Atrial Fibrillation – Description, Causes, and Treatment.

Description – Atrial Fibrillation

Atrial fibrillation is an irregular and often rapid heart rate that can increase your risk of strokes, heart failure, and other heart-related complications.

During atrial fibrillation, the heart’s two upper chambers (the atria) beat chaotically and irregularly — out of coordination with the two lower chambers (the ventricles) of the heart. Atrial fibrillation symptoms often include heart palpitations, shortness of breath and weakness.

Episodes of atrial fibrillation may come and go, or you may develop atrial fibrillation that doesn’t go away and may require treatment. Although atrial fibrillation itself usually isn’t life-threatening, it is a serious medical condition that sometimes requires emergency treatment.

A major concern with atrial fibrillation is the potential to develop blood clots within the upper chambers of the heart. These blood clots forming in the heart may circulate to other organs and lead to blocked blood flow (ischemia).

Pathophysiology

The pathogenesis of AF can be broadly divided into the categories of triggers, substrate, and sustaining mechanisms. Since the late 1990s, it has been recognized that the initiation of AF can occur because of premature atrial contractions triggered by beats that arise from the pulmonary veins (PVs), usually from muscular tissue sleeves near the junction with the left atrium. These triggers may also fire repetitively and contribute to the maintenance of AF, essentially becoming drivers of AF. Focal triggers outside the PV including posterior left atrial, ligament of Marshall, coronary sinus, venae cavae, septum, and left atrial appendage to contribute to the disease process. Focal triggers, especially the PVs, are felt to be very important early in the disease process and, in particular, among patients with paroxysmal AF.

Over time, myocardial fibrosis develops within the atrial tissue in association with AF to support its maintenance by shortening affected tissue refractory periods. Myocardial fibrosis of the atrium seems to be the common feature of the progression of AF disease state. This has led to the adage that AF begets AF. Once AF is initiated by focal triggers, several theories have been postulated to explain the maintenance of AF. They include the multiple wavelet model, AF rotors and the role of the autonomic nervous system. The multiple wavelet model has suggested that AF is sustained by multiple simultaneous wavelets meandering throughout the atria. Atrial tissue with abnormal electrical propagation recorded by mapping catheters has been referred to as complex fractionated electrograms. Expression of specific connecting protein channels at the cellular level is also felt to be an important contributor to the disease substrate and sustaining mechanisms. Contemporary understanding of the AF substrate and sustaining mechanisms now also includes the role of the autonomic nervous system and, more recently, the discovery and evaluation of the concept of AF rotors.

What causes atrial fibrillation?

It’s not known exactly what causes AF, but it’s more common in people with other heart conditions or risk factors like:

It can also be associated with other health conditions including:

• Asthma
• Lung cancer
• Pulmonary embolism.

Many people won’t have any pre-existing conditions or risk factors but will still develop AF.

When no cause can be identified, it’s known as lone atrial fibrillation.

Some people with atrial fibrillation also have an atrial flutter. If this is the case, you may experience periods of atrial flutter followed by periods of atrial fibrillation.

What are the risk factors for AFib?

The risk for AFib increases with age. High blood pressure, the risk for which also increases with advancing age, accounts for about 1 in 5 cases of AFib.

Risk factors for AFib include

• Advancing age
• High blood pressure
• Obesity
• European ancestry
• Diabetes
• Heart failure
• Ischemic heart disease
• Hyperthyroidism
• Chronic kidney disease
• Moderate to heavy alcohol use
• Smoking

Enlargement of the chambers on the left side of the heart

Atrial fibrillation symptoms

You might not experience any symptoms if you have atrial fibrillation.

Those who do experience symptoms may notice:

Heart palpitations (feeling like your heart is skipping a beat, beating too fast or hard, or fluttering)

• Chest pain
• Fatigue
• Shortness of breath
• Weakness
• Lightheadedness
• Dizziness
• Fainting
• Confusion
• Intolerance to exercise

These symptoms can come and go based on the severity of your condition.

