The association between admission time and in-hospital mortality in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention: a retrospective cohort study

Introduction

Timely reperfusion is the most critical determinant of clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI) (1). Consequently, international guidelines underscore the necessity of rapid coronary revascularization via primary percutaneous coronary intervention (PPCI), with Door-to-Balloon (D2B) time serving as a fundamental benchmark for quality of care. Given the time-critical nature of myocardial ischemia, healthcare systems must ensure the delivery of consistent and expedited reperfusion therapy irrespective of the time of presentation.

However, maintaining uniform performance across different admission times remains challenging for many healthcare systems. Several studies have described a potential “off-hour effect,” in which patients admitted during nights, weekends, or public holidays experience longer treatment delays and adverse clinical outcomes compared to those admitted during regular on-hours (2-5). Nevertheless, the evidence remains inconsistent, with some studies reporting no significant differences in mortality after adjustment for clinical and organizational factors (6,7). Several hypotheses have been proposed to explain the differences between these findings, including variations in physician experience, limited access to specific treatment modalities, and lower staffing levels during off-hours (8-11). Despite numerous initiatives aimed at optimizing the quality of treatment and reducing the reperfusion time for STEMI patients, a significant proportion of patients still do not receive therapy within the recommended D2B timeframe.

Notably, most existing data originate from developed nations with emergency infrastructures and socioeconomic conditions that differ markedly from those in Vietnam. While the majority of Vietnamese cardiovascular centers currently implement 24/7 PPCI strategies for STEMI, the geographic density of such facilities remains sparse, particularly at the provincial level. This underscores the need for local, context-specific evidence to inform policy and clinical guidelines. Although such data could significantly shift practice patterns across all levels of healthcare, evaluated research within the context remains limited.

Therefore, this study aimed to evaluate the association between admission time and in-hospital mortality among STEMI patients at Thanh Hoa General Hospital. We present this article in accordance with the STROBE reporting checklist (available at https://jeccm.amegroups.com/article/view/10.21037/jeccm-2026-0021/rc).

Methods

Study design and setting

This study was conducted between April 2023 and December 2024 at the Cardiology department of Thanh Hoa General Hospital—a tertiary referral center in Central Vietnam with 24-hour PPCI capability. Data were extracted from electronic medical records and supplemented by interviews with patients or their legal representatives to ensure clinical history accuracy.

Study participants

Participants were recruited based on the following inclusion criteria:

• Vietnamese patients over 18 years old.
• Diagnosed with acute STEMI according to the 2023 European Society of Cardiology (ESC) guidelines: STEMI was defined as the presence of ischemic symptoms consistent with acute myocardial infarction accompanied by persistent ST-segment elevation on electrocardiography (≥1 mm in at least two contiguous limb leads or ≥2 mm in at least two contiguous precordial leads) or new left bundle branch block, together with elevation of cardiac biomarkers (troponin I) above the upper reference limit.
• Voluntarily agreed to participate in the study and underwent emergency coronary angiography and PPCI.

The exclusion criteria included:

• Incomplete or missing key data required for the analysis (e.g., admission time, in-hospital outcome, or procedural information).
• Discharged against medical advice or transferred to another hospital before the in-hospital outcome could be determined.

Data collection instruments

Demographic information

Baseline demographic information included age, sex, place of residence (urban or rural), and relevant medical history such as hypertension, diabetes mellitus, smoking status, previous cardiac intervention, and heart failure.

Admission time

Admission time was divided into on-hours and off-hours based on the working schedule of Vietnamese hospitals. On-hours are defined as 7:00 AM–5:00 PM, Monday to Friday, and off-hours are from 5:01 PM to 6:59 AM on weekdays, all hours on weekends, and public holidays, reflecting the standard staffing shifts in Vietnamese public hospitals. During on-hours, the catheterization laboratory operates with a full in-house multidisciplinary team, whereas during off-hours, emergency PPCI services remain available 24/7 through an on-duty team and an on-call system. Although catheterization laboratory and imaging services are available at all times, activation of the on-call team may contribute to differences in workflow and treatment intervals.

