The associated cardiovascular diagnoses were hypertension in
The associated cardiovascular diagnoses were hypertension in 59.1% of the patients, coronary artery disease in 10.1%, cardiomyopathy in 8.3%, valvular casein kinase disease in 13.7%, and artificial cardiac valves in 3.1%. Thus, hypertension was the most common underlying disease in patients with AF (Table 4) , which is consistent with the results of the J-RHYTHM study (42.8%)  and various other previous investigations [7,16,41–44]. In addition, hypertension was the most common factor as a component of the CHADS2 score. Since blood pressure-lowering therapy per se can contribute to inhibiting the new-onset or recurrence of AF and prevent strokes, hypertension is thought to be an extremely important therapeutic target for the management of patients with AF.
Assuming that the incidence of cerebral infarction has the same person-years value for each CHADS2 score, as reported by Gage et al. , i.e., 1.9% with a score of 0 and 2.8% with a score of 1, the number of patients suffering from a cerebral infarction among the patients registered in the J-RHYTHM Registry is projected to be 24 with a score of 0 and 76 with a score of 1, despite the fact that these patients are evaluated to be in a low-risk group. The scale of these numbers cannot be ignored, because the total number of patients with a CHADS2 score of 0 or 1 is very large in Japan. Since a cardiogenic stroke is likely to be severe, and its severity is not always in proportion to the CHADS2 score, interventions to prevent stroke should be considered even in the patients in a low-risk group, i.e., those with a CHADS2 score of 0 or 1. Anticoagulation therapy for these low-risk patients can be performed referring to a new score for further risk stratification, such as the CHA2DS2-VASc score .
Conflict of interest
Effects of the maze procedure and guidelines The prevention of stroke has been recognized as an important reason for performing the maze procedure since the era of the cut-and-sew technique . Lall et al.  demonstrated that the early results, such as 30-d mortality, early atrial tachyarrhythmias, late stroke, and survival, after the maze procedure with a bipolar RF ablation device were similar to those with the cut-and-sew technique. Beukema et al.  examined the intermediate to long-term results after the maze procedure with an irrigated unipolar RF ablation device in 258 patients with structural heart disease and permanent AF. Oral anticoagulation drugs were taken by 99% of these patients. Stroke was reported in 4 patients. The mortality rate was 28.3% during a mean follow-up of 43.7±25.9 months. The postoperative rhythm was not predictive of all-cause mortality, cardiac mortality, and stroke. Kim et al.  investigated whether the type of the mitral surgery affects the outcome in 435 patients who underwent the maze procedure concomitant to either a mitral repair or mitral replacement. No significant differences were found between the types of mitral surgery in terms of survival, stroke incidence, or sinus rhythm restoration rate. More recently, Fujita et al.  evaluated the long-term outcomes of a combined mitral repair and maze procedure for patients with nonrheumatic mitral regurgitation and chronic AF. The 15-year survival was 71%, and 11 thromboembolic episodes were detected during a mean follow-up period of 7.4±4.3 years, of which 7 occurred in patients with recurrent AF (Fig. 1). A guideline for AF surgery was published by the Japanese Circulation Society in 2000, and revised in 2011 . The guideline focused on the prevention of stroke and the complications associated with AF and was constructed on the basis of the evidence obtained from previous maze procedures. Surgery for AF in patients undergoing surgery for mitral valve disease is recommended as a class 1 indication because multiple studies have demonstrated a significantly lesser incidence of stroke in patients undergoing a concomitant maze procedure compared with those without. In AF patients undergoing other cardiovascular surgeries, AF surgery is recommended as a class IIa indication.