Overview

Atrial fibrillation or AFib or AF, is the most common type of irregular heartbeat (arrhythmia). In atrial fibrillation, the two upper parts of the heart (atria) beat and quiver faster than the rest of the heart. Atrial fibrillation is associated with an increased risk of heart failure and stroke. According to the duration of the fibrillation episode, atrial fibrillation can be classified into, paroxysmal, persistent, permanent, long-standing atrial, and nonvalvular atrial fibrillation.

Until now, the main direct cause of atrial fibrillation is unclear and some cases occur for unknown reasons but it is suggested that the heart’s structure abnormalities or damage are related to atrial fibrillation, along with other factors such as elevated blood pressure, congenital heart defects which is problem with the structure of the heart that exists at birth, and lung diseases like asthma, to name a few.

The key element for atrial fibrillation is progressive fibrosis of the atria mostly caused by atrial dilation. Atrial dilation can be caused by abnormalities in the heart’s structure such as valvular heart diseases like mitral stenosis, hypertension which is elevated blood pressure, and congestive heart failure that results in fluid buildup as a result of low circulatory blood. Following a dilated atria, is the initiation of renin aldosterone angiotensin system (RAAS) that is a hormonal cascade responsible for homeostatic control of arterial pressure, that produce multiple cell signaling events such as apoptosis; programmed cell death.,

Usually, atrial fibrillation related symptoms are palpitations, tiredness, and shortness of breath, dizziness, confusion, and chest pain.

Heart disease, high blood pressure, drinking alcohol, and obesity are the most common alterable risk factors for atrial fibrillation that can be changed via practicing healthy eating habits, doing physical activity, and stopping smoking. Age and family history may also play a role. .

A pulse test is capable of detecting a suspected case of atrial fibrillation. However, to be completely sure the patient will need to undergo full medical diagnostic tests. These may include electrocardiogram with its subtypes, echocardiogram, blood tests, stress test, and chest X-ray.

Atrial fibrillation is often treated with medications to reset the rhythm of the heart, maintain a normal heart rhythm, and prevent blood clots. Blood-thinning medications such as warfarin and other anticoagulants are recommended to decrease the risk of stroke. In certain cases, surgery procedure may be conducted such as catheter ablation that uses radiofrequency energy, extreme cold (cryotherapy) or heat for destruction of hot spots(area responsible for problem)., surgical maze procedure that forms scar tissue responsible for disrupting electrical pulses causing atrial fibrillation, and atrioventricular node ablation that uses radiofrequency energy through a catheter to destroy problematic areas.

According to the Centers for Disease Control and Prevention (CDC), around 2% and 9% of people who are 65 or younger or 65 or older, respectively.

Atrial fibrillation is a quivering or irregular heartbeat in the two upper chambers (the atria), which occurs with no coordination with the two lower chambers (the ventricles) of the heart. This can increase the risk of stroke, heart failure, blood clots and other heart-related complications. It is the most common type of arrhythmia which is any change from the normal sequence of electrical impulses.

Atrial fibrillation can be classified into:

• Paroxysmal atrial fibrillation

Unusual electrical signals and rapid heart rate occur suddenly and stop on their own or with intervention, with a usual duration of 24 hours and up to 7 days. Symptoms are drastically variable, unpredictable, and can become permanent form of atrial fibrillation.  

•  Persistent atrial fibrillation

This case has a duration longer than 7 days and requires treatment in the majority of cases.

• Permanent atrial fibrillation

If the previous two cases increase in their occurrence, they become this type. Treatment cannot restore the normal rhythm of the heart.

• Long-standing atrial fibrillation

Irregular rhythm that has a duration of more than one year.

• Nonvalvular atrial fibrillation

A heart valve issue in this case is not related to atrial fibrillation.

Causes of atrial fibrillation

For some cases of atrial fibrillation, the cause is unknown.  Atrial fibrillation has an unusual passage of the electrical signals through the heart, where they become very rapid and disorganized.

Mainly, the heart's structure abnormalities or damage causes atrial fibrillation.  Other possible causes of atrial fibrillation include:

• Elevated blood pressure.
• Heart attacks.
• Coronary artery disease.
• Abnormal heart valves.
•  Congenital heart defects.
• Overactive thyroid gland or other metabolic imbalances.
• Exposure to triggers, such as medications, caffeine, tobacco or alcohol.
• Sick sinus syndrome, an improper functioning of the heart's natural pacemaker.
• Lung diseases.
• Previous heart surgery.
• Viral infections.
• Stress due to pneumonia, surgery or other illnesses.
• Sleep apnea.

