Prevalence and Incidence of Atrial Fibrillation
Determination of the prevalence of atrial fibrillation (AF) in a given population depends on cohort selection and the methods used for the identification and validation of AF. The US Census Bureau states that in 2010, the population of the United States was 309 million people, and 5.2 million of them were estimated to have AF. This suggests a prevalence of AF in the general population of 1.7%. By 2020, the population of the United States had increased to 329.5 million. At a prevalence of 1.7%, this would suggest that in 2020, approximately 5.6 million people in the United States had AF. In 2020, the global population was 7.8 billion people, and 50 million were estimated to have AF ( Fig. 2.1 ). This suggests a prevalence of AF in the world’s population of 0.6%. These ranges of data are consistent with historical estimates and provide a basis for the general “rule of thumb” that at least 1% of any general population can be expected to have AF.
Age-standardized global prevalence of AF and atrial flutter per 100,000 distributed by country.
(Source: Institute for Health Metrics and Evaluation. Used with permission. All rights reserved)
In 2010, the incidence of newly diagnosed AF was estimated to be 1.2 million per year in the United States. The lifetime risks of AF are 1 in 3 among Whites, 1 in 5 among Blacks, and 1 in 7 among Asians. , Asian males had a higher lifetime risk of AF than Asian females (16.9% versus 14.6%, respectively), but a European study showed that differences in AF incidence observed by sex may be explained by a sex-specific distribution of risk factors. The incidence of AF has remained relatively stable over time, contributing to a tripling of AF prevalence over the past 50 years. Projections for the next 50 years indicate that AF prevalence will double in the United States by 2050, with nearly 16 million US citizens having AF ( Fig. 2.2 ). , It is also predicted that by 2060, nearly 18 million people in the European Union will have AF ( Fig. 2.3 ). ,
Projected number of people in the United States with atrial fibrillation (AF). It will reach nearly 16 million by 2050.
(Reproduced from Go AS, Hylek EM, Phillips KA, et al. Prevalence of diagnosed atrial fibrillation in adults: national implications for rhythm management and stroke prevention: the Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) study. J Am Med Assoc. 2001;285(18):2370–2375 and Miyasaka Y, Barnes ME, Gersh BJ, et al. Secular trends in incidence of atrial fibrillation in Olmsted County, Minnesota, 1980 to 2000, and implications on the projections for future prevalence. Circulation. 2006;114(2):119–125.)
Projected number of people in the European Union with atrial fibrillation (AF). It will reach nearly 18 million by 2060. (A) The Di Carlo and coworkers prediction for patients in three different age groups. (B) The Krijthe and coworkers prediction for patients younger and older than 75 years of age and for men and women.
(Modified from Krijthe BP, Kunst A, Benjamin EJ, et al. Projections on the number of individuals with atrial fibrillation in the European Union, from 2000 to 2060. Eur Heart J. 2013;34(35):2746–2751 and Di Carlo A, Bellino L, Domenico C, et al. Prevalence of atrial fibrillation in the Italian elderly population and projections from 2020 to 2060 for Italy and the European Union: the FAI project. Europace. 2019;21(10):1468–1475.)
The onset of AF can be accompanied by the sensation of palpitations, diaphoresis, shortness of breath, dyspnea on exertion, fatigue, malaise, worsening heart failure, or exacerbation of angina pectoris. Although these symptoms range from being only troublesome in some patients to being debilitating in others, AF can also be asymptomatic, leaving patients completely unaware that they have AF even over a period of years. In cardiac surgery patients, the cause of AF is usually left-heart disease, including mitral valve, aortic valve, and/or coronary artery disease, as well as systemic hypertension and/or left ventricular (LV) failure. However, in asymptomatic patients without structural heart disease, both the presence of AF and its cause are often unknown (“cryptogenic AF”). AF is the most common arrhythmia encountered in clinical medicine. It is also the most common arrhythmia encountered by cardiac surgeons because many patients who require surgery also have AF (see Chapter 23 ), and roughly 35% of all patients undergoing cardiac surgery develop postoperative AF (see Chapter 47 ).
Impact of Atrial Fibrillation on Survival
AF is second only to ventricular fibrillation in its lethality. Piccini and colleagues examined rates and risk factors for clinical events after new-onset AF in 230,940 hospitalized Medicare patients. AF increased the incidence of death, heart failure, myocardial infarction, stroke, and gastrointestinal bleeding, with the cumulative risk of death approaching 50% at 5 years ( Fig. 2.4 ). By tabulating the available statistics from the National Cancer Institute with Piccini and colleagues’ study of more than 230,000 Medicare patients, it is possible to compare the 5-year survival rate after new-onset AF with the 25 most common cancers in the United States. Such a comparison shows that AF places number 11 on the list ( Fig. 2.5 ). Most hospitalized Medicare-age men would likely prefer a diagnosis of AF rather than melanoma, but their 5-year survival rate is better with melanoma than with new-onset AF. Likewise, most hospitalized Medicare-age women would probably prefer to be told that they have new-onset AF than that they have breast cancer, but their likelihood of being alive in 5 years is substantially better if they have newly diagnosed breast cancer than if they have newly diagnosed AF.
