Atrial fibrillation (AF) is the most common arrhythmia in clinical practice, and is associated with an increased risk of cerebral infarction, heart failure, and overall mortality. Recently, AF has been attracting attention, due to its increased treatment options by release of novel oral anti-coagulants. Nevertheless, the important concept of the management of AF remains to be its prevention. Therefore, identification of risk factors is important, especially in the real world clinical practice.

In Japan, the number of patients with AF and the prevalence are on the increase, and are estimated to exceed one million by 2050 [1]. Diabetes is also on the increase just as AF, and is likely to exceed 30 million by 2018. It is important to prevent the onset of cerebral infarction in the management of patients with AF. As for the CHADS2 score which is known as a risk factor of cerebral infarction [2], it is evident that diabetes is the second most important factor following age [3]. The influence of diabetes becomes larger especially when the disease duration prolongs to 8 to 10 years. The risk factors of the onset of AF have long been studied so far. And one of the old but good examples is Framingham study, in which diabetes is considered as one of the significant risk factors (odds ratio (OR): 1.4 for men and 1.6 for women) [4].

Recent meta-analysis has reported that diabetes can be a risk factor of AF [5]. However, some studies have reported conflicting findings [6,7], partly because most of these studies are case-control studies that are likely to be biased. Although there have been reports of large-scale study, most of them are based on community-based medical checkup [8]. To our knowledge, there has been no report of the large-scale study from the real world clinical practice. Therefore, this conclusion is not fully agreed. We worked on the issue, because we are from one of the hospitals that hold the largest number of diabetic patients in Japan.

Although several reports have reported an association between DM and AF, the results have been controversial and no large scale study has been reported in the real world clinical practice. To our knowledge, this is the first study which revealed the association in a large scale in the real world clinical practice.

Diabetes is important as one of the risk factors of the AF. Therefore, preventative treatment intervention is recommended, because the prognosis of asymptomatic patients with AF is poor. Early detection of the AF by periodical examination such as electrocardiography might be useful for the prevention of the onset of cerebral infarction for the patients with diabetes as well.

In general, onset frequency of the AF increases with the duration of DM.  In many cases of DM, we found that paroxysmal AF tends to shifts to sustained AF, and finally to chronic AF. This is consistent with the experimental findings that atrial electromechanical function is impaired in diabetic rabbits, and is associated with atrial fibrosis and interatrial electrical conduction delay, promoting the onset of AF [9-11].

In conclusion, we demonstrated for the first time in a large scale investigation in Japan that DM would significantly increase the risk of the onset of AF. Therefore, it is recommended that patients with DM should take electrocardiography regularly and be intervened at an early stage in the real world clinical practice.