The following conditions can increase the chance of developing atrial fibrillation:

• Age

The risk of developing atrial fibrillation is increased with age.

• Family history
• Genetic predisposition in some families increase the risk for atrial fibrillation.  Heart disease

Pre-existing heart diseases promote the risk of developing atrial fibrillation such as coronary artery disease, heart valve disease, rheumatic heart disease, heart failure, weakened heart muscle (cardiomyopathy), heart birth defects, and inflamed membrane or sac around the heart (pericarditis).11

• High blood pressure

High blood pressure and in particular unmanaged high blood pressure can increase the risk for atrial fibrillation.

• Drinking alcohol

Alcohol can set off atrial fibrillation. Binge drinking, which is drinking large amounts in short periods of time, t exposes an individuals to a higher risk.

• Obesity

The risk of developing atrial fibrillation is highly increased in obese people.

Atrial fibrillation has progressive fibrosis; which is a continuous build up process for excessive collagenous cellular matrix that would be able to replace a functional heart muscle, as its main event for pathogenesis and is a result of atrial dilation; enlarged atria in most cases.  Some abnormalities in the heart’s structure can cause raised pressure inside the heart, which can lead to the dilation of the atria. Such structural abnormalities include valvular heart diseases such as mitral stenosis which refers to a defect in the mitral valve apparatus that leads to an obstructed left ventricular inflow at the level of mitral valve, hypertension which is elevated blood pressure and congestive heart failure which is fluid buildup in other organs due to the inability of the heart to pump sufficient amount of circulatory blood, that leads to less blood flow into the kidneys and  less filtered fluid into urine.

Dilated atria triggers the renin aldosterone angiotensin system (RAAS); hormonal series of events that function in the homeostatic control of arterial pressure, tissue perfusion, and extracellular volume,  which is followed by an increase in deposition of matrix metalloproteinase that are responsible for degradation of most extracellular matrix proteins during organogenesis, growth and normal tissue turnover,  and disintegrin; a group of proteins extracted from viper venoms that are potent inhibitors of both platelet aggregation and integrin-dependent cell adhesion, in the atrial walls.

Later on, multiple cell signaling cascades are formed by (RAAS) that promote increased intracellular calcium,   cytokine release and inflammation, oxidative stress; increased number of oxidants compared to antioxidants, and production of growth-related factors that also stimulate fibrosis, as well as possible modulation of ion channel; responsible for regulating neuronal electrical activity and of higher neural functions,  and gap-junction dynamics; the mechanism of electrical synapse that connect neurons.

Atrial fibrillation promotes (RAAS) components such as angiotensin II, causing atrial remodeling and fibrosis, with loss of atrial muscle mass that happen in a progressive manner.  

Reactive  interstitial  fibrosis; when extra amounts of collagen is deposited in the extracellular matrix leading to a physical and an electrical separation of myocytes; contractile cell of the myocardium separates muscle bundles, whereas reparative  fibrosis; myocardium replacement with fibrous tissue in large amounts found in infarcted hearts,  replaces  dead  cardiomyocytes. These two factors promoting for fibrosis disrupt electrical continuity , leading to  slowed conduction. Fibroblasts; a connective-tissue cell responsible for producing proteins and molecular collagen that form extracellular fibrillar matrix of connective tissue, are able to join cardiomyocytes and when they are present in large numbers, they increase the chances of reentry and/or ectopic activity; normal small changes in a heartbeat . Fibrosis causes paroxysmal AF progression to permanent forms.

Signs and symptoms of atrial fibrillation

Some cases of AF are symptomless and can only be detected through physical examination or EKG (electrocardiogram). However, atrial fibrillation symptoms are:

• Palpitations, which are sensations of noticeably rapid, strong, or irregular heartbeat.
• Tiredness, weakness and reduced ability to exercise.
• Shortness of breath.
• Dizziness or feeling faint.
• Confusion.
• Chest pain and pressure.
• Sweating.

Atrial fibrillation is diagnosed by doctor through reviewing patient’s signs and symptoms, medical history, and conducting a physical examination such as testing patient’s pulse. Diagnostic investigation of atrial fibrillation typically includes:

• Electrocardiogram (ECG) or Holter monitor or event recorder

The ECG is a simple, painless and primary tool for diagnosing atrial fibrillation. Where a small electrodes are attached to the patient’s arms, legs and chest, and connected by wires to an ECG machine, to record the rhythm and electrical activity of the heart. The small electrical signals are transferred onto paper which in the case of atrial fibrillation shows an unusual pattern with beats exceeding 100 per minute. An episode of atrial fibrillation could be hard to detect, which requires wearing a portable ECG recorder (Holter monitor) that provides 24-48 hours observation or detects a sudden episode. In some cases, a portable ECG is used for prolonged periods (event recorder) that’s could last from few weeks and up to few months that is only operated when symptoms are sensed.