Clinical characteristics and angiography results

Clinical variables included systolic and diastolic blood pressure at admission, Killip classification, and the occurrence of pre-hospital cardiac arrest.

Angiographic variables included the number of damaged coronary vessels and the identification of the culprit coronary artery.

In-hospital death was defined as death due to cardiac causes occurring during the index hospitalization, before hospital discharge. Cardiac causes included fatal myocardial infarction, cardiogenic shock, fatal arrhythmias, mechanical complications of myocardial infarction, heart failure, or other cardiovascular causes.

D2B time

D2B time was defined as the interval between hospital admission and the first balloon inflation during PPCI. D2B time segments included:

• Door-to-Cathlab: time calculated from patient admission to transfer to the intervention room.
• Cathlab-to-Balloon: from patient arrival at the intervention room to angioplasty for revascularization.

D2B time was calculated as the sum of Door-to-Cathlab time and Cathlab-to-Balloon time.

Delayed D2B time (>120 minutes): as our patients were initially admitted to primary care hospitals without PCI capabilities, and considering the specific healthcare context in Vietnam, delayed D2B time was defined as >120 minutes, in accordance with the 2023 ESC recommendation for first medical contact First Medical Contact-to-Device (FMC-to-device) time in transferred patients (1).

Interventions methods

Patients were categorized into stent implantation and non-stent intervention groups. Stent implantation refers to any procedure that involves the placement of at least 1 stent. The non-stent group included balloon angioplasty alone, thrombus aspiration without stent implantation, and procedures in which definitive stent deployment was deferred or deemed inappropriate. Patients who did not receive stent implantation generally represented more complex clinical or angiographic scenarios. These included extensive thrombus burden, severe diffuse coronary disease without suitable landing zones, small vessel diameter, unsuccessful lesion crossing, residual uncertainty regarding vessel anatomy, or cases where only thrombus aspiration and/or balloon angioplasty was performed. In some patients, procedural instability or poor clinical condition also influenced treatment decisions.

Recruitment and data collection

A consecutive sampling strategy was employed. In practice, the sample consisted of all 201 patients with acute STEMI admitted to the Thanh Hoa General Hospital, and underwent PPCI during the time of the study. The patients’ follow-up treatment and in-hospital deaths were recorded. The overall study design and patient selection process are shown in Figure 1.

Figure 1 Research process flowchart. PPCI, primary percutaneous coronary intervention; STEMI, ST-segment elevation myocardial infarction.

Statistical analysis

Statistical analyses were performed using RStudio (version 4.5.2). Continuous variables were presented as mean ± standard deviation (SD) or median [interquartile range (IQR)] and compared using Student’s t-test or Mann-Whitney U test based on the Shapiro-Wilk normality test. Categorical variables were compared using Chi-squared or Fisher’s exact test.

To identify predictors of in-hospital mortality, Firth regression was chosen to minimize bias associated with the limited number of mortality events (n=11). Variables included in the regression analyses (intervention method, D2B time, age, systolic blood pressure, and Killip classification) were selected based on existing clinical evidence. Continuous variables were modeled as linear terms. Formal assessment of nonlinear relationships (e.g., using restricted cubic splines or fractional polynomials) was not performed because of the limited number of outcome events.

Statistical significance was defined as P<0.05.

Ethical consideration

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Thanh Hoa Provincial Department of Health (approval No. 2779/SYT-NVY). Informed consent was obtained from all participants. All responses were anonymised to ensure confidentiality and used solely for research purposes.

Results

Table 1 illustrated the demographic characteristics of the participants in the study. A total of 201 patients with STEMI undergoing primary PCI were included, of whom 94 (46.8%) were admitted during on-hours and 107 (53.2%) during off-hours. Overall, 11 patients (5.5%) died during hospitalization, while 190 (94.5%) survived to discharge. The majority of patients were male (64.9% vs. 75.7%, P=0.09) and resided in rural areas (81.9% vs. 83.2%, P=0.81).

The proportion of patients under 60 years old was higher in the group of patients admitted during off-hours (P=0.03). No statistically significant differences were found in gender, current residence and medical history across the on-hours groups.