For example, paroxysmal AFib is a type of atrial fibrillation that resolves on its own without medical intervention. But you may need to take medication to prevent future episodes and potential complications.

Overall, you might experience symptoms of AFib for several minutes or hours at a time. Symptoms that continue over several days could indicate chronic AFib.

Complications

A-fib can cause potentially life-threatening health issues.

Blood clots

• Blood can pool in the atria if the heart is not beating regularly. Blood clots can form in the pools.
• A segment of a clot, called an embolus, might break off and travel to different parts of the body through the bloodstream and cause blockages.
• An embolus can restrict blood flow to the kidneys, intestine, spleen, brain, or lungs. A blood clot can be fatal.

Stroke

A stroke occurs when an embolus blocks an artery in the brain and reduces or stops blood flow to part of the brain.

The symptoms of a stroke vary depending on the part of the brain in which it occurs. They can include weakness on one side of the body, confusion, and vision problems, as well as speech and movement difficulties.

Stroke is a key cause of disability in the U.S. and the fifth most common cause of death, according to the CDC.

Heart failure

A-fib can lead to heart failure, especially when the heart rate is high. When the heart rate is irregular, the amount of blood flowing from the atria to the ventricles varies for each heartbeat.

The ventricles may therefore not fill up before a heartbeat. The heart fails to pump enough blood to the body, and the amount of blood waiting to circulate the body instead builds up in the lungs and other areas.

A-fib can also worsen the symptoms of any underlying heart failure.

Cognitive problems

A study in the Journal of the American Heart Association showed people with A-fib have a higher long-term risk of cognitive difficulties and dementia that have no link to reduced blood flow in the brain.

How is atrial fibrillation diagnosed?

Atrial fibrillation can be chronic and sustained, or brief and intermittent (paroxysmal). Paroxysmal atrial fibrillation refers to intermittent episodes of AF lasting, for example, minutes to hours. The rate reverts to normal between episodes. In chronic, sustained atrial fibrillation, the atria fibrillate all of the time. Chronic, sustained atrial fibrillation is not difficult to diagnose. Doctors can hear the rapid and irregular heartbeats using a stethoscope. Abnormal heartbeats also can be felt by taking a patient’s pulse and by a doctor’s diagnosis.

Tests to diagnose atrial fibrillation

EKG (electrocardiogram): An electrocardiogram (EKG or ECG) is a brief recording of the heart’s electrical discharges. The irregular EKG tracings of AF are easy to recognize provided AF occurs during the EKG.

Echocardiography: Echocardiography uses ultrasound waves to produce images of the chambers and valves and the lining around the heart (pericardium). Conditions that may accompany AF such as mitral valve prolapse, rheumatic valve diseases, and pericarditis (inflammation of the “sack” surrounding the heart) can be detected with echocardiography. Echocardiography also is useful in measuring the size of the atrial chambers. Atrial size is an important factor in determining how a patient responds to treatment for the disease. For instance, it is more difficult to achieve and maintain a normal rhythm in patients with enlarged atria.

Transesophageal echocardiography (TEE): Transesophageal echocardiography (TEE) is a special echocardiographic technique that involves taking pictures of the atria using sound waves. A special probe that generates sound waves is placed in the esophagus (the food pipe connecting the mouth to the stomach). The probe is located at the end of a long flexible tube that is inserted through the mouth into the esophagus. This technique brings the probe very close to the heart (which lies just in front of the esophagus). Sound waves generated by the probe are bounced off the structures within the heart, and the reflected sound waves are used to form a picture of the heart. TEE is very accurate for detecting blood clots in the atria as well as for measuring the size of the atria.

Holter monitor: If episodes of the disease occur intermittently, a standard EKG performed at the time of a visit to the doctor’s office may not show AF. Therefore, a Holter monitor, a continuous recording of the heart’s rhythm for 24 hours, often is used to diagnose intermittent episodes of AF.

