Circadian variation of onset of acute myocardial infarction (AMI) has been noted in many studies, but there are no data about subgroups of patients with previous coronary artery bypass grafting (CABG). Because of abnormalities in the circadian rhythm of autonomic tone after surgery, it was very interesting to analyze the circadian patterns in the onset of symptoms of AMI in various subgroups of 1784 patients with previous CABG. As in the other studies, a peak occurred in the morning hours with 26.3% of the patients, but there was a second nearly equal, but higher, peak (26.4%) in the evening hours. The subgroups with specific clinical characteristics exhibited different patterns that determined these peaks in all populations. In patients older than 70 years of age, in both sexes, in smokers, diabetics, in patients with hypertension, in those undergoing beta-blocker therapy, and in patients without previous angina, two nearly equal peaks were observed, with higher evening peaks, except in those patients with hypertension and without angina. Only one peak in the evening hours was observed in a subgroup of patients with previous congestive heart failure (CHF) and non-STEMI. The subgroup of patients with previous angina and previous AMI exhibited no discernible peaks. The distribution of time of onset within the four intervals was not uniform, and the difference was statistically significant only for patients undergoing beta-blocker therapy at time of onset (p = 0.0013), nonsmokers (p = 0.0283), and patients with non-STEMI (p = 0.0412). It is well known that patients with AMI have a dominant morning peak of circadian variation of onset. However, analyzing a different subgroup of patients with AMI after previous CABG, it was found that some subgroups had two peaks of onset, but a higher evening peak (patients older than 70 years of age, smokers, diabetics, and a group of patients who were taking beta-blocker therapy). This subgroup of patients, together with the subgroups of patients with a dominant evening peak (patients with CHF and those with non-STEMI) and with patients with no peak (patients with previous angina and previous AMI), probably appear to modify characteristic circadian variation of infarction onset, expressing a higher evening peak, respectively to the previous CABG, with adverse consequences for central nervous system functioning.

INTRODUCTION Mortality in ST elevation myocardial infarction (STEMI) ranges from 4-24% and is dependent on the variety of patients' clinical characteristics (CC) that are present prior to and within the first hours of the onset of MI, affecting reliability of the diagnosis. The higher mortality rate of patients with STEMI should be associated with a higher rate of applied reperfusion therapy according to guidelines and randomized study results, which is in opposition to everyday hospital practice. OBJECTIVE The aim of this study was to analyze the mortality of STEMI patients in relationship to their clinical characteristics at presentation, their age, sex, risk factors, prior coronary disease, and time interval from symptom onset to hospital presentation, complications and administered therapy. METHOD The analysis involved patients treated in five coronary care units, four Belgrade Hospital Centres and the Belgrade Emergency Centre of the Clinical Centre of Serbia. Evaluated data was obtained from the Serbian National Registry for Acute Coronary Syndrome (REAKSS) and databases of local coronary care units (CCU). RESULTS During 2005 and 2006, a total of 2739 patients with STEMI, of average age 63.3 +/- 11.7, with 64.9% males aged 61.3 +/- 11.7 and 35.1% females aged 67.0 +/- 10.7 (p < 0.01) who underwent treatment. Most of the patients (80.5%) were distributed within the elderly groups of 60, 70 and 80 years of age, with the highest percent of mortality rate (45.9%) noted at age 80 years. Anterior localization of myocardial infarction was observed in 40.2% of patients, with lethal outcome in 21.4% patients, while 59.8% of patients suffered inferiorly localized MI with much lower mortality rate (12.2%, p < 0.01). In 2005, STEMI was registered in 48.7%, while in 2006 in 44.7% of patients. Prior angina pectoris was present in 19.9% of patients, more frequently among women (p < 0.05), prior MI in 14.5% of patients, more often among males (p < 0.05), while aortocoronary revascularization was found in 3.9% of patients. Hospital mortality rate due to STEMI was higher in the group of patients with a history of prior MI (19.1% vs. 15.7%; p > 0.05). Regarding risk factors, hypertension was present in 61.8% of patients, more often among women (69.1% vs.57.9%) (p < 0.01), carrying a higher mortality rate of 18.9% vs. 9.9% among males (p < 0.01). Hyperlipidemia was found in 31.9% of patients; more frequently among women 34.8% vs. 30.4% males (p < 0.05), as well as diabetes mellitus observed in 25.1% of patients; 22.4% males and 30.1% females (p < 0.01). 39.6% of patients were smokers; 46.9% males and 28.0% females (p < 0.01). Heart failure had 33.4% of patients; mortality rate was registered in 28.2% of patients, and was significantly higher than in the non heart failure group (7.9%, p < 0.01). Heart rhythm disorders were registered in 21.3% of patients, more frequently involving posterior MI 55.3% vs 44.7% of anterior MI (p > 0.05), and was significantly higher among females 23.5% vs. 20.1% in males (p < 0.05). In 2005 in Belgrade hospitals, reperfusion therapy (RT) was performed in 34.6% of patients, mostly as thrombolytic therapy (TT) (in 99.0% of patients), and as percutaneous coronary intervention (PCI) in 1.0% of patients. STEMI mortality rate was 12.8%. In 2006, in the CCU of the In the Emergency Center RT was applied in 48.0% of patients, TT in 13.8% and PCI in 34.2%, while classical therapy without RT was applied in 52.0% of patients. CONCLUSION Clinical characteristics significantly influence mortality in STEMI; a significantly higher mortality is among women, patients in their 80's and 90's, anterior MI localization and prior coronary disease. RT significantly lowers mortality in STEMI compared to the use of classical therapeutic approach and therefore STEMI patients with a higher mortality determined by their prehospital charactheristics, i.e. higher risk, are those who have higher benefit of RT, which should be taken into consideration when making decision about the therapy of choice.