other signs and symptoms that start about an hour before your heart goes into ventricular fibrillation and you faint. These include:
- Chest pain
- Rapid heartbeat (tachycardia)
- Shortness of breath
- To understand how ventricular fibrillation happens, consider what should happen during a normal heartbeat.
What's a normal heartbeat?
When your heart beats, the electrical impulses that cause it to contract must follow a precise pathway through your heart. Any interruption in these impulses can cause an irregular heartbeat (arrhythmia).
Your heart is divided into four hollow chambers. The chambers on each half of your heart form two adjoining pumps, with an upper chamber (atrium) and a lower chamber (ventricle).
During a heartbeat, the smaller, less muscular atria contract and fill the relaxed ventricles with blood. This contraction starts when the sinus node — a small group of cells in your right atrium — sends an electrical impulse causing your right and left atria to contract.
The impulse then travels to the center of your heart, to the atrioventricular node, which lies on the pathway between your atria and your ventricles. From here, the impulse exits the atrioventricular node and travels through your ventricles, causing them to contract and pump blood throughout your body.
What causes ventricular fibrillation?
It's not always known what causes ventricular fibrillation, but most cases of ventricular fibrillation begin as a rapid heartbeat called ventricular tachycardia (VT). This fast, regular beating of the heart is caused by abnormal electrical impulses that start in the ventricles. Often these are due to a problem with the electrical impulse traveling around a scar from a previous heart attack.
Most VT occurs in people with some form of heart-related problem, such as scars or damage within the ventricle muscle from a heart attack. Sometimes VT can last for 30 seconds or less (nonsustained), and not cause any symptoms, although it causes inefficient heartbeats. But, VT may be a sign of more-serious heart problems. If VT lasts more than 30 seconds, it will usually lead to palpitations, dizziness or fainting. Untreated VT will often lead to ventricular fibrillation.
In ventricular fibrillation, rapid, chaotic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood. Without an effective heartbeat, your blood pressure plummets, instantly cutting off blood supply to your vital organs — including your brain. Most people lose consciousness within seconds and require immediate medical assistance, including cardiopulmonary resuscitation (CPR). Your chances of survival are better if CPR is delivered until your heart can be shocked back into a normal rhythm with a device called a defibrillator. Without CPR or defibrillation, death results in minutes. Most cases of ventricular fibrillation are linked to some form of heart disease. Ventricular fibrillation is frequently triggered by a heart attack.
Several factors may increase your risk of ventricular fibrillation, including:
- A previous episode of ventricular fibrillation
- A previous heart attack
- A heart defect you're born with (congenital heart disease)
- Heart muscle disease (cardiomyopathy)
- Injuries that cause damage to the heart muscle, such as electrocution
- Use of illicit drugs, such as cocaine or methamphetamine
Because ventricular fibrillation is a life-threatening condition, it's unlikely you'd be diagnosed at a routine doctor's appointment unless you happened to collapse in the office. Ventricular fibrillation is always diagnosed in an emergency situation. Your doctors will know if you're in ventricular fibrillation based on results from:
- Heart monitoring. A heart monitor that will read the electrical impulses that make your heart beat will show that your heart is beating erratically, or not at all.
- Pulse check. In ventricular fibrillation, your pulse will be difficult to feel, or you may not have a pulse.
Tests to diagnose the cause of ventricular fibrillation
After your doctors diagnose and treat ventricular fibrillation, they'll want to know what caused it. You'll have additional tests to find the cause of your ventricular fibrillation, which can include:
- Electrocardiogram (ECG). This is the first test done to diagnose a heart attack, which is the most common cause of ventricular fibrillation. This test records the electrical activity of your heart via electrodes attached to your skin. Impulses are recorded as "waves" displayed on a monitor or printed on paper. Because injured heart muscle doesn't conduct electrical impulses normally, the ECG may show that a heart attack has occurred or is in progress.
- Blood tests. Certain heart enzymes slowly leak out into your blood if your heart has been damaged by a heart attack. Emergency room doctors take samples of your blood to test for the presence of these enzymes.
- Chest X-ray. An X-ray image of your chest allows your doctor to check the size and shape of your heart and its blood vessels.
- Nuclear scan. This test helps identify blood flow problems to your heart. Small amounts of radioactive material, such as thallium, are injected into your bloodstream. Special cameras can detect the radioactive material as it flows through your heart and lungs. Areas of reduced blood flow to the heart muscle — through which less of the radioactive material flows — appear as dark spots on the scan.
- Echocardiogram. This test uses sound waves to produce an image of your heart. During an echocardiogram, sound waves are directed at your heart from a transducer, a wand-like device, held on your chest. The sound waves bounce off your heart and are reflected back through your chest wall and processed electronically to provide video images of your heart.
- Coronary catheterization (angiogram). This test can show if your coronary arteries are narrowed or blocked. A liquid dye is injected into the arteries of your heart through a long, thin tube (catheter) that's fed through an artery, usually in your leg, to the arteries in your heart. As the dye fills your arteries, the arteries become visible on X-ray, revealing areas of blockage. Additionally, while the catheter is in position, your doctor may treat the blockage by performing an angioplasty, also known as coronary artery balloon dilation, balloon angioplasty and percutaneous coronary intervention. Angioplasty uses tiny balloons threaded through a blood vessel and into a coronary artery to widen the blocked area. In most cases, a mesh tube (stent) also is placed inside the artery to hold it open more widely and prevent re-narrowing in the future.
- Cardiac computerized tomography (CT) or magnetic resonance imaging (MRI). Although more commonly used to check for heart failure, these tests can be used to diagnose heart problems. In a cardiac CT scan, you lie on a table inside a doughnut-shaped machine. An X-ray tube inside the machine rotates around your body and collects images of your heart and chest. In a cardiac MRI, you lie on a table inside a long tube-like machine that produces a magnetic field. The magnetic field aligns atomic particles in some of your cells. When radio waves are broadcast toward these aligned particles, they produce signals that vary according to the type of tissue they are. The signals create images of your heart that can help your doctor determine the cause of your ventricular fibrillation.