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Prevalence of atrial fibrillation in the general population of Japan: An analysis based on periodic health examination

      Abstract

      Background

      The mortality and morbidity rates of various cardiovascular diseases differ between Western countries and Japan. The age- and gender-specific prevalence rate of atrial fibrillation (AF) in the general population of Japan was determined using the data from periodic health examinations in 2003.

      Methods

      Data of 630,138 subjects aged 40 years or more (47% were men and 34% were employees of companies and local governments) were collected from northern to southern Japan. The prevalence of diagnosed AF in each 10-year age group of both men and women was determined. Based on these prevalence rates and the Registry of Residents, the number of people having AF in Japan was estimated.

      Results

      The prevalence rate of AF increased as both male and female subjects aged, and it was 4.4% for men but only 2.2% for women aged 80 years or more (p<0.0001). As a whole, the AF prevalence of men was three times that of women (1.35 versus 0.43%, p<0.0001). There may be approximately 716,000 people (95% confidence interval (CI), 711,000–720,000) with AF in Japan, an overall prevalence of 0.56%. The number of people having AF was projected to be 1.034 (95% CI, 1.029–1.039) million, an overall prevalence of 1.09%, in 2050.

      Conclusions

      The prevalence of AF increased in Japan as the population aged, as in Western countries. The overall prevalence of AF in Japan is approximately two-thirds of that in the USA. The projected increase in the number of people having AF is modest in Japan in 2050.

