[The incidence of acute myocardial infarct during the week. A chronobiological evaluation]

Several diseases, and particularly cardiovascular affections, show a periodic fluctuation in their occurrence. We investigated acute myocardial infarction (AMI) incidence in connection with the day of the week, looking for a link with psycho-social phenomena. Eight hundred and fifty-two patients with AMI were considered: they had been admitted to the emergency department of two main towns of northeastern Italy during a calendar year. Eight hundred and seventeen (533 men, 284 women) were eligible for the purpose of this study. The time of symptom onset was recorded, cardiovascular risk factors and occupational condition were evaluated. All data were analyzed through chi-square test of uniformity and Halberg single cosinor test. No statistically significant difference from the uniform distribution appeared in acute events occurrence both in patients as a whole and in single subgroups subdivided according to gender and age. However, the preferential distribution during the days of the week was somewhat different between men (highest incidence at the extreme of the week) and women (highest incidence about mid-week). Statistically significant differences in AMI occurrence in the week were evidenced when patients were analyzed after subdivision according to their occupational condition: working subjects, in comparison with not-working individuals, showed a higher AMI incidence at the beginning of the week with respect to subsequent days. It is therefore likely that the stress associated with the return to work (according to the weekly working pattern of western society) represents an additional important cause of AMI. The mechanisms for that are only speculative.