Cumulative incidence of events in the 5 years after diagnosis of in-hospital atrial fibrillation (AF) in Medicare patients. GI, Gastrointestinal; MI, myocardial infarction.
(Reproduced from Piccini JP, Hammill BG, Sinner MF, et al. Clinical course of atrial fibrillation in older adults: the importance of cardiovascular events beyond stroke. Eur Heart J. 2014;35(4):250–256.)
Five-year survival rates for the top 25 cancers in the United States compared with the 5-year survival rate for new-onset atrial fibrillation in Medicare patients. CNS, Central nervous system.
(Adapted from Piccini JP, Hammill BG, Sinner MF, et al. Clinical course of atrial fibrillation in older adults: the importance of cardiovascular events beyond stroke. Eur Heart J. 2014;35(4):250–256 and National Cancer Institute. 2013. https://seer.cancer.gov/statfacts/html/common.html ).
AF has a significantly worse impact on survival in women than in men. In the Renfrew/Paisley Study from Scotland, 7052 men and 8354 women (age 45–64 years) with and without AF were followed for 20 years. In patients without AF, the survival rate in women was roughly 20% higher than in men ( Fig. 2.6 ). AF caused a survival decrease of 25% in men and a 45% decrease in women. The worse impact of AF in women resulted in their having essentially the same 20-year survival rate as men, indicating that AF in women is far more lethal than it is in men.
Atrial fibrillation (AF) decreases the survival rate in women far greater than it does in men. Without AF, women have a higher life expectancy. However, the survival rate is the same in men and women who AF.
(Reproduced from Stewart S, Hart MA, Hole DJ, McMurray JJV. A population-based study of the long-term risks associated with atrial fibrillation: 20-year follow-up of the Renfrew/Paisley study. Am J Med. 2002;113:359–364.)
Impact of Atrial Fibrillation on Stroke
The 1991 Framingham Study of 5070 patients followed for 34 years documented that patients with AF were five times more likely to have a stroke than patients without AF. Approximately 90% of all strokes are ischemic, and the other 10% are hemorrhagic ( Fig. 2.7 ). Hemorrhagic strokes are more lethal than ischemic strokes. Patients with AF can have ischemic strokes because of systemic thromboembolism or hemorrhagic strokes caused by overanticoagulation. Approximately 25% of thromboembolic strokes are associated with AF. Globally, the number of ischemic strokes was 7.86 million in 2020, so the number of ischemic strokes caused by AF globally was approximately 2 million. Of the 800,000 annual strokes in the United States, 90% are ischemic, and 180,000 are associated with AF. Europeans have approximately 1.12 million strokes per year, 90% of which are ischemic, meaning that approximately 250,000 strokes occur annually in association with AF. The cause of ischemic strokes associated with AF is systemic thromboembolism, usually originating from the left atrial appendage (LAA; see Section V). The ability to treat patients with AF successfully and to close the LAA by catheter and surgical techniques raises the possibility that the frequency of stroke in patients with AF might be decreased in the future.
Approximately 90% of all strokes are ischemic, and 10% are hemorrhagic. Atrial fibrillation (AF) is associated with approximately 25% of all ischemic strokes. This means that AF is associated with roughly 2 million strokes per year globally, 180,000 per year in the United States, and 250,000 per year in Europe.
Atrial Fibrillation and Heart Failure
New-onset AF in hospitalized Medicare patients results in the development of heart failure in approximately 13% of patients within 5 years (see Fig. 2.4 ). However, not only can AF cause heart failure, but heart failure can also cause AF. A recent Mayo Clinic review of this relationship stated, “Atrial fibrillation (AF) is the most common arrhythmia among patients with heart failure (HF), and HF is the most common cause of death for patients presenting with clinical AF.” There are two major types of clinical heart failure: heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF).
Sustained AF with a rapid ventricular response can cause HFrEF because of tachycardia-induced ventricular cardiomyopathy. Elimination of AF in these patients by catheter or surgical ablation commonly results in a return of the left ventricular ejection fraction (LVEF) toward normal and amelioration of the heart failure. However, most patients with HFrEF develop secondary AF because of a chronically low LVEF, and the elimination of AF may have little salutary effect on the heart failure. Thus, in patients who present with simultaneous AF and HFrEF, it is often challenging to determine if the AF has caused tachycardia-induced HF or if a primary LV cardiomyopathy has caused the AF. The relationship between AF and HF in this clinical situation is a bit like the conundrum of “Which came first, the chicken or the egg?” The distinction is critical because it determines whether or not AF ablation will be beneficial to the patient.
The pathogenesis of AF in patients with HFpEF is distinctly different from that in patients with HFrEF. AF in patients with HFpEF is thought to be caused by systemic inflammation resulting in abnormal myocardial remodeling and functional reserve. This results in LV diastolic dysfunction while leaving LV systolic function intact. The left atrium often enlarges in response to this abnormal LV physiology, leading to AF. Development of secondary AF in HFpEF patients can have a profoundly negative effect on the severity of clinical heart failure, and the risk of progression of paroxysmal AF to persistent AF is dramatic ( Fig. 2.8 ). Drug-refractory AF in patients with HFpEF may require catheter ablation, but if surgery for AF is required in these patients, one should be careful about occluding the LAA if the LV diastolic dysfunction is severe (see Chapter 40 ).