      Keywords

      1. Introduction

      Atrial fibrillation (AF) is one of the common arrhythmias encountered in general practice as well as in the field of cardiology. AF could be responsible for increased mortality and various morbidities including clinical symptoms, impaired cardiac function and thromboembolism [
      • Kannel W.B.
      • Wolf P.A.
      • Benjamin E.J.
      • Levy D.
      Prevalence, incidence, prognosis, and predisposing conditions for atrial fibrillation: population-based estimates.
      ,
      • Kannel W.B.
      • Abbott R.D.
      • Savage D.D.
      • McNamara P.M.
      Epidemiologic features of chronic atrial fibrillation: the Framingham Study.
      ,
      • Krahn A.D.
      • Manfreda J.
      • Tate R.B.
      • Mathewson F.A.L.
      • Cuddy T.E.
      The natural history of atrial fibrillation: incidence, risk factors, and prognosis in the Manitoba follow-up study.
      ,
      • Dries D.L.
      • Exner D.V.
      • Gersh B.J.
      • Domanski M.J.
      • Waclawiw M.A.
      • Stevenson L.W.
      Atrial fibrillation is associated with an increased risk for mortality and heart failure progression in patients with asymptomatic and symptomatic left ventricular systolic dysfunction: a retrospective analysis of the SOLVD trials.
      ,
      • Vidaillet H.
      • Granada J.F.
      • Chyou P.H.
      • et al.
      A population-based study of mortality among patients with atrial fibrillation or flutter.
      ]. Several epidemiological studies from Western countries showed that prevalence of AF increased with the aging of the population and that the increase became striking after 60 years of age, affecting approximately 8% to 9% of people aged 80 years or more [
      • Wolf P.A.
      • Abbott R.D.
      • Kannel W.B.
      Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.
      ,
      • Furberg C.D.
      • Psaty B.M.
      • Manolio T.A.
      • Gardin J.M.
      • Smith V.E.
      Rautaharju PM for the CHS Collaborator Research Group
      Prevalence of atrial fibrillation in elderly subjects (the Cardiovascular Health Study).
      ,
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ,
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ,
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      ].
      Several predisposing factors for AF other than aging are known [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ,
      • Djousse L.
      • Levy D.
      • Benjamin E.J.
      • et al.
      Long-term alcohol consumption and the risk of atrial fibrillation in the Framingham study.
      ]. Among them are hypertension, myocardial infarction, valvular heart disease, congestive heart failure, diabetes mellitus, alcohol drinking and others [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ,
      • Djousse L.
      • Levy D.
      • Benjamin E.J.
      • et al.
      Long-term alcohol consumption and the risk of atrial fibrillation in the Framingham study.
      ]. The prevalence, mortality and morbidity of various cardiovascular diseases may differ between Western countries and Japan. For example, prevalence of hypertension of Japan seems higher than that of the USA, but lower than that of England and Germany [
      • Kubo M.
      • Kiyohara Y.
      • Kato I.
      • et al.
      Trends in the incidence, mortality, and survival rate of cardiovascular disease in a Japanese community. The Hisayama Study.
      ,
      • Miyamatsu N.
      • et al.
      for the NIPPON DATA80 Research Group
      Different effects of blood pressure on mortality from stroke subtypes depending on BMI levels: a 19-year cohort study in the Japanese general population — NIPPON DATA80.
      ,
      • Wolf-Maier K.
      • Cooper R.S.
      • Banegas J.R.
      • et al.
      Hypertension prevalence and blood pressure levels in 6 European countries, Canada, and the United States.
      ,
      • Hajjar I.
      • Kotchen T.A.
      Trends in prevalence, awareness, treatment, and control of hypertension in the United States, 1988–2000.
      ]. Another example is coronary artery disease. The incidence of myocardial infarction is lower and the prognosis after myocardial infarction is better in Japan than in Western countries [
      • Sekikawa A.
      • Satoh T.
      • Hayakawa T.
      • Ueshima H.
      • Kuller L.H.
      Coronary heart disease mortality among men aged 35–44 years by prefecture in Japan in 1995–1999 compared with that among white men aged 35–44 by State in the United States in 1995–1998. Vital statistics data in recent birth cohorts.
      ,
      • Yokoyama M.
      • et al.
      for the Japan EPA Lipid Intervention Study Investigators
      Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis.
      ,
      GISSI-Prevenzione Investigators (Gruppe Italiano per lo Studio della Sopravvienza nell'infarto miocardico)
      Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial.
      ]. Therefore, it seems conceivable that the epidemiology of AF could differ between Western countries and Japan. However, the epidemiological study of AF has been limited in Japan [
      • Nakayama T.
      • Date C.
      • Yokoyama T.
      • Yoshiike N.
      • Yamaguchi M.
      • Tanaka H.
      A 15.5-year follow-up study of stroke in a Japanese provincial city. The Shibata Study.
      ,
      • Kitamura A.
      • Shimamoto T.
      • Doi M.
      • et al.
      Secular trends in prevalence and incidence of atrial fibrillation and associated factors in a Japanese rural population.
      ,
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      ]; these epidemiological studies [
      • Nakayama T.
      • Date C.
      • Yokoyama T.
      • Yoshiike N.
      • Yamaguchi M.
      • Tanaka H.
      A 15.5-year follow-up study of stroke in a Japanese provincial city. The Shibata Study.
      ,
      • Kitamura A.
      • Shimamoto T.
      • Doi M.
      • et al.
      Secular trends in prevalence and incidence of atrial fibrillation and associated factors in a Japanese rural population.
      ,
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      ] showed the prevalence of AF was lower in Japan than in Western countries [
      • Wolf P.A.
      • Abbott R.D.
      • Kannel W.B.
      Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.
      ,
      • Furberg C.D.
      • Psaty B.M.
      • Manolio T.A.
      • Gardin J.M.
      • Smith V.E.
      Rautaharju PM for the CHS Collaborator Research Group
      Prevalence of atrial fibrillation in elderly subjects (the Cardiovascular Health Study).
      ,
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ,
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ,
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      ].
      Japan has a periodic health examination system for company employees and community residents that cover the country. The Industrial Safety and Health Law decrees provision of a health examination that includes an electrocardiogram for examinees aged 40 years or more. In order to determine the prevalence of AF in the general population of Japan, we conducted a cooperative epidemiological study using the data from periodic health examinations of more than 600,000 subjects over the age of 40 years.

