The incidence of AF in Japan was also reported
The incidence of AF in Japan was also reported from an early cohort of the Hisayama Study  in the period between 1961 and 1984. Similar to the reports from Western countries, the incidence of AF increased with age in both men and women (Fig. 7) . In a recent report of an observational cohort study based on an annual health check-up program in Niigata and including 28,449 participants aged 20 years or older (mean 59.2 years), the incidence of AF per 1000 person-years was 4.1 in men and 1.3 in women . In another community-based study with 30,010 participants aged 40 years or older (median 73 years) based on an annual health survey in Kurashiki , the incidence of AF per 1000 person-years seemed to be higher (13.0 in men and 7.4 in women), but that in the lowest age tertile (≤67 years) was comparable (5.3 in men and 1.5 in women) with that in Niigata .
Ethnicity and AF Most of the epidemiological data about AF from the Western countries have been derived from predominantly white populations. Therefore, the prevalence of AF among groups of different ethnicities or races should be evaluated with caution, since the world literature on the clinical epidemiology of AF in non-white groups is limited. Ethnic differences in cardiovascular disease and stroke have been reported by Balarajan , in which a higher prevalence of ischemic p-Cresyl sulfate disease and hypertension was noted in Indo-Asian populations and Afro-Caribbean populations, respectively. A small number of reports on the prevalence of AF in the other populations can also be found, which show differences in the mean age and the most common etiological causes of AF. For example, Maru  reported a survey of 136 Ethiopian cardiac outpatients with AF in whom the mean age was 41 years, and the common etiological causes of AF were rheumatic heart disease (66%), hypertension (10%), cardiomyopathy (9%), and ischemic heart disease (7%). In contrast, in a review of 291 predominantly Chinese patients with AF who were treated at a regional hospital in Hong Kong , the mean age was 73 years, and the common etiological factors were hypertension (29%), vascular disease (25%), and rheumatic heart disease (18%) . In another survey of acute medical admissions for AF at a city center hospital in Birmingham, UK,  serving a multi-ethnic population of 300,000 (64% white, 11% black/Afro-Caribbean, 25% Indo-Asian), 87% of the patients with AF were white, 4% were black/Afro-Caribbean, and 9% were Indo-Asian, indicating that there was a lower prevalence of AF in Indo-Asians compared to whites . In that survey , the predominant etiological factor associated with AF in black/Afro-Caribbeans was hypertension (50%), whereas in Indo-Asians, it was ischemic heart disease (45.5%). However, this trend has changed in Japanese patients with AF, since the predominant etiological factor according to recent Japanese studies [38,39] has been hypertension, and not ischemic disease.
Epidemiology of AF and future therapeutic strategies Knowledge of the prevalence and the incidence of AF from epidemiological surveys in general populations is important, and knowledge of the characteristics of patients who have already been diagnosed with AF and are receiving treatment is also necessary for general physicians in order to ensure that optimal medical care can be provided for these patients. Data obtained at the time of registration in the J-RHYTHM Registry  are currently available to provide information about Japanese AF patients. The J-RHYTHM Registry  is a multicenter prospective observational study that is being performed to investigate the present status and optimal intensity of anticoagulation in Japanese patients with AF. Registration was terminated in July 2009. A total of 7937 patients with AF from 158 institutions, including 5468 men (68.6±10.0 years) and 2469 women (72.2±9.0 years), were registered. Of these, 34.2% were over the age of 75 years. The type of AF was paroxysmal in 37.1%, persistent in 14.4%, and permanent in 48.5%. Overall, 87.3% of patients were taking warfarin (2.9±1.2mg/day), including co-administration with aspirin. The CHADS2 score  was in 15.7% of the patients, 1 in 34.0%, and ≥2 in 50.3%, respectively, indicating that almost half (49.7%) of the patients were in a low-risk group for stroke.