Acute myocardial infarction is more common in winter and more common on colder days, independent of season. Environmental temperature may play an important part in the pathogenesis of acute myocardial infarction.

Objectives: To analyse the relation between serum glucose concentration and hospital outcome across the whole spectrum of acute coronary syndromes. Methods: This was a prospective cohort study of 2127 patients presenting with acute coronary syndromes. The patients were stratified into quartile groups (Q1 to Q4) defined by serum glucose concentrations of 5.8, 7.2, and 10.0 mmol/l. The relation between quartile group and major in-hospital complications was analysed. Results: The proportion of patients with acute myocardial infarction increased incrementally across the quartile groups, from 21.4% in Q1 to 47.9% in Q4 (p < 0.0001). The trend for frequency of in-hospital major complications was similar, particularly left ventricular failure (LVF) (Q1 6.4%, Q4 25.2%, p < 0.0001) and cardiac death (Q1 0.7%, Q4 6.1%, p < 0.0001). The relations were linear, each glucose quartile increment being associated with an odds ratio of 1.46 (95% confidence interval (CI) 1.27 to 1.70) for LVF and 1.52 (95% CI 1.17 to 1.97) for cardiac death. Although complication rates were higher for a discharge diagnosis of acute myocardial infarction than for unstable angina, there was no evidence that the effects of serum glucose concentration were different for the two groups, there being no significant interaction with discharge diagnosis in the associations between glucose quartile and LVF (p = 0.69) or cardiac death (p = 0.17). Similarly there was no significant interaction with diabetic status in the associations between glucose quartile and LVF (p = 0.08) or cardiac death (p = 0.09). Conclusion: Admission glycaemia stratified patients with acute coronary syndromes according to their risk of in-hospital LVF and cardiac mortality. There was no detectable glycaemic threshold for these adverse effects. The prognostic correlates of admission glycaemia were unaffected by diabetic status and did not differ significantly between patients with acute myocardial infarction and those with unstable angina.

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Objectives-To examine the circadian, seasonal, and weekly rhythms of acute myocardial infarction, and to identify subgroups in whom the rhythms are attenuated or absent to provide further information about the mechanisms of the rhythms and the processes responsible for triggering plaque events. Design and setting-Prospective, observational study in a general hospital. Patients and methods-1225 consecutive patients admitted to a coronary care unit with acute myocardial infarction were studied. Admission rates were calculated according to the hour of the day (circadian rhythm), day of the week (weekly rhythm), and month of year (seasonal rhythm). The data were analysed for variations within the whole group and within subgroups. Results-A weekly rhythm of acute myocardial infarction could not be demonstrated but there was a trend towards higher admission rates at the beginning of the week. However, the time of onset of symptoms showed significant circadian variation for the group as a whole, peaking in the morning (P = 0.006), against an otherwise fairly constant background rate. Subgroup analysis showed complete absence of the circadian rhythm in patients who were diabetic, South Asian, or taking P blockers or aspirin on admission. Significant seasonal variation in admission rates was also demonstrated for the group as a whole with a winter peak and a summer trough (P = 0.009). Again, no seasonal rhythm could be demonstrated in patients who were diabetic, South Asian, or taking 3 blockers or aspirin on admission.Conclusions-The absence of circadian and seasonal rhythms of acute myocardial infarction in almost identical subgroups suggests that common mechanisms are involved in driving these rhythms. The autonomic nervous system is a likely candidate because the rhythms were absent in patients taking /3 blockers as well as in patients in whom derangement of autonomic function commonly occurs.