[Myocardial infarction hospitalization by the day of the week: retrospective study]

There is in the literature some studies looking for cycles and a circadian rhythm associated with acute myocardial infarction. Several authors have pointed out a higher incidence of myocardial infarction on Mondays suggesting the existence of trigger mechanisms in the disease onset. The week day distribution of hospitalizations due to myocardial infarction and its associations with patient sex and category of hospitalization (social status) in the Ribeirão Preto area from 1987 to 1996, were studied.

A total of 173,982 hospitalizations due to heart and cerebral vascular diseases, including 5,804 cases of acute myocardial infarction, were evaluated using the medical records of the Hospital Data Center of the medical school of Ribeirão Preto, University of S. Paulo. The hospitalizations were classified as being on a private basis, through private insurance or the Unified Health System (SUS). The associations with sex, patient condition at discharge and category of the hospitalization were studied.

The distribution of hospitalizations due to heart and vascular diseases and acute myocardial infarction showed a peak incidence on Mondays, corresponding to 19.3% and 16.9% of the cases. During the weekend there was a decrease in the number of heart and vascular disease hospitalizations (8.6%) and a smaller reduction in the number of myocardial infarction cases (12.7%) which are statistically significant. In addition, there were observed differences in the distribution patterns according to the day of the week and category of hospitalization. While the SUS patients (4,120) and private insurance patients (1,225) are more likely to be hospitalized on Mondays, private patients (459) are more likely to be hospitalized on Fridays and Saturdays. There were no associations with patient sex and patient condition at discharge.