Study design, population, and eligibility criteria

This retrospective cohort study was based on the data prospectively collected in the National Registry of Invasive Cardiology Procedures (Polish, Ogólnopolski Rejestr Procedur Kardiologii Inwazyjnej [ORPKI]). The registry was described elsewhere.⁹ All consecutive patients admitted between January 2014 and December 2017, diagnosed with acute myocardial infarction (AMI) according to the current European guidelines,^10,11 and treated with PCI were included in this study. Then, the data received from the ORPKI registry were matched with the data from the Polish National Health Fund (Polish, Narodowy Fundusz Zdrowia [NFZ]). When merging the databases, the following characteristics were considered: age, sex, catheterization laboratory, and the date of the procedure. The data analyzed here came from the Świętokrzyskie Province and included procedures carried out in the above specified period in 7 catheterization laboratories. We evaluated the subsequent follow‑up timepoints obtained from the NFZ records after 30, 183, 365, and 1095 days in order to compare them with the results of previous studies. None of the study patients were lost to follow‑up. Hospitals and catheterization laboratories participating in our study were included into the 24/7 network providing pPCI. Since the ORPKI registry is based on current clinical practice data, only standard written informed consent for PCI and data collection was obtained from the study patients. The study protocol complied with the Declaration of Helsinki.

Study definitions

Day hours were defined as the time interval between 7:00 am and 10:59 pm, whereas night hours as the time interval between 11:00 pm and 6:59 am.

Pain‑to‑balloon (PTB) time was defined as the time from the AMI symptom onset to the first inflation of a catheter balloon within the culprit lesion. All study patients were divided into groups by PTB times: patients with a PTB time shorter than 3 hours (group 1), patients with a PTB time longer than 3 hours but shorter than 12 hours (group 2), and patients with a PTB time longer than 12 hours but shorter than 24 hours (group 3). The overall group of patients with AMI was also evaluated for the type of AMI: STEMI and non–ST‑segment elevation myocardial infarction (NSTEMI). First‑medical‑contact‑to‑balloon time was defined as the time from the first medical contact of the patient with AMI to catheter balloon inflation in the culprit artery.

Primary percutaneous coronary intervention protocol

Both intervention strategy and device choice were at the discretion of the attending physician. Pharmacological treatment was administered according to current guidelines.^10,11

Study endpoints

The primary study endpoints included all‑cause mortality and major adverse cardiovascular and cerebrovascular events (MACCEs). The latter involved coronary revascularization (repeated percutaneous coronary revascularization or coronary artery bypass grafting), cerebral stroke or transient ischemic attacks, myocardial infarction, and the overall mortality rate.

Statistical analysis

Categorical variables were presented as number and percentage. Continuous variables were expressed as mean (SD) or median (interquartile range) where applicable. Normality of data distribution was assessed using the Shapiro–Wilk test. Equality of variances was evaluated with the Levene test. Differences between the 2  study groups were compared using the Student or Welch t test depending on the equality of variances for normally distributed variables. The Mann–Whitney test was used for nonnormally distributed continuous variables. Categorical variables were compared with the Pearson χ² or the Fisher exact test. Multiple group comparisons were performed using the analysis of variance or the Kruskal–Wallis test. The Tukey–Kramer honest significant difference test or the Steel–Dwass method were used for post hoc comparisons. For categorical parameters and survival analyses, the Benjamini–Hochberg procedure was applied to adjust the P value. Univariable and multivariable Cox proportional hazard models were performed to identify the predictors of MACCEs and death. Factors included in the adjusted model were as follows: admission time, type of MI, age, smoking status, hypertension, Killip class, sex, diabetes, kidney disease, previous stroke, previous MI, previous PCI, cardiac arrest at baseline, chronic obstructive pulmonary disease, treatment with acetylsalicylic acid at baseline, and Thrombolysis in Myocardial Infarction (TIMI) flow grade before and after PCI. All statistical analyses were performed with the JMP software, version 14.2.0 (SAS Institute, Inc., Cary, North Carolina, United States), and statistical tests were 2‑sided (a P value less than 0.05 was considered significant).

General characteristics

The total number of patients included in the study was 2919. Among them, there were 2462 patients treated during the day hours (84.3%) and 457 patients treated during the night hours (15.7%). The main indication for PCI was STEMI, which was reported in 1993 patients (68.3%), whereas NSTEMI was noted in 926 patients (31.7%). The PTB time of up to 3 hours (group 1) was recorded in 1000 patients (34.3%), longer than 3 hours but not exceeding 12 hours (group 2) in 1452 (49.7%), and longer than 12 hours but shorter than 24 hours (group 3) in 467 (16%).

Pain‑to‑balloon time

Patients treated for AMI, when assessed by the PTB time, were older in group 3 compared with groups 1 and 2 (P <⁠0.001). The greatest percentage of patients treated during the day hours was seen in group 3 compared with groups 1 and 2 (P <⁠0.001). Pharmacological treatment received by the study patients is presented in table 1. Patients from groups 2 and 3 were more often treated via radial access (P <⁠0.001). These and other procedural characteristics are summarized in table 2.