• Echocardiogram
• In this noninvasive an ultrasound test, sound waves, that reflect back from the heart to the chest via a transducer;  wand-like device, are used to create a moving picture of patient’s heart. It evaluates structural and functional properties of the heart and valves.  Blood clots that are formed in the heart are detected through transesophageal echocardiography that uses a flexible tube with a transducer passing into the throat until the esophagus. Echocardiogram is particularly helpful in detecting, a blocked blood supply by a heart attack, the lack of blood supply with the right pressure, congenital heart disease that disturb the normal function of the heart, heart valve problems or infections (endocarditits) that cause defective heart valves in control of regulating blood flow and the case where the heart walls are thickened or enlarged (cardiomyopathy). Contrast echocardiogram uses injection via the blood stream by a contrast agent seen on the scan, providing a detailed image of the heart. A type of echocardiogram called

Stress echocardiogram detects the heart’s activity during or after exercise, or when needed after taking an injection that increases the heart’s activity.

• Blood tests

Atrial fibrillation testing may include blood tests that check  thyroid hormones level especially hyperthyroidism which is an overactive thyroid gland, electrolytes balance; minerals that aid in maintaining fluid levels and acid-base balance in the body, anemia; the lack of iron leading to decreased red blood cells, and kidney dysfunction.

• Chest X-ray

The doctor may order a chest X-ray which is a quick and painless procedure commonly used to produce images of the inside of the body. X-ray images that detect the heart and lungs are used in diagnosing underlying conditions other than atrial fibrillation that could be responsible for symptoms, in addition to lung problems such as fluid buildup in the lungs as a result of atrial fibrillation.

Atrial fibrillation treatment depends on the severity and frequency of symptoms and on a pre-existing case of a heart disease. Treatment includes.

• Resetting heart's rhythm

• Electrical cardioversion

It uses exposure to an electrical shock with sedation via paddles or patches placed on the patient’s chest. Following that, a momentarily pause for the heart occurs to create a normal rhythm afterwards once the hearts beats again. Sometimes, preceding this process, medication is needed to induce normal sinus rhythm.  

• Cardioversion with drugs

Anti-arrhythmics drugs are used to help restore normal sinus rhythm. Intravenous or oral medications are prescribed depending on the heart’s condition. This treatment usually requires hospital monitoring and blood -thinning medication such as warfarin to decrease blood clots and stroke prior to procedure.

• Maintaining a normal heart rhythm

Following electrical cardioversion, anti-arrhythmic medications could be used to help prevent future episodes of atrial fibrillation. Medications may include:

•     Dofetilide.
•     Flecainide.
•     Propafenone.
•     Amiodarone.
•     Sotalol.

• Heart rate control

These medications work on controlling and restoring a normal heart rate and they include:

• Digoxin

This drug could be effective at rest, not during activity.

Alternative medications these include beta blockers and calcium channel blockers which both reduce blood pressure and are taken along with digoxin.

• Catheter and surgical procedures

When medications or cardioversion fail to control atrial fibrillation, certain procedures are used to eliminate the problematic area such as:

• Catheter ablation

This method is used in patients with a normal heart but are with atrial fibrillation caused by hot spots, which are rapidly discharging triggers.

In catheter ablation, a doctor inserts thin, soft wires called catheters , where they insert into the groins, to pass through to the blood vessels and into the heart and have electrodes at their tips which uses radiofrequency energy, extreme cold (cryotherapy) or heat for destruction of hot spots.

• Surgical maze procedure

This is used during open-heart surgery by making certain patterns of scar tissue with a scalpel, radiofrequency or cryotherapy, in the upper chambers of the heart. Although high rates of success were linked to this technique, atrial fibrillation may recur and in such case other treatments such as catheter ablation are needed. Scar tissue is known to not carry electricity, which makes it disrupt electrical pulses causing atrial fibrillation. The patient is exposed to surgical maze procedure if the patient does not respond to other treatment procedures, or he/she has other necessary heart surgery, such as coronary artery bypass surgery or heart valve repair because the surgical maze procedure requires open-heart surgery. 