      2. Subjects and methods

      Data from periodic health examinations of community residents and employees of companies and local governments performed in 2003 were collected. After obtaining approval of the study design from the ethics committee of the participating institutes, which are distributed from the northern part of the main island of Honshu to Kyushu island of Japan, the health examination data were collected from company clinics, health screening centers, and local governments of the prefectures where the participating institutes are located.
      Employees of companies and local governments undergo an annual health examination provided by their companies and governments; other people undergo a health examination provided by the local governments of their communities. Most employees of companies and governments retire at 60 years of age, and after retirement they undergo the annual health examination provided by their local governments. Health examination includes measurement of blood pressure, electrocardiogram, chest X-ray, urinalysis, and testing for blood cell count and blood chemistry. AF was diagnosed electrocardiographically by a trained doctor in each of participating centers and clinics. Conventional diagnostic criteria of AF, i.e., a grossly irregular ventricular rhythm of supraventricular origin, no visible P wave and irregular fluctuation of the baseline, were employed. In the present study, subjects were defined as having AF when their electrocardiogram showed AF at the time of health examination. Therefore, those with a history of paroxysmal AF but not having an AF episode at the time of the health examination were not counted as having AF in the following analyses.
      Because the number of examinees exceeded 600,000, we collected the prevalence of AF of each 10-year age group for both men and women to calculate gender- and age-specific prevalence rates of AF. Then we estimated the absolute number of people with AF in each 10-year age group using the Japanese Registry of Residents in 2005 [
      Japanese Registry of Residents in 2005. The Ministry of Internal Affairs and Communications, Japan. Statistics Bureau.
      ], and projected the absolute number of people having AF in the years of 2010–2050 using the medium variant estimation of the Population Projection for Japan [
      Population Projection for Japan. National Institute of Population and Social Security Research, Japan.
      ].
      Conventional diagnostic criteria of hypertension, hypercholesterolemia, and diabetes mellitus were employed in our health examination system. Hypertension was defined as a systolic blood pressure of 140 mmHg or higher, a diastolic blood pressure of 90 mmHg or higher, or both (Japanese Society of Hypertension, 2000). Hypercholesterolemia was defined as a total cholesterol level of 240 mg/dl or higher (Japanese Atherosclerosis Society, 2002), and diabetes mellitus, as a random blood glucose concentration of 200 mg/dl or a fasting blood glucose concentration of 126 mg/dl (Japan Diabetes Society, 1999). Additionally, in the present study, subjects were defined as having any comorbidity if they had been given drugs for hypertension, hypercholesterolemia, diabetes mellitus, or cardiac diseases. Gender-specific prevalence of comorbidity was determined for subjects with and without AF.

      2.1 Statistical analyses

      Because of the number of subjects exceeding 600,000 and simplicity of data analyses, age- and gender-specific prevalence rates of AF and gender-specific prevalence of clinical characteristics were determined and compared with chi-square test. Independent predictors of AF were not determined in the present study. A p value less than 0.05 was considered statistically significant.

      3. Results

      Data of 630,138 subjects aged 40 years or more were collected from 25 company clinics, nine health screening centers of communities, and five local governments. Approximately 47% of the subjects were male; 31% of the subjects were aged 50–59 years, 27% were aged 40–49 years, and 23% were aged 60–69 years. Employees of companies and local governments accounted for 34% of all subjects of the study group.

      3.1 Age- and gender-specific prevalence rate of AF

      Since the age- and gender-specific AF prevalence of company employees and community residents was very similar, the data of both groups were pooled as a single group for the following analyses. In Table 1, age- and gender-specific prevalence rates of AF are summarized. AF prevalence increased as the subjects aged in both men and women (p<0.0001), and was lower in women than in men for each age group (p<0.0001). It was 4.4% for men aged 80 years or more, but was only 2.2% for women of the same age; as a whole, the AF prevalence of men was three times as great as that of women (1.35 versus 0.43%, p<0.0001).
      Table 1Age- and gender-specific number of examinees and subjects with AF.
      Number of examineesNumber of subjects with AF
      MenWomenMenWomen
      Age (years)
      40–4988,15680,432211 (0.24%)30 (0.04%)
      50–5996,90197,070760 (0.78%)112 (0.12%)
      60–6957,99886,1561,126 (1.94%)360 (0.42%)
      70–7941,77058,2961,436 (3.44%)653 (1.12%)
      80–10,42712,932462 (4.43%)283 (2.19%)
      All ages295,252334,8863,995 (1.35%)1,438 (0.43%)
      AF = atrial fibrillation.

      3.2 Clinical characteristics of subjects with AF

      Prevalences of clinical characteristics that could be possible risk factors for AF [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ] are summarized in Table 2. Hypertension, diabetes mellitus, and cardiac diseases were present more frequently in both men and women with AF as compared with those without AF. Alcohol drinking was seen more frequently in men with AF than in those without AF. Hypercholesterolemia and current smoking were not associated with development of AF.
      Table 2Clinical characteristics of subjects with and without atrial fibrillation.
      MenWomen
      AF (+)AF (−)AF (+)AF (−)
      Hypertension (%)42.424.2*38.119.8*
      Diabetes mellitus (%)19.912.6*10.45.0**
      Hypercholesterolemia (%)24.127.615.224.2**
      Cardiac diseases (%)59.14.6*54.84.4*
      Current smoker (%)27.243.5*2.15.2
      Current drinker (%)76.570.5**15.122.6
      AF = atrial fibrillation. *p<0.00001, **p<0.05 versus AF (+).
      A complete set of data was available from 60,038 men and 45,297 women.

