Atrial fibrillation is a condition in which disruption of atrial activity results in loss of effective atrial contraction. The heart beats at a frequency of 350 to 600 beats per minute. These fast, irregular impulses travel through atrioventricular node of heart into ventricles and result in a rapid and "irregular" ventricular response. There are paroxysmal and persistent forms.Causes of atrial fibrillation
Risk factors for developing atrial fibrillation include:
Atrial fibrillation is caused by activation of multiple return circuits, or "waves," around atrial myocardium. They are usually caused by a quick focus of fire. Conduction of atrial impulses to ventricles is variable and unpredictable. Only a few impulses pass through AV node, causing an irregular ventricular response. The wavelength plays a crucial role in pathogenesis of AF. Increasing wavelength prevents or stops autofocus. It may be caused by antiarrhythmic drugs.
Due to uncoordinated atrial depolarization in different parts of atria in atrial fibrillation, blood flow in upper chambers of heart does not flow properly, and these chambers are prone to blood clots. These clots can then travel to ventricles, from right heart to lungs, and from left ventricle to general circulation. Sometimes a blood clot moves away from atria, causing a stroke.Symptoms and signs
Symptoms of atrial fibrillation (AF) include palpitations, irregular heartbeat, shortness of breath, chest discomfort, dizziness, and fainting. Many patients feel weak and intolerant to physical activity, which leads to a weakening of contractility of heart. The awareness of a fast and/or irregular heartbeat can also lead to anxiety. Systemic embolism can provoke or exacerbate heart failure.
Patients with healthy hearts tolerate atrial fibrillation better. People with underlying heart disease often find it harder to tolerate atrial fibrillation without complications. Once symptoms of atrial fibrillation develop, they can become more severe as this indicates that heart is not pumping enough blood to body.
The ventricular rate depends on degree of atrioventricular block, but a rapid ventricular response may occur with 1:1 conduction. Carotid sinus massage or adenosine may increase degree of obstruction and aid in diagnosis.Complications
Atrial fibrillation can be suspected as soon as a pulse is felt, but a full medical examination is required for a complete diagnosis.ECG
One of most important tests is electrocardiogram (ECG), which can also provide evidence of any prior heart disease that may have caused condition. If AF is intermittent, patient may need to wear a Holter monitor for an extended period of time to record one or more episodes of AF. ECG and Holter are often used in conjunction with a chest x-ray and echocardiogram, which show walls of heart as it contracts. ECG functions in AF include:
Fast atrial fibrillation can be difficult to distinguish from other tachycardias. However, RR intervals remain irregular and overall ratio fluctuates frequently. Drawing an R wave on a piece of paper or using a caliper usually confirms diagnosis.Image
A chest x-ray in young patients may indicate presence of congenital heart disease. In older patients, it can provide information about size of heart and presence of heart failure. Echocardiography is useful in excluding thrombosis and determining diameter of left atrium (>4.5 cm).blood analysis
Routine blood tests are also helpful in diagnosis. They can present with anemia, which can be a complex condition, impaired kidney function, or an overactive thyroid gland (thyroid toxicity).treatment
Without treatment, an overactive heart muscle weakens and stretches. This makes it difficult for atria to contract normally, so more blood flows back. This problem not only increases risk of stroke, but can also lead to congestive heart failure. Properly treating atrial fibrillation is best way to reduce your risk of stroke. Patients with persistent, persistent, or recurrent paroxysmal AF should be treated. AF treatment plan goals:
Aspirin or warfarin is often prescribed to reduce risk of stroke. Aspirin is antiplatelet and less likely to cause abnormal bleeding, but warfarin appears to be more effective in preventing strokes caused by blood clots. Periodic INR tests are done to control dose of warfarin. The INR should usually be tested between 2.0 and 3.0.
The administration of warfarin or aspirin to a patient depends on risk factors for thromboembolism. This can be determined by assessing patient on CHADS 2 scale.