• Atrioventricular (AV) node ablation

This is used when  other treatment procedures if medications or other forms of catheter ablation do not work, or if the patient had side effects or does not make a good candidate for other procedures.

The pathway connecting the upper chambers (atria) and lower chambers (ventricles) of the heart (AV node) is targeted by radiofrequency energy through a catheter to destroy this small area of tissue.

After this procedure, the ventricles stop receiving electrical impulses from atria, but the atria continue to fibrillate. A pacemaker, in addition to blood- thinning medications are required after this in order to, maintain   a normal beat of the ventricles and to reduce the risk of stroke because the heart rhythm is still atrial fibrillation, respectively.

• Preventing blood clots

• Anticoagulants

This drug is prescribed as blood-thinning medications, it include:

• Warfarin

Warfarin is an anticoagulant, which means it stops the blood from clotting. It should be taken under the doctor’s instructions, because warfarin is a powerful medication that may cause dangerous bleeding. If the patient is prescribed warfarin, regular blood tests are needed.

• Newer anticoagulants

These blood-thinning medications are shorter acting than warfarin and do not require monitoring. Besides, these medications do not suit people who have mechanical heart valves. Following exact instructions for such medications is essential.

• Dabigatran

This anticoagulant medication is as efficient as warfarin in preventing blood clotting. No blood tests are needed to check for the proper dose. People with mechanical valves can’t use this drug.

• Rivaroxaban

An anticoagulant medication with the same efficiency as warfarin in preventing strokes. It should be used upon under a doctor’s supervision and prescription.

• Apixaban

It prevents strokes the same as warfarin.

• Left atrial appendage closure

The perfect candidates for this procedure are people with no valve problems, who have a high risk of blood clots and bleeding, and those who can’t take anticoagulants to begin with or anticoagulant were not effective for them.

This procedure involves the insertion of a catheter into a vein in the leg, until it reaches the right atrium, where a small incision is made to allow the catheter pass to the left atrium. Finally, a device named a left atrial appendage closure is inserted into the catheter to close a small sac (appendage) in the left atrium.

Since most clots are formed in the left atrial appendage in atrial fibrillation cases, this procedure lowers the risk of blood clotting.  

Atrial fibrillation has two major complications:

• Stroke

Not all of the blood is pumped into the ventricles, instead some blood accumulates in the atria, in atrial fibrillation. This accumulation could cause blood clots. When this clot moves into the brain it causes a stroke. This fact makes blood-thinning medicines essential in treating AF.

The risk of developing a stroke depends on a number of factors, such as age (more likely to occur with age), high blood pressure, diabetes, a history of heart failure or previous stroke, and other factors.

• Heart failure

Uncontrolled atrial fibrillation may weaken the heart muscle and lead to heart failure; when not enough blood is pumped into the body. Heart failure can be treated via lifestyle changes, medicines, and procedures or surgery. 

As with other cardiovascular diseases, a therapeutic lifestyle changes (TLC) diet can be introduced as an effective preventive action against atrial fibrillation. (TLC) diet involves:

• Eating healthy food that includes a variety of whole grains, fruits, and vegetables daily, and eliminate saturated fat, Trans fat, and cholesterol from the consumed diet.
• Decreasing the use of sugar-sweetened beverages and sweets.

-  Following the DASH diet which is helpful in lowering the blood pressure.

- Maintaining cholesterol and triglycerides at healthy levels with dietary changes and medicines, if prescribed.

Other lifestyle changes include:

• Doing physical activity such as swimming, running and walking and preferable on daily basis.
• Weight loss and maintaining body weight within its healthy range.
• Stop smoking, as reported in a study published in an American journal, Heart Rhythm, smoking is associated to AF by two-folds in current smokers.

-Men at age 65 and younger are allowed two drinks a day.  People of age 65 and older should not consume more than one drink a day. Overall, limiting or avoiding alcohol should be taken into consideration.

-Get ongoing medical care and take the medicines as prescribed.

- Limit caffeine intake.

- Reduce stress, which is a trigger for heart rhythm problems.

-Over-the-counter medications should be cautiously used.

Ongoing medical care is important and helps atrial fibrillation patients live normal, active lives. However, atrial fibrillation is related to increased morbidity and mortality, as a result of thromboembolic disease risk, especially stroke.

According to the American Centers for Disease Control and Prevention (CDC), around 2% of people who are 65 or younger have atrial fibrillation, and around 9% of adults aged65 or older have atrial fibrillation. The incidence rate of atrial fibrillation is higher among women, because women usually live longer than men and atrial fibrillation cases increase with age.