Abstract Body (Do not enter title and authors here): Introduction

Available data suggest there is some regularity in the time of the day when patients experience their first clinical symptoms (pain) of ST Elevation Myocardial Infarction (STEMI). It has been noticed that the largest number of cases of myocardial infarction are observed in the early morning. Some studies, especially in Asian populations, have found a shift into the afternoon hours. Additionally, some publications suggest the existence of secondary peaks of incidence in the evening hours. There also seems to be a relationship between night hours and the occurrence of myocardial infarctions in patients with sleep apnea. Although the risk of myocardial infarction is highest in the morning, there are differences depending on the region and population which might indicate the influence of local and individual factors on the circadian rhythm of the disease.

Objective
To analyze circadian variation of STEMI first chest pain onset occurence on one of the largest populations tested so far and to see if there is an association with time delays to Percutaneous Coronary Intervention (PCI).

Methods
Data from the Polish National PCI Registry (ORPKI Registry) on patients with confirmed STEMI diagnosis who underwent either coronary angiography and/or PCI from 2014 untill 2022 were analyzed.

Results
There were 153 543 individual patients in the analyzed time period with 68% of males. Circadian variation in the probablity of STEMI occurence in both men and women is presented in Figure 1 (p>0.05). Median time from chest pain onset to first medical contact (FMC) was 180 minutes (60-260; 95% CI) at 3 am and 90 minutes (59-196; 95% CI) at 1 pm respectively (p<0.001). Median tIme from FMC to PCI was 77 minutes (53-120; 95%CI) at 1 pm vs 87 minutes (60-140; 95% CI) at 7 am. Likewise the total time of ischemia from chest pain onset to PCI has been similiary affected. No differences in the periprocedural mortality was found. We have found no influence of diabetes, age and presence of chronic pulmonary obstructive disease on the circadian pattern. Interestingly, we have seen a circadian variation of LAD vs RCA ratio with LAD nadir at noon hours and peak during midnight and RCA the opposite (p<0.001).

Conclusiions
Strong circadian variation exists in the probablity of occurence of STEMI in both males and females with peak incidence at 8 am. STEMI chest pain onset time had influence on time delays to PCI. A circadian variaiton in LAD/RCA occlusion was observed.