      3.3 Estimated number of people with AF

      There may be 716,000 [95% confidence interval (CI), 711,000–720,000] people having AF in Japan, an overall prevalence of 0.56%. As a whole, the absolute number of people with AF peaked at the age of 70–79 years. This was true for men. For women, however, the absolute number of people with AF was the greatest at the age of 80 or more. Eighty-five percent of the people with AF were older than 60 years, and 25% were older than 80 years.
      The absolute numbers of people having AF projected into the future based on the medium variant estimates of the Population Projection for Japan [
      Population Projection for Japan. National Institute of Population and Social Security Research, Japan.
      ] are summarized in Table 3. It would be 1.034 (95% CI, 1.029–1.039) million in the year of 2050, an overall prevalence of 1.09%.
      Table 3Estimated number and prevalence of people with AF.
      YearTotal populationPeople having AFOverall prevalence (%)
      (95% CI)
      (Millions)(Thousands)
      2005
      The population numbers are based on the Japanese Registry of Residents of 2005 (23). Future population numbers were projected using the medium variant estimates of the Population Projection for Japan of the National Institute of Population and Social Security Research (24).
      126.87716 (711–720)0.56
      2010127.18830 (824–835)0.65
      2020122.74974 (969–979)0.79
      2030115.221049 (1044–1055)0.91
      2040105.691051 (1045–1056)0.99
      205095.181034 (1029–1039)1.09
      AF = atrial fibrillation.
      a The population numbers are based on the Japanese Registry of Residents of 2005 (23). Future population numbers were projected using the medium variant estimates of the Population Projection for Japan of the National Institute of Population and Social Security Research (24).

      4. Discussion

      4.1 Major findings

      The major findings of the present study were as follows. First, the prevalence rate of AF increased as people aged, and was three times greater in men than in women. Second, the estimated number of people with AF was approximately 720,000 in Japan, and the overall prevalence was 0.56%, which is two-thirds of that of the USA [
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ]. The number of people having AF in Japan is projected to be 1.034 million in the year of 2050, which is one fifth of that in the USA [
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ].

