CARDIOVASCULAR MEDICINE

¹ Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Japan
² Osaka Police Hospital, Osaka, Japan
³ Laboratory for Cardiovascular Diseases, SNP Research Centre, The Institute of Physical and Chemical Research (RIKEN), Tokyo, Japan
⁴ Osaka Rosai Hospital, Sakai, Japan
⁵ Kashiwara City Hospital, Kashiwara, Japan
⁶ Osaka Prefectural General Hospital, Osaka, Japan
⁷ Kansai Rosai Hospital, Amagasaki, Japan
⁸ Ishinkai Yao General Hospital, Yao, Japan
⁹ Department of Medical Information Science, Osaka University Graduate School of Medicine, Suita, Japan

Correspondence to:
Correspondence to:
Dr Hiroshi Sato, Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 565-0871, Japan;
satoz{at}medone.med.osaka-u.ac.jp

Background: Variations in the incidence of acute myocardial infarction during the week may differ between and within communities, according to lifestyle.

Objective: To identify potential triggering factors for acute myocardial infarction by examining variations in incidence in the days of the week within the Osaka area of Japan.

Patients: Of 2511 consecutive patients in this region who were admitted to hospital for acute myocardial infarction between April 1998 and March 2001 and consented to take part, 2400 who had a definitely identified time of onset were enrolled.

Results: For this group as a whole, no significant difference in incidence was noted between days of the week. However, in subgroup analyses women were shown to have significant variation through the week, peaking on Saturday with a 39% increase in relative risk (p = 0.037); working subjects showed a peak on Monday, with a 26% increase in relative risk (p = 0.038). Stratified analyses showed that in working men there was a prominent Monday peak in the onset of infarction, with a 30% increase in relative risk (p = 0.022), while in working women, there was no significant variation through the week.

Conclusions: Earlier findings of a Monday peak linked to increased physical and mental occupational stress are confirmed. There is also an increase in uncertain risk factors on Saturdays for Japanese women, possibly involving a stressful weekend burden for women. Confirmation of this finding in other communities may help identify triggers of acute myocardial infarction and be useful in prevention.

Keywords: acute myocardial infarction; weekly variation; occupational stress; Japanese women

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