Introduction: In the last 20 years the outcome of STEMI patients has improved, with better survival due to an improved pain to balloon time, better pharmaco-logical and non-pharmacological measures. There are still variables which cannot be controlled.

Objective: To identify differences in clinical picture, associated comorbidities and outcome of STEMI pa-tients induced by seasonal differences in a temperate continental climate.

Methods: We examined data from the electronic STEMI registry from a high volume PPCI center. We retrospectively analyzed data from 518 STEMI patients admitted in the last 13 months, to date (01 Jan 2018 to Feb 2019). All patients were offered coronary angio-graphy. We compared clinical and paraclinical picture, comorbidities, and outcome according to the season of presentation – December, January, February admit-tance compared with June, July, August. Variables were checked for gaussian distribution, data were analyzed using SPSS Statistics (IBM).

Results: 269 out of 518 patients presented during win-ter months (51.9%). Killip class at presentation was hi-gher for winter months (χ2=10.2, p=0.017) with signi-ficant differences for all Killip classes (K I 83.3% winter (w) vs. 92.4% summer (s), K II 8.6% w. vs. 4.4% s., K III: 3.7% w. vs. 1.2% s., K IV: 4.5% w. vs 2.0% s., p=0.04). Severity during hospitalization defined by maximal Killip class anytime during in-hospital period was hi-gher throughout winter months (χ2=9.7, p=0.021) with significant differences for all 4 Killip classes, p=0.04. In terms of comorbidities, a trend toward more frequent atrial fibrillation was registered during winter months, (5.2%) vs. 5 (2.0%), χ2=3.7, p=0.053. Myocardial dysfunction quantified by Simpson’s 2D echocardio-graphy left ventricle ejection fraction (LVEF) followed the same pattern. Severe dysfunction (LVEF <30%) was more frequent among patients admitted in winter, 61 (9.7%) vs. 39 (4.4%), χ2=5.4, p=0.020. Mortality was higher in STEMI patients admitted during winter months, 9.7% vs. 4.4%, χ2=5.4, p=0.020. The total mor-tality rate throughout the year was 7.1% (37 patients). We computed a predictive model for death in STEMI patients using stepwise logistic regression technique. The model proved to be significant for season, glycemia and creatinine level (χ2=53.3, p<0.005). It explained 28.1% of the discharge status and classified correctly 94.5% of patients, p<0.001. Patients with STEMI ad-mitted during winter months had a 2,8-fold increase in probability of death compared with summer months.

Conclusions: We studied a cohort of STEMI patients treated by PPCI. The overall mortality rate was com-parable with regional data. Worse clinical and paracli-nical picture, worse LV function, and more frequent atrial fibrillation characterize patients admitted with STEMI during winter. Their risk of death is almost 3 times higher. Based on these data, we should intensify the follow-up of high-risk patients during winter time.