The Beat Goes On
What You Need to Know About Atrial Fibrillation
By Gregory A. Cogert, MD, FACC, FHRS
WHAT IS ATRIAL FIBRILLATION?
Atrial fibrillation (AF) is the most common heart rhythm problem in America, with over 4 million people who carry the diagnosis of AF and many more yet to be diagnosed. So, just what is AF?
Normally, every beat of the heart is initiated by the upper chamber (atrium) contracting. This atrial impulse facilitates the flow of blood to the ventricle, which in turn pumps blood to the body. In addition to keeping the blood flowing normally, the atrium sets the heart rate, going faster during periods of stress or exercise and slower during rest. With atrial fibrillation, there is continuous chaotic electrical activity in the atrium with no atrial contraction and no atrial control of the heart rate. The loss of normal atrial blood flow can result in clotting of blood in the heart. The loss of heart rate control results in an erratic heart rate that can often be dangerously fast or slow.
Atrial fibrillation can result in a dramatic reduction in quality of life, physical condition, mental health, social functioning as well as cause congestive heart failure, stroke, dementia, and death.
WHO IS AT RISK FOR ATRIAL FIBRILLATION?
There is an increasing incidence with age and it is estimated that 25% of adults over 40 will develop AF during their lifetime. The most common risk factors for AF are age, high blood pressure, obesity, and obstructive sleep apnea. Patients with any chronic medical problem are at an increased risk for AF, especially problems of the heart, lungs, kidney, thyroid and diabetes.
HOW IS ATRIAL FIBRILLATION TREATED?
Preventing Stroke
The first step in the treatment of AF is to evaluate the risk of stroke and initiate a treatment plan to minimize that risk. There are 5 classic risk factors for stroke in AF. They are the “CHADS risk factors”
C = Congestive Heart Failure
H= Hypertension
A= Age over 75 years old
D= Diabetes
S= prior Stroke or TIA
The risk for stroke in AF with none of these risk factors is under 2% whereas in the presence of all 5 the annual stroke rate approaches 20%. Stroke risk is also increased in women, patients over 65 years old, and the presence of vascular disease.
There are currently three approved anticoagulant medications (blood thinners) used to minimize stroke in AF.
Warfarin: Blocks the liver’s production of clotting factors. Warfarin was the only option prior to 2010. Warfarin is a once daily medication that is affordable. An individual’s dose is highly variable and frequent blood tests are required to confirm the correct dosing. Negatives include multiple food and drug interactions resulting in frequent dose changes and blood tests.
Dabigatran: Direct Thrombin Inhibitor. Approved by the FDA October 2010. In a large research trial was found to be superior to warfarin. If kidney function is stable, the dosing is reliable and no blood tests are required. There are significantly less food and drug interactions than warfarin. It is more expensive and there are less long term safety data than warfarin. Negatives include the cost, twice daily dosing, and 10% of patients do not tolerate due to stomach irritation.
Rivaroxaban: Clotting factor (Xa) inhibitor. Approved for treatment of AF November 2011. Similar to dabigatran with stable dosing and minimal food and drug interactions negating the need for frequent blood tests in patients with stable kidney function. Cost is similar to dabigatran. In the large research trial that led to approval, its effectiveness was found to be equivalent to warfarin (as opposed to superiority seen with dabigatran). Advantages include once daily dosing and an improved side effect profile.
Treating the Symptoms
There are two strategies to minimize symptoms of AF: the “rate control” and “rhythm control” strategies. The goal of the rate strategy is to keep the heart rate within a normal range while permitting the atria to remain in fibrillation. The goal of the rhythm strategy is to maintain normal atrial function.
The advantage of the rate control strategy is the ease with which it is employed. If the heart is too fast, slowing medications are given. If the heart is too slow, a pacemaker is inserted to speed it up. If the medications are not effective or not tolerated, a simple ablation of the heart’s electrical connection from the atrium to ventricle (AV node) is performed making the heart dependent on the pacemaker to beat.
The main disadvantage to the rate control strategy is the commitment to AF. Often symptoms continue despite rate control due to the absence of atrial contraction and the loss of a physiologic heart rate control. This strategy is generally pursued in elderly, sedentary patients with a long history of atrial fibrillation and minimal symptoms.
The advantage of the rhythm strategy is that, when successful, it restores normal heart function. Rhythm control is obtained by medications, catheter ablation, or heart surgery. In its early stages, AF tends to be intermittent (paroxysmal). If it progresses to become persistent, an electrical shock (cardioversion) is often required to regain normal rhythm. The longer a patient remains in AF, the greater likelihood they will become permanently in AF.
Catheter ablation involves electrically isolating the pulmonary veins in the left atrium that trigger AF. Prompted by research trials of over 7000 patients undergoing ablation showing superiority to medication, the Heart Rhythm Society, American College of Cardiology, and American Heart Association published the 2011 AF guidelines giving ablation a class I recommendation for the first line treatment of many patients with AF1. Through 2011, the Oklahoma Heart Institute physicians have performed over 350 AF ablations. Although research data is mounting that ablation can reduce the risk of stroke, congestive heart failure, and dementia, ablation is currently restricted to patients with symptomatic AF pending validation of this data.
The main disadvantage of the rhythm control strategy is the time and expense required to eliminate AF. The single procedure success rate without medication is 70%. Often additive medications or additional procedures are required to maintain normal rhythm.
SUMMARY
Atrial Fibrillation is the most common heart rhythm problem in America. It can decrease quality of life and cause congestive heart failure, stroke, dementia, and death. Risk factors for AF include older age, hypertension, and obesity. The first step in management is to minimize stroke risk. The second step is to minimize symptoms. Ablation of AF is superior to medical therapy and recently received a class 1 recommended for the first line treatment of AF.
REFERENCES
1. 2011 ACCF/AHA/HRS focused update on the management of patients with atrial fibrillation, Heart Rhythm 2011;8(1): 157-76