Causes and Risk Factors of Atrial Fibrillation

Atrial fibrillation (AFib) is a fast and very irregular heart rhythm caused by extremely rapid and chaotic electrical impulses originating in the heart's atria (the two upper cardiac chambers). It can develop due to abnormalities of the heart structure that you are born with or after damage to the heart, such as with high blood pressure, coronary artery disease, or a heart attack. But in some people, atrial fibrillation occurs without any heart defects or damage, and it is often seen in people who are older, overweight, and sedentary.

Worldwide, atrial fibrillation is one of the most common arrhythmias that doctors see in their practices.

Atrial fibrillation appears to be related to changes that can occur within the atrial muscle, chiefly inflammation, fibrosis, and increased pressure in the atrial chambers. These changes can disrupt the way atrial tissue handles the electrical impulses of the heart, resulting in AFib.

One condition that produces these disruptive changes in atrial tissue is atrial fibrillation itself. Once atrial fibrillation occurs, it is more likely to come back again—and to get worse as time goes by. Some experts say, “atrial fibrillation begets atrial fibrillation.” This is one reason atrial fibrillation is thought to be a progressive problem, with episodes gradually becoming more frequent and lasting longer as time passes.

Almost any cardiac disease can increase the stress on atrial tissue, producing the kinds of inflammation and fibrosis associated with atrial fibrillation. These can be conditions that develop over time or ones you are born with (such as malformed heart valves).

Damage to your heart due to a heart attack, inflammation of the heart muscle or heart lining, and heart surgery are risk factors for atrial fibrillation. Chronic conditions that damage the heart, especially uncontrolled high blood pressure, raise your risk as well.

The heart problems most likely to be accompanied by atrial fibrillation are:

• Valvular heart disease, especially rheumatic heart disease
• Coronary artery disease
• Heart failure
• Hypertrophic cardiomyopathy
• Congenital heart disease
• Sinus node disease (sick sinus syndrome)
• Other cardiac arrhythmias, especially supraventricular tachycardia (SVT)
• Chronic hypertension
• Cardiac surgery

Several non-cardiac conditions also greatly increase the risk of developing atrial fibrillation. These include:

• Pulmonary embolus
• Pneumonia
• Diabetes
• Sleep apnea
• Chronic kidney disease
• Hyperthyroidism
• Dysautonomia
• High birth weight

While the propensity for atrial fibrillation seems to be higher in some families, the genetic contribution to this arrhythmia is very complex. Still, a history of atrial fibrillation in a close relative significantly increases your risk of developing this arrhythmia. Familial atrial fibrillation may be a factor in up to 30% of cases of idiopathic atrial fibrillation. It may be caused by a single gene mutation or a mix of genes, environmental, or lifestyle risk factors.

KCNQ1 is one gene that has been identified. It is inherited in the autosomal dominant pattern, which means that it affects both men and women equally and that you are likely to display symptoms if you have the gene. Either parent would have atrial fibrillation and any children inheriting the gene are likely to experience atrial fibrillation.

This gene directly affects the ability of the heart muscle cells to bring potassium ions into and out of the cell, as is needed for producing the heart rhythm. Other genes have been found that affect ion channels and can cause atrial fibrillation.

Mutations in genes that affect the development of the heart and muscle cells in the heart before birth are also a genetic cause of atrial fibrillation. These can affect the structure and the function of the heart.

Some inherited gene mutations work in combination with other factors to raise the risk of developing atrial fibrillation. When combined with other conditions such as high blood pressure, diabetes, or atherosclerosis you are at increased risk.

Doctors are just now becoming aware of the extent to which atrial fibrillation is a lifestyle disease. The typical patient a doctor sees with atrial fibrillation likely has no identifiable underlying cause (that is, no structural heart disease, diabetes, sleep apnea, or any of the other conditions listed above). But they are often older, overweight, and sedentary.

It is becoming more and more evident that being overweight and not getting much exercise are strongly associated with atrial fibrillation.

Lifestyle factors that affect your risk of AFib are, to a large extent, within your control:

People whose body mass index (BMI) is greater than 30 kg/m2—that is, those who are classified as being medically obese—have a significantly higher risk of atrial fibrillation than those whose BMI is below 25. Obesity is associated with elevated left atrial pressures, and also with increased pericardial fat (fatty deposits on the pericardium, which is the outside layer of the heart). Both of these factors are thought to contribute to obesity-associated atrial fibrillation.

Sedentary Lifestyle

Several studies have now demonstrated that a very sedentary lifestyle can significantly predispose people to atrial fibrillation. Indeed, at least two studies have shown that, in obese, sedentary people with atrial fibrillation, a strict lifestyle modification program that achieved weight loss and physical conditioning significantly reduced, and sometimes eliminated, the risk of subsequent atrial fibrillation.

These lifestyle-induced improvements in atrial fibrillation are accompanied by measurable improvements in the heart itself—reductions in pericardial fat deposits, and in atrial fibrosis and inflammation.

While moderate drinking does not commonly trigger atrial fibrillation, binge drinking does so fairly often. Most of the time, atrial fibrillation in drinkers follows a night or weekend of heavy drinking, a condition dubbed “holiday heart.”

In at least one prospective study, the concentration of particulate air pollution was associated with a higher risk of atrial fibrillation.

To reduce your risk of cardiovascular disease and, as a result, atrial fibrillation:

• Don’t smoke. Smoking tobacco is probably the most powerful and reliable way to increase your risk of heart disease.
• Keep your weight down.
• Eat a heart-healthy diet. While the “best” diet to prevent heart disease is a point of continuing controversy, most experts now agree that Mediterranean-style diet is good for the cardiovascular system. Foods high in omega-3 fatty acids, such as fish, are excellent choices.
• Get plenty of exercise. A sedentary lifestyle is bad for your health in so many ways. We can now add atrial fibrillation to the list.
• Check your blood pressure regularly. If you develop hypertension, make sure it is adequately treated.
• Make sure your doctor is checking your cholesterol levels and thinking about whether you need to take action to improve them.
• If you drink alcohol, do so only in moderation.

While many doctors regard atrial fibrillation as “just one of those things” that happens to certain people, there are clearly steps you can take to alter that fate. Most of these risk-reduction strategies are the very same things that can reduce your risk of cardiovascular health issues in general. And by preventing coronary artery disease, heart failure, and hypertensive heart disease, you will also be lowering your risk for diabetes, sleep apnea, obesity, pulmonary embolus, and cardiac surgery. Avoiding all these conditions will eliminate some of the most powerful risk factors for atrial fibrillation.