Ventricular fibrillation overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sahar Memar Montazerin, M.D.[2]
Overview
Ventricular fibrillation (V-fib or VF) is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. As a result, the heart fails to adequately pump blood and hypoxia will occur followed by unconsciousness within 20 - 30 seconds. Ventricular fibrillation is the most commonly identified arrythmia in cardiac arrest patients. While there is some activity, the layperson is usually unable to detect it by palpating (feeling) the major pulse points of the carotid and femoral arteries. Such an arrhythmia is only confirmed by electrocardiography. Ventricular fibrillation is a medical emergency that requires prompt Basic Life Support interventions. If this arrhythmia continues for more than a few seconds, it will likely degenerate further into asystole ("flatline"). This condition results in cardiogenic shock and cessation of effective blood circulation. As a consequence, sudden cardiac death (SCD) will result in a matter of minutes. If the patient is not revived after a sufficient period (within roughly 5 minutes at room temperature), the patient could sustain irreversible brain damage and possibly become brain dead due to the effects of cerebral hypoxia. On the other hand, death often occurs if normal sinus rhythm is not restored within 90 seconds of the onset of VF, especially if it has degenerated further into asystole.
Historical Perspective
Lyman Brewer suggests that the first recorded incident of ventricular fibrillation dates as far back as 1500 BC, and can be found in the Ebers papyrus of ancient Egypt. The extract recorded 3500 years ago may even date from as far back as 3500 BC. It states: "When the heart is diseased, its work is imperfectly performed: the vessels proceeding from the heart become inactive, so that you cannot feel them, if the heart trembles, has little power and sinks, the disease is advanced and death is near." A book authored by Jo Miles suggests that it may even go back farther. Tests done on frozen remains found in the Himalayas seemed fairly conclusive that the first known case of ventricular fibrillation dates back to at least 2500 BC. Whether this is a description of ventricular fibrillation is debatable. The next recorded description occurs 3000 years later and is recorded by Vesalius, who described the appearance of "worm-like" movements of the heart in animals prior to death.
Pathophysiology
Ventricular fibrillation is a cause of cardiac arrest and sudden cardiac death. The ventricular muscle twitches randomly rather than contracting in a coordinated fashion (from the apex of the heart to the outflow of the ventricles), and so the ventricles fail to pump blood into the arteries and systemic circulation. Ventricular fibrillation is a sudden lethal arrhythmia responsible for many deaths in the Western world, and it is mostly caused by ischemic heart disease. While most episodes occur in diseased hearts, others can afflict normal hearts as well. Despite considerable research, the underlying nature of ventricular fibrillation is still not completely understood.
Causes
The heart pumps blood to the lungs, brain, and other organs. Interruption of the heartbeat for only a few seconds can lead to fainting (syncope) or cardiac arrest. Fibrillation is an uncontrolled twitching or quivering of muscle fibers (fibrils). When it occurs in the lower chambers of the heart, it is called ventricular fibrillation. During ventricular fibrillation, blood is not pumped from the heart. Sudden cardiac death results. The most common cause of VF is a heart attack. However, VF can occur whenever the heart muscle does not get enough oxygen.
Epidemiology and Demographics
Sudden cardiac arrest is the leading cause of death in the industrialized world. It exacts significant mortality with approximately 70,000 to 90,000 sudden cardiac deaths each year in the United Kingdom, and survival rates are only 2%. The majority of these deaths are due to ventricular fibrillation secondary to myocardial infarction, or "heart attack". During ventricular fibrillation, cardiac output drops to zero, and, unless remedied promptly, death usually ensues within minutes.
Risk Factors
Most people with VF have no history of heart disease. Yet they often have risk factors for heart disease, such as smoking, high blood pressure, and diabetes.
Natural History, Complications and Prognosis
VF will lead to death within a few minutes unless it is treated quickly and effectively. Even then, long-term survival for people who live through a VF attack outside of the hospital is between 2% and 25%. People who have survived VF may be in a coma or have long-term damage.
Diagnosis
History and Symptoms
A person who has a VF episode can suddenly collapse or become unconscious because the brain and muscles have stopped receiving blood from the heart.
Electrocardiogram
The electrocardiographic findings in ventricular fibrillation comprise of poorly identifiable QRS complexes and absent P waves. The heart rate is >300 beats per minute and it is irregular. The pattern is bizarre with a wandering baseline.
X-ray
There are no x-ray findings associated with ventricular fibrillation.
Electrocardiography and Ultrasound
There are no electrocardiography/ultrasound findings associated with ventricular fibrillation.
CT Scan
There are no CT scan findings associated with ventricular fibrillation.
MRI
There are no MRI findings associated with ventricular fibrillation.
Other Imaging Findings
There are no other imaging findings associated with ventricular fibrillation.
Other Diagnostic Studies
There are no other diagnostic Studies associated with ventricular fibrillation.
Treatment
Medical Therapy
In the event of cardiac arrest due to ventricular fibrillation, the immediate implementation of ACLS guidelines is indicated. When a sudden cardiac arrest occurs, immediate CPR is a vital link in the chain of survival. Another important link is early defibrillation, which has improved greatly with the widespread availability of AEDs. It often starts with analyzing the patient's heart rhythms with a manual defibrillator.
Surgery
In patients at high risk of ventricular fibrillation, the use of an implantable cardioverter defibrillator has been shown to be beneficial.
Primary Prevention
An implantable cardioverter defibrillator (ICD) is a device that can be implanted in the chest wall of people who are at risk for this serious rhythm disorder. The ICD can help prevent sudden cardiac death by quickly sending an electrical shock when ventricular fibrillation occurs. Template:WH Template:WS