      4.2 Comparison with data of previous studies

      In Japan, epidemiological studies on AF have been limited in number. Nakayama et al. reported the prevalence of AF as 1.35% among 2305 residents of a community whose age was 40 years or more [
      • Nakayama T.
      • Date C.
      • Yokoyama T.
      • Yoshiike N.
      • Yamaguchi M.
      • Tanaka H.
      A 15.5-year follow-up study of stroke in a Japanese provincial city. The Shibata Study.
      ]. Other investigators [
      • Kitamura A.
      • Shimamoto T.
      • Doi M.
      • et al.
      Secular trends in prevalence and incidence of atrial fibrillation and associated factors in a Japanese rural population.
      ,
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      ] reported the AF prevalence was two to three times greater in men than in women; it was 3% for men and 1.1% for women aged 60–69 years [
      • Kitamura A.
      • Shimamoto T.
      • Doi M.
      • et al.
      Secular trends in prevalence and incidence of atrial fibrillation and associated factors in a Japanese rural population.
      ]. Epidemiological studies on the prevalence of AF in other Asian countries are still limited in number. Lok and Lau [
      • Lok N.S.
      • Lau C.P.
      Prevalence of palpitations, cardiac arrhythmias and their associated risk factors in ambulant elderly.
      ] reported that the prevalence of AF was only 1.3% of ambulatory elderly people aged 60–94 years in Hong Kong.
      In Table 4, representative data of AF prevalence from Western countries and Japan are summarized. They clearly showed that the prevalence of AF increases as a population ages. In the Framingham Study reported by Wolf et al. [
      • Wolf P.A.
      • Abbott R.D.
      • Kannel W.B.
      Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.
      ], the prevalence was 0.1% for people aged 40–49 years, and increased to 8.8% for people aged 80 years or more. By contrast, based on a general practice research database in England and Wales, Majeed et al. [
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      ] showed that prevalence of AF was more than 10% in both men and women aged 85 years or more. The prevalence of AF in the study of Ohsawa [
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      ] as well as in the present study was much lower than the representative data reported from the Western countries [
      • Wolf P.A.
      • Abbott R.D.
      • Kannel W.B.
      Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.
      ,
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ,
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      ].
      Table 4Age-specific prevalence of atrial fibrillation in epidemiological surveys expressed as a percent.
      Wolf et al.
      • Wolf P.A.
      • Abbott R.D.
      • Kannel W.B.
      Atrial fibrillation as an independent risk factor for stroke: the Framingham Study.
      Majeed et al.
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      Go et al.
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      Ohsawa et al.
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      Present study
      Age (years)N=5070N=1.4 millionN=1.89 millionN=23,713N=630,138
      AllMWMWMWMW
      40–440.10.30.20.30.10.20.04
      45–490.10.70.40.30.10.20.04
      50–540.50.70.40.70.40.80.1
      55–590.51.81.10.90.40.70.40.80.1
      60–641.81.81.11.71.01.30.91.90.4
      65–691.84.63.33.01.71.30.91.90.4
      70–744.84.63.35.03.43.82.23.41.1
      75–794.89.17.27.35.03.82.23.41.1
      808.810.610.910.68.03.82.24.42.2
      Age groups were in steps of 10 years starting from 40 years in the studies of Wolf et al., and Ohsawa et al., and in the present study, and starting from 35 years in the study of Majeed et al and were in steps of 5 years from 55 years in the study of Go et al.
      M = men, W = women, and prevalence of atrial fibrillation in subjects aged 85 years or more and in subjects aged 70 years or more, respectively.
      Based on the data of the population-based survey, there are 2.23 million people in the USA having AF [
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ]. It would be 650,000 in England and Wales, an overall prevalence of 1.25% [
      • Majeed A.
      • Moser K.
      • Carroll K.
      Trends in the prevalence and management of atrial fibrillation in general practice in England and Wales, 1994–1998: analysis of data from the general practice research database.
      ]. The present study estimated the number of people having AF to be 720,000 in Japan which was much lower than that reported for the USA [
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ].
      The number of people having AF is expected to increase to 5 million in the USA in the year 2050 [
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ]. Other investigators estimated it to be 12–16 million in the USA by 2050 [
      • Miyasaka Y.
      • Barnes M.E.
      • Gersh B.J.
      • et al.
      Secular trends in incidence of atrial fibrillation in Olmsted County, Minnesota, 1980 to 2000, and implications on the projections for future prevalence..
      ]. By contrast, Ohsawa et al. estimated it to be 1.08 million in Japan in 2030 [
      • Ohsawa M.
      • Okayama A.
      • Sakata K.
      • et al.
      Rapid increase in estimated number of persons with atrial fibrillation in Japan: an analysis from national surveys on cardiovascular diseases in 1980,1990 and 2000.
      ]. Based on the present data, it would be 1.03 million in 2050, a relative increase of 40%. This modest increase in the future number of people with AF could be due to a decrease in number of people aged 50–69 in Japan, although number of people aged 80 years or more would be doubled in 2050 [
      Population Projection for Japan. National Institute of Population and Social Security Research, Japan.
      ].