Patient-activated event recorder: If the episodes of atrial fibrillation are infrequent, a 24-hour Holter recording may not capture these sporadic episodes. In this situation, the patient can wear a patient-activated event recorder for 1 to 4 weeks. The patient presses a button to start the recording when he or she senses the onset of irregular heartbeats or symptoms possibly caused by AF. The doctor then analyzes the recordings later.

Other tests: High blood pressure and signs of heart failure can be ascertained (determined) during a physical examination of the patient. Blood tests are performed to detect abnormalities in blood oxygen and carbon dioxide levels, electrolytes, and thyroid hormone levels. Chest X-rays reveal enlargement of the heart, heart failure, and other diseases of the lung. Exercise treadmill testing (a continuous recording of the EKG during exercise) is a useful screening study for detecting severe coronary disease in a doctor’s office or hospital.

Treatments

Treatments for atrial fibrillation include medicines to control heart rate and reduce the risk of stroke, and procedures such as cardioversion to restore normal heart rhythm.

It may be possible for you to be treated by a GP, or you may be referred to a heart specialist (a cardiologist).

Some cardiologists, known as electrophysiologists, specialize in the management of abnormalities of heart rhythm.

You’ll have a treatment plan and work closely with your healthcare team to decide the most suitable and appropriate treatment for you.

Factors that will be taken into consideration include:

• Your age
• Your overall health
• The type of atrial fibrillation you have
• Your symptoms
• Whether you have an underlying cause that needs to be treated

The first step is to try to find the cause of the atrial fibrillation. If a cause can be identified, you may only need treatment for this.

For example, if you have an overactive thyroid gland (hyperthyroidism), medicine to treat it may also cure atrial fibrillation.

If no underlying cause can be found, the treatment options are:

• Medicines to reduce the risk of a stroke
• Medicines to control atrial fibrillation
• cardioversion (electric shock treatment)
• Catheter ablation
• Having a pacemaker fitted

You’ll be promptly referred to your specialist treatment team if 1 type of treatment fails to control your symptoms of atrial fibrillation and more specialized management is needed.

Medicines to control atrial fibrillation

Medicines called anti-arrhythmic can control atrial fibrillation by:

• Restoring a normal heart rhythm
• Controlling the rate at which the heartbeats

The choice of anti-arrhythmic medicine depends on the type of atrial fibrillation, any other medical conditions you have, side effects of the medicine chosen, and how well the atrial fibrillation responds.

Some people with atrial fibrillation may need more than 1 anti-arrhythmic medicine to control it.

Restoring a normal heart rhythm

A variety of medicines are available to restore normal heart rhythm, including:

• Flecainide
• Beta-blockers, particularly sotalol

An alternative medicine may be recommended if a particular medicine does not work or the side effects are troublesome.

Newer medicines are in development, but are not widely available yet.

Controlling the rate of the heartbeat

The aim is to reduce the resting heart rate to under 90 beats per minute, although in some people the target is under 110 beats per minute.

A beta-blocker, such as bisoprolol or atenolol, or a calcium channel blocker, such as verapamil or diltiazem, will be prescribed.

A medicine called digoxin may be added to help control the heart rate further.

Normally, only 1 medicine will be tried before catheter ablation is considered.

Reduce your risk of stroke

Most people need a type of blood-thinner medication (such as warfarin, apixaban, rivaroxaban or dabigatran) to reduce the risk of clotting. With warfarin, frequent blood checks are needed to monitor effectiveness and dose, but this is not required for the newer blood thinners, says Calkins. Medication decisions are based on the assessment of your stroke risk. Most patients with AF who are over age 65 require a blood thinner, Calkins says.

Prevention and Risk Reduction

Although no one is able to absolutely guarantee that a stroke or a clot can be preventable, there are ways to reduce risks for developing these problems.

After a patient is diagnosed with atrial fibrillation, the ideal goals may include:

• Restoring the heart to a normal rhythm (called rhythm control)
• Reducing an overly high heart rate (called rate control)
• Preventing blood clots (called prevention of thromboembolism such as stroke)
• Managing risk factors for stroke
• Preventing additional heart rhythm problems
• Preventing heart failure