Table 2 presented clinical characteristics of patients by in-hospital mortality. The results revealed statistically significant differences between diastolic blood pressure, Killip classification, and pre-hospital cardiac arrest among patients. Patients with Killip classification III/IV (P<0.001), and pre-hospital cardiac arrest (P=0.008) had a higher in-hospital mortality rate compared to the other group. Furthermore, diastolic blood pressure tended to be lower in patients who died in the hospital (69.5±11.1 and 77.3±10.3, P=0.01). In addition, no statistically significant differences were found between number of damaged coronary vessels (P=0.52) and culprit coronary artery (P=0.63).

The treatment time intervals are presented in Table 3. Door-to-Cathlab and D2B times were significantly longer among patients admitted during off-hours than among those admitted during on-hours. However, there was no statistically significant difference in Cathlab-to-Balloon time between the two groups (P=0.13). The number of patients that had delayed D2B time and in-hospital mortality also showed no significant distinction.

Based on the results of existing clinical evidence, we chose five predictors to the regression model with in-hospital mortality as the outcome. Table 4 showed Firth’s penalized logistic regression, which is used to reduce the small-sample bias of in-hospital death data. Among the included variables, intervention methods were significantly associated with the outcome. Non-stent intervention was independently associated with significantly increased odds of in-hospital mortality. D2B time was not significantly associated with in-hospital mortality. Similarly, age, systolic blood pressure and Killip classification were not significantly associated with in-hospital mortality in the multivariable model.

Discussion

Demographic information and clinical characteristics

Our analysis showed few significant differences in baseline characteristics between patients admitted during on-hours and off-hours. Most characteristics were comparable, except for age, while diabetes and pre-hospital cardiac arrest were significantly more frequent among patients who died during hospitalization.

Patients aged ≤60 years were more commonly admitted during off-hours than on-hours (28.0% vs. 14.9%, P=0.03), which may reflect differences in healthcare-seeking behavior or work-related schedules. Similar patterns have been reported in previous studies of acute cardiovascular care (3,12).

Diabetes mellitus is a well-established risk factor for cardiovascular morbidity and mortality (13-15). In addition, patients with both diabetes and cardiovascular disease tend to experience poorer clinical outcomes (16). Our findings are consistent with this evidence, highlighting diabetes as an important characteristic among patients with fatal outcomes. Particular attention should be given to this high-risk group, along with public education strategies to improve patient awareness of the relationship between diabetes and cardiovascular disease.

Our study included a relatively low proportion of patients with Killip class III–IV. This may reflect the inclusion of only STEMI patients who underwent emergency coronary angiography and PPCI, excluding those who died before catheterization or were unsuitable for invasive treatment because of severe hemodynamic instability. In addition, our hospital’s 24/7 PPCI program may facilitate earlier reperfusion and reduce progression to advanced heart failure, while the small sample size may have further limited the representation of severe cases.

Pre-hospital cardiac arrest was also associated with in-hospital mortality in our cohort. Cardiac arrest is a major contributor to mortality in STEMI because of systemic ischemia–reperfusion injury affecting multiple organs, particularly the heart and brain (17). Consistent with our findings, Omer et al. reported that cardiac arrest was associated with increased short-term mortality, especially when accompanied by cardiogenic shock (18).

Time segments before cardiac intervention

Patients admitted during on-hours had significantly shorter Door-to-Cathlab and overall D2B times than those admitted during off-hours, whereas Cathlab-to-Balloon time did not differ significantly. These findings are consistent with previous studies by Cubeddu et al. [2009], Tang et al. [2017], and Tscharre et al. [2017] (19-21). The contribution of each time segment is critical to the overall D2B interval. The Door-to-Cathlab phase may be prolonged by several subjective and pre-hospital factors, including limited patient awareness of acute coronary syndrome symptoms, delays in ambulance response and delays related to family decision-making. Prolongation of this segment directly contributes to increased D2B time and a higher likelihood of D2B delay. Moreover, substantial differences in D2B times across countries suggest that pre-hospital delay remains a common challenge for STEMI management worldwide. Previous studies have indicated that patient recognition of cardiac symptoms, utilization of Emergency Medical Services, and traffic conditions may contribute to the differences in D2B times observed between on-hours and off-hours admissions (22).

