During atrial fibrillation, the heart's two small upper chambers called the atria, quiver instead of beating effectively. That’s why blood isn't pumped out of them completely so it may pool and clot. If a piece of a blood clot in the atria leaves the heart and becomes lodged in an artery in the brain, it can lead to a stroke.
Incidence
Atrial fibrillation is the most common cardiac arrhythmia. More than 2 million Americans have this condition, which can cause palpitations, shortness of breath, fatigue and a stroke. The condition is increasingly common with advancing age. It affects less than 1 percent of Americans younger than 60, but as many as one in 10 people older than 80. Overall, approximately 15-25% of all the strokes in the United States can be attributed to atrial fibrillation.
Risk factors
Known risk factors include:
- male sex
- valvular heart disease
- rheumatic valvular disease
- CHF
- hypertension
- diabetes
Additional risk factors, such as advanced age and prior history of stroke, place patients with preexisting atrial fibrillation at even higher risk for further complications such as stroke.
Signs and symptoms of atrial fibrillation
It is clear that a heart in atrial fibrillation simply doesn't beat efficiently which means that it may not be able to pump an adequate amount of blood which leads to a drop in blood pressure.
People with atrial fibrillation experience:
- Palpitations, which are sensations of a racing, uncomfortable, irregular heartbeat or a flopping in your chest
- Weakness
- Lightheadedness
- Shortness of breath
- Chest pain
However, some people with atrial fibrillation have no symptoms and are unaware of their condition until their doctor discovers it during some regular physical examination.
Normal anatomy of the heart and mechanism of the condition
A heart normally consists of four chambers, two upper chambers called atria and two lower chambers called ventricles. Within the upper right chamber there is a specific group of cells called the sinus node which represent a natural heart's pacemaker. The sinus node produces the impulse that starts each heartbeat. During a normal rhythm, the impulse travels first through the atria, then through a connecting pathway between the upper and lower chambers called the atrioventricular node.
What happens in atrial fibrillation? In atrial fibrillation, the atria are affected by chaotic electrical signals. As a result, they quiver. Another result is that the ventricles also beat rapidly, but not as rapidly as the atria. This leads to the irregular and fast heart rhythm that affects both atria and ventricles. The heart rate in atrial fibrillation may range from 100 to 175 beats a minute. The normal range for a heart rate is 60 to 100 beats a minute.
Possible causes of atrial fibrillation
The most common cause of atrial fibrillation is defiantly abnormality in the heart's structure. Many diseases that could affect the heart's valves or pumping system such as long-term high blood pressure are also likely causes . However, some people who have atrial fibrillation don't have any underlying heart disease, and the cause is unknown.
Other possible causes of atrial fibrillation include:
- High blood pressure
- Abnormal heart valves
- Congenital heart defects
- An overactive thyroid or other metabolic imbalance
- Exposure to heart stimulants, such as caffeine or tobacco, or to alcohol
- Sick sinus syndrome — this occurs when the heart's natural pacemaker stops functioning properly
- Emphysema or other lung diseases
- Heart surgery
- Coronary artery disease
- Hypertrophic cardiomyopathy
- Previous heart surgery
- Viral infections
- Stress due to pneumonia, surgery or other illnesses
Classification of atrial fibrillations
The American Heart Association have proposed the following classification system based on simplicity and clinical relevance:
First Detected
Any patient newly diagnosed with atrial fibrillation fits in this category, as the exact onset and chronicity of the disease is often uncertain.
Recurrent
Any patient with 2 or more identified episodes of atrial fibrillation is said to have recurrent atrial fibrillation. This is further classified into paroxysmal and persistent based on when the episode terminates without therapy.
Paroxysmal
Atrial fibrillation is said to be paroxysmal when it terminates spontaneously within 7 days, most commonly within 24 hours.
Persistent
Persistent or chronic atrial fibrillation is atrial fibrillation established for more than seven days. Differentiation of paroxysmal from chronic or established atrial fibrillation is based on the history of recurrent episodes and the duration of the current episode of the condition.