      4.3 Clinical characteristics of subjects with AF

      Hypertension is a well-known risk factor for AF [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ,
      • Hurley V.
      • Ireson R.
      • Fletcher K.
      • Lip G.Y.P.
      • Hobbs F.D.R.
      Mant J on behalf of the BAFTA Investigators
      A cross-sectional study of hypertension in an elderly population (75 years and over) with atrial fibrillation: secondary analysis of data from the Birmingham Atrial Fibrillation in the Aged (BAFTA) randomised controlled trial.
      ]. Ohsawa et al. clearly showed that hypertension was complicated more frequently with both men and women having AF [
      • Ohsawa M.
      • et al.
      for the NIPPON DATA80 Research Group
      Mortality risk attributable to atrial fibrillation in middle-aged and elderly people in the Japanese general population — nineteen-year follow-up in NIPPON DATA80 -.
      ]. This was also true for the present study. However, hypertension itself could not account for the 3 times greater prevalence of AF in men than in women in the present study (Table 1, Table 2). Coronary artery disease is also known as a predisposing factor for AF [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ,
      • Kannel W.B.
      • Abbott R.D.
      • Savage D.D.
      • McNamara P.M.
      Coronary heart disease and atrial fibrillation: the Framingham Study.
      ]. Although the prevalence of coronary artery disease was not determined specifically in the present study, it was lower among patients with AF in Japan [
      • Tomita F.
      • et al.
      for the Hokkaido Atrial Fibrillation Study Group
      Prevalence and clinical characteristics of patients with atrial fibrillation. Analysis of 20,000 cases in Japan.
      ] as compared with those in the Western countries [
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ,
      The AFFIRM Investigators
      Baseline characteristics of patients with atrial fibrillation: the AFFIRM Study.
      ]. Of note is that severity of coronary artery disease is less in patients of Japan than in those of Western countries [
      • Sekikawa A.
      • Satoh T.
      • Hayakawa T.
      • Ueshima H.
      • Kuller L.H.
      Coronary heart disease mortality among men aged 35–44 years by prefecture in Japan in 1995–1999 compared with that among white men aged 35–44 by State in the United States in 1995–1998. Vital statistics data in recent birth cohorts.
      ,
      • Yokoyama M.
      • et al.
      for the Japan EPA Lipid Intervention Study Investigators
      Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis.
      ,
      GISSI-Prevenzione Investigators (Gruppe Italiano per lo Studio della Sopravvienza nell'infarto miocardico)
      Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial.
      ].
      Diabetes mellitus is associated with AF [
      • Benjamin E.J.
      • Levy D.
      • Vaziri S.M.
      • D'Agostino R.B.
      • Belanger A.J.
      • Wolf P.A.
      Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study.
      ,
      • Lip G.Y.H.
      • Varughese G.I.
      Diabetes mellitus and atrial fibrillation: perspectives on epidemiological and pathophysiological links.
      ]; this is also true for the present study. Alcohol drinking could increase the risk of AF [
      • Djousse L.
      • Levy D.
      • Benjamin E.J.
      • et al.
      Long-term alcohol consumption and the risk of atrial fibrillation in the Framingham study.
      ]. Although Ohsawa et al. failed to show this finding [
      • Ohsawa M.
      • et al.
      for the NIPPON DATA80 Research Group
      Mortality risk attributable to atrial fibrillation in middle-aged and elderly people in the Japanese general population — nineteen-year follow-up in NIPPON DATA80 -.
      ], the present study showed prevalence of drinkers was slightly higher in men with AF than in those without AF.
      Taken together, it seemed difficult to explain the difference of AF prevalence between Western countries and Japan and also between men and women in the present study only with these clinical characteristics.

      4.4 Methodological considerations

      The present study is limited for several reasons. First, not all community residents and company employees undergo the annual health examination. In 1998, approximately 65% of Japan's population 40 years old or more underwent an annual health examination [
      The Ministry of Health, Labor and Welfare, Japan. Statistical database.
      ]. Among company employees, 73% underwent an annual health examination [
      The Ministry of Health, Labor and Welfare, Japan. Statistical database.
      ]. Some community residents who go to a hospital regularly for treatment tend not to undergo the health examination provided by their local government. This could lead to underestimation of the prevalence rate of AF for community residents. Second, the present study was cross-sectional in nature; therefore, the number of people having paroxysmal AF may be underestimated as mentioned above. Third, there could be a seasonal variation in frequency of episodes of paroxysmal AF [
      • Watanabe E.
      • Kuno Y.
      • Takasuga H.
      • et al.
      Seasonal variation in paroxysmal atrial fibrillation documented by 24-hour Holter electrocardiogram.
      ]. The annual health examination is carried out through the whole year, and therefore, possible seasonal variation of AF episodes would have affected the present data. Finally, only prevalence of AF was determined for each 10-year age group, and a complete dataset of clinical characteristics was available from approximately a sixth of the subjects; therefore, detailed analyses to determine independent predictors of AF were not performed in the present study.

      5. Conclusions

      Although limited for these reasons, the present study, based on the data of annual health examinations of more than 600,000 people, showed the rate of AF increased as the population aged in Japan, as in Western countries. The prevalence of AF was approximately two thirds of that in the USA [
      • Feinberg W.M.
      • Blackshear J.L.
      • Laupacis A.
      • Kronmal R.
      • Hart R.G.
      Prevalence, age distribution, and gender of patients with atrial fibrillation.
      ], and the projected increase in the number of people having AF in Japan is modest when compared with that of the USA [
      • Go A.S.
      • Hylek E.M.
      • Phillips K.A.
      • 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.
      ,
      • Miyasaka Y.
      • Barnes M.E.
      • Gersh B.J.
      • et al.
      Secular trends in incidence of atrial fibrillation in Olmsted County, Minnesota, 1980 to 2000, and implications on the projections for future prevalence..
      ] in the year of 2050.

      Acknowledgements

      This study was conducted with the support of the Japanese Society of Circulation.
      The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [
      • Coats A.J.
      Ethical authorship and publishing.
      ].

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