Atrial fibrillation: An old disease, a new epidemic

Atrial fibrillation is a growing epidemic (1–3) with substantial effects on mortality and morbidity in our increasingly elderly population. There are about 2.3 million persons in the United States who have atrial fibrillation (4), a number that is projected to increase to 5.6 million by 2050 (5). The magnitude of this public health problem is closely related to demographic changes; particularly, the relation between age and atrial fibrillation (6). In the United States, the number of persons older than 65 years is estimated to double during this period (7), with those aged 85 years or older comprising the fastest growing segment (8), or 24% of the elderly population (7). In the United States, the societal burden brought about by an increased prevalence of atrial fibrillation is amplified by a convergence of other factors, as expressed in the Framingham Heart Study (9) and the Rochester Epidemiology Project (10). Even after adjustment for age, the prevalence of atrial fibrillation increased significantly during a 22-year period among men in the Framingham study and during a 30-year period among men and women in the Rochester study. In the Framingham Heart Study, secular trends in the rates of heart failure, valvular heart disease, and myocardial infarction could not account entirely for the trends in atrial fibrillation; multiple factors may have been operating simultaneously. Today, not only are more persons reaching the age at which atrial fibrillation is more common, but the elderly are in many ways “sicker” than their counterparts 20 to 30 years ago. A significant number have survived with conditions that may themselves be risk factors or markers for the development of atrial fibrillation, such as hypertension, myocardial infarction, coronary artery bypass surgery, and heart failure. The extent that other noncardiovascular conditions, such as sleep apnea, obesity, postoperative state, lung and thyroid conditions, and alcohol intake, affect the age-adjusted increase in atrial fibrillation is unknown. Although data on the epidemiology of atrial fibrillation have been invaluable in defining the magnitude of the problem, the effects of atrial fibrillation on morbidity and mortality remain poorly understood. In this issue of the Journal, the Marshfield Epidemiologic Study Area (MESA) (11) and the Renfrew/Paisley study (12) provide new and important insights about outcomes related to atrial fibrillation and highlight its effects on the elderly population, confirming that atrial fibrillation is an independent predictor of all-cause mortality (13–15). The two studies present data that atrial fibrillation (as well as atrial flutter in MESA) independently predicts premature death. In MESA, atrial fibrillation in patients with a first diagnosis of atrial arrhythmia was associated with a threefold increase in the risk of death over a mean ( SD) follow-up of 3.6 2.3 years, after adjusting for baseline cardiovascular risk factors, compared with ageand sex-matched controls. However, because the cause of death was not reported, whether atrial fibrillation treatment, noncardiovascular conditions, or both, might have affected mortality could not be determined. The 6-month mortality of these patients was 17%, suggesting that a substantial proportion of patients who developed atrial fibrillation was very ill, and that atrial fibrillation was a marker of terminal illness. Patients with atrial flutter also had a more favorable mortality risk initially compared with those with atrial fibrillation, although mortality became similar in the two groups in the long term. Similarly, in the Renfrew/Paisley study atrial fibrillation was associated with a 2.2-fold excess risk of death among women and a 1.5-fold increase in risk among men during a 20-year period. Both heart failure and stroke contributed to this excess mortality in these patients. It is unclear whether the association between atrial fibrillation and mortality is a direct causal relation or whether atrial fibrillation is a marker of other comorbid conditions. “Lone” atrial fibrillation, which includes patients without structural heart disease, does not appear to have an adverse effect on survival. Therefore, it is conceivable that the interaction of atrial fibrillation with underlying structural heart disease provides the substrate for increased mortality. The mechanisms whereby atrial fibrillation could increase mortality are not understood completely, but the altered hemodynamic milieu following the development of atrial fibrillation, with a rapid and irregular ventricular rate in patients with underlying cardiovascular disease, may contribute to or further augAm J Med. 2002;113:000. Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic Rochester, Minnesota. Requests for reprints should be addressed to Bernard J. Gersh, MB, ChB, DPhil, at Mayo Clinic, 200 First Street SW,Rochester, Minnesota 55905 , or Gersh.Bernard@mayo.edu. Manuscript submitted February 11, 2002.