Lone atrial fibrillation
Lone atrial fibrillation is defined as atrial fibrillation in the absence of clinical findings. Patients with this condition who are under 65 have the best prognosis.
Risk factors
There are several risk factors that could be linked to atrial fibrillation and the most common are:
Age
The older you are, the greater your risk of atrial fibrillation. As you age, the electrical and structural properties of the atria can change. This may lead to the breakdown of the normal atrial rhythm.
Other heart diseases
Anyone with heart disease faces an increased risk of atrial fibrillation.
Other conditions
It is proven that people with thyroid problems, diabetes and high blood pressure have an elevated risk of atrial fibrillation.
Obesity
It is considered that obesity also may play an important role in the development of atrial fibrillation.
Diagnosis of atrial fibrillation
Electrocardiogram
Atrial fibrillation is best diagnosed with an electrocardiogram, an investigation performed routinely whenever irregular heart beat is suspected. Characteristic findings are:
- absence of P waves
- unorganized electrical activity in their place
- irregularity of R-R interval due to irregular conduction of impulses to the ventricles
Holter monitor testing
This is a portable version of an ECG which is being used to monitor patient’s heart activity for 24h. It's especially useful in diagnosing rhythm disturbances that occur at unpredictable times. Patient wears the monitor under clothing.
Echocardiogram
This is a very good and effective diagnostic tool. In this test, the sound waves are used to produce a video of patient’s heart. Sound waves are directed at heart from a wand-like device called transducer that's held on the patient’s chest. The sound waves that bounce off the patient’s heart are reflected back through the chest wall and processed electronically to provide video images of heart in motion.
Blood tests
These blood tests can help a doctor rule out thyroid problems or blood chemistry abnormalities that may lead to atrial fibrillation.
Possible complications of atrial fibrillation
There are two possible and very dangerous complications of atrial fibrillation. These are:
Stroke
The fact is that the chaotic rhythm may cause blood to pool in your atria and form clots. These blood clots could dislodge from the heart and travel to the brain. There they might block the blood flow, causing a stroke. A blood clot can also lodge in other blood vessels, such as those supplying the kidneys or legs.
Congestive heart failure
Atrial fibrillation alone may weaken the heart, leading to heart failure.
This is a condition in which a patient’s heart can't circulate enough blood to meet the body's needs.
Treatment of atrial fibrillation
Treatments for atrial fibrillation include medications and procedures that regulate the heart rhythm. The most important goals of treating atrial fibrillation include:
- Restoring the heart to a normal rhythm (rhythm control)
- Slowing the heart rate (rate control)
- Preventing blood clots
Restoring the heart to a normal rhythm
In order to correct atrial fibrillation doctors often perform a procedure called cardioversion which can be done on two ways:
Medications
Medications called anti-arrhythmics, which are designed to stop the atria's quivering and restore normal sinus rhythm, are commonly used. Some of the most common are: amiodarone (Cordarone, Pacerone), propafenone (Rythmol), procainamide (Procanbid), sotalol (Betapace) and dofetilide (Tikosyn).
Electrical cardioversion
In this short procedure an electrical shock is delivered to patient’s heart through patches placed on his or hers chest. The fact is that the shock stops heart's electrical activity for a split second. And when it begins again, it may resume the normal rhythm.
Slowing the heart rate
In the situations when atrial fibrillation can't be converted, the goal is to slow the heart rate and in order to do that the doctors are prescribing a medication called digoxin (Lanoxin). It can control the heart rate at rest but is not as effective during activity.
Preventing blood clots
When someone is at especially high risk of stroke, doctor may prescribe blood-thinning medications called anticoagulants, such as warfarin (Coumadin) or Aspirin.
Non-drug treatment
- AV nodal ablation with pacemaker implantation
- Maze procedure
- Pacemaker implantation
- Pulmonary vein ablation