Patients with a low score (0) can take 325 mg of aspirin daily to prevent blood clotting. Those with an average score (1-2 points) may take aspirin or warfarin, depending on patient's preference. Individuals with a high CHADS score of 2 (3 or more) should receive warfarin prophylaxis to maintain an INR of 2.0–3.0 unless contraindicated (eg, history of falls, clinically significant gastrointestinal bleeding, failure to undergo routine INR screening ).2. Heart rate control
Cardioversion returns abnormal heart rate to a normal rate. Cardioversion can be done with medication or electricity.
Based on Affirmative, Race, and Staf studies, anticoagulant therapy is preferred. Rhythm control (cardioversion) in asymptomatic patients does not affect survival. Electrical or chemical cardioversion may be required in symptomatic cases or in emergency situations such as cardiovascular instability and heart failure.
Medications include amiodarone, dofetilide, dioxypyramide, flecainamide, and procainamide.
Electrocardioversion is commonly used to treat persistent or persistent AF, often with medical treatment.
There are two types of electrical cardioversion: external and internal. For external cardioversion, two external paddles are placed on patient's chest or chest and back. A high-energy electrical discharge is delivered through patch and body to heart, which brings heart out of atrial fibrillation and restores a normal rhythm.
Internal cardioversion uses a similar approach, but instead of paddles outside body, a catheter is inserted through a vein into heart. Electrical energy is sent through catheter into heart to stop atrial fibrillation. Internal cardioversion has achieved high success rates and represents an alternative to external cardioversion.4. Ablation
Heart ablation is a medical procedure that prevents abnormal electrical impulses from occurring in first place. During ablation, electrophysiologist first performs a mapping, which means that exact area in heart where abnormal signal starts is at tip of needle. The electrophysiologists then removed small patches of tissue that caused arrhythmia.
There is also a procedure called AV node ablation. This involves removing AV node, which prevents abnormal impulses from reaching lower chambers of heart. After this treatment, a pacemaker is used to regulate heartbeat.5. AF suppression
Atrial Fibrillation Suppressor is designed to suppress atrial fibrillation (AF). An implanted pacemaker stimulates heart in such a way that it precedes any irregular rhythm.
A clinical study has shown that a software-based atrial fibrillation suppression algorithm suppresses symptomatic paroxysmal and persistent atrial fibrillation better than standard pacing. In some ICDS and pacemakers manufactured by St. Jude Medical has an AF suppression algorithm available.Forecast and survival
The prognosis depends on underlying cause: a good prognosis for idiopathic atrial fibrillation and a poor prognosis for ischemic cardiomyopathy. A healthy lifestyle, regular blood pressure checks, and treatment for high blood pressure can reduce occurrence of heart problems that lead to atrial fibrillation.Some results of study
Study shows that women are more likely than men to form dangerous blood clots in patients with atrial fibrillation who are not taking anticoagulant drug warfarin. Another study found that men who were angry or expected worst were more likely to develop an irregular heart rhythm called atrial fibrillation.Links
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2. Go As, Hylek EM, Phillips Ka et al. (2001). "Adult atrial fibrillation diagnostic rates: national implications for rhythm control and stroke prevention: anticoagulant therapy and risk factors in atrial fibrillation (atrial) study". JAMA 285(18):2370-5.
3. Go As, Hylek EM, Phillips Ka, Chang Y, Henault le, Selby JV, Singer DE (2001). "Adult atrial fibrillation diagnostic rates: national implications for rhythm control and stroke prevention: anticoagulant therapy and risk factors in atrial fibrillation (atrial) study". JAMA 285(18):2370-5.
4. Gage B.F., Waterman A.D., Shannon W., Behler M., Rich M.W., Radford M.J. (2001). "Confirmation of a clinical classification scheme for stroke prediction: findings from National Atrial Fibrillation Registry". JAMA 285(22):2864-70.