Objectives: To describe the relation between the Arctic Oscillation (AO) index and the incidence and mortality in acute myocardial infarction (AMI) in the northern, partly subarctic area of Sweden.
Design: Comparison of a time series of daily variations in the AO index and register data on the daily number of fatal and nonfatal AMIs.
Setting: The northernmost two Swedish counties, Norrbotten and Västerbotten.
Subjects: All inhabitants in the Norrbotten and Västerbotten counties were followed for the occurrence of an AMI between 1985 and 1999 within the framework of the WHO MONICA (multinational MONItoring of trends and determinants of CArdiovascular disease) Project.
Main outcome measure: Fatal and nonfatal AMIs.
Results: There was a consistent positive relation between increasing AO index and an increase in AMI incidence and mortality. The maximum impact on AMI incidence of the AO came after a lag phase of 3 days. A one unit increase in AO index was associated with an increase in: the daily number of AMIs (+3.8%), the case fatality in AMI within 28 days (+5.1%), the number of nonfatal AMIs (+3.4%), and the number of sudden cardiac deaths (+8.3%).
Conclusions: An AO index increase, bringing warmer weather over Scandinavia, was associated with an increase in the incidence and mortality in AMI in northern Sweden.