Circadian variation in the onset of myocardial infarction: effect of duration of diabetes.

There are conflicting reports regarding circadian variation in the onset of acute myocardial infarction (MI) among patients with diabetes. We therefore, studied the circadian pattern of the incidence of acute MI in patients (n = 3,882) who were enrolled in the Onset Study stratified by the presence, type, and duration of diabetes. The Onset Study was conducted at 64 U.S. medical centers between August 1989 and September 1996. We used harmonic regression model to evaluate the circadian variation of MI symptom onset in patients with and without diabetes. Subgroup analysis was performed according to the presence, type, and duration of diabetes by the chi(2) test (dividing the day into four 6-h intervals). Patients without diabetes exhibited a prominent morning peak in the incidence of acute MI symptom onset (P < 0.001). In contrast, patients with type 1 diabetes and type 2 diabetes > or =5 years had a marked attenuation of the morning peak. Patients who had type 2 diabetes diagnosed within the previous 5 years had a pattern of onset of acute MI similar to patients without diabetes. Patients with type 1 diabetes and those with type 2 diabetes > or =5 years have an attenuation of the morning peak in acute MI. Inconsistency in observation of such an effect in patients with diabetes in the past may well have been due to difference in the duration of diabetes and thus the variable extent of underlying autonomic dysfunction.