Notably, the median D2B times in the present study were 194 and 260 minutes for on-hours and off-hours admissions, which greatly exceeds the 120-minute threshold recommended by the 2023 ESC guidelines for first medical contact FMC-to-device time in transferred patients (1). This duration is also longer than that reported in previous studies conducted in Vietnam (Lợi et al., 2023) as well as in other countries such as Oman (Al-Rumhi et al., 2024), the United States (Bloos et al., 2021), and Thailand (Tungsubutra et al., 2019) (8,23-25). These findings underscore persistent challenges in STEMI care, highlighting the need to improve public awareness of STEMI symptoms and promote earlier access to emergency medical care (26).

Although overall D2B times differed significantly between on-hours and off-hours admissions, the rate of D2B delay did not differ significantly between the two groups (P>0.05). This observation suggests that, in addition to patient- and family-related factors, in-hospital contributors to reperfusion delay should also be investigated. Further studies are needed to identify and address these factors in order to implement effective strategies for reducing D2B time.

Predictors of in-hospital mortality

Our use of Firth penalized regression provides a robust analytical framework, particularly in datasets with relatively small event numbers where conventional logistic regression may be biased. The results identified intervention strategy as the only factor significantly associated with in-hospital mortality in the multivariable model, while D2B time and other baseline clinical variables were not significantly associated with mortality. Our analysis demonstrated that patients treated with non-stent interventions (balloon angioplasty, thrombectomy) had a markedly higher risk of in-hospital mortality compared with those undergoing stent implantation [odds ratio (OR) =6.07; 95% confidence interval (CI): 1.95–24.66]. This finding is consistent with the established role of coronary stenting in restoring durable epicardial coronary flow and preventing recurrent vessel occlusion in acute myocardial infarction. Randomized trials and registry analyses have shown that stent implantation during primary PCI improves procedural success and reduces major adverse cardiac events compared with balloon angioplasty or incomplete revascularization strategies (27). For example, a multicenter randomized study of STEMI patients demonstrated significantly lower rates of major adverse cardiovascular and cerebrovascular events among patients treated with stent implantation compared with non-stenting approaches at 12 months (28). The findings suggest that while stenting remains the standard reperfusion strategy in STEMI, the observed association between non-stent intervention and mortality in our cohort likely reflects underlying disease severity, procedural complexity, or incomplete revascularization rather than the absence of a stent. Patients undergoing non-stent procedures often presented with more severe coronary anatomy, larger thrombus burden, hemodynamic instability, cardiogenic shock, or technically challenging lesions. Therefore, non-stent intervention may serve as a surrogate marker of disease severity rather than an independent causal factor.

Contrary to conventional expectations, D2B time was not independently associated with in-hospital mortality in our multivariable model. Although rapid reperfusion remains a cornerstone of STEMI management, the relationship between D2B time and mortality may be attenuated after adjustment for clinical risk factors. Contemporary registry data involving more than 13,000 STEMI patients demonstrated that while shorter D2B times were associated with lower unadjusted mortality, this association was not consistently significant after multivariable adjustment in lower-risk patients (29). Furthermore, several studies have shown that although shorter D2B times improve coronary reperfusion and reduce early complications, improvements in system-level metrics alone may not translate into proportional reductions in mortality (30). This observation underscores the multifactorial nature of outcomes in acute myocardial infarction.

Although age, systolic blood pressure and Killip classification are well-established prognostic indicators in acute myocardial infarction, their lack of statistical significance in the analysis likely reflects the limited number of mortality events.

Age is widely recognized as one of the strongest predictors of mortality in acute coronary syndromes, with older patients exhibiting higher rates of complications and death due to increased comorbidity burden, frailty, and reduced physiological reserve. However, in smaller cohorts or analyses with few outcome events, the independent effect of age may be attenuated after adjustment for other clinical variables, particularly when age correlates with hemodynamic instability or comorbid conditions (31).

Similarly, admission blood pressure has long been considered an important marker of hemodynamic status in acute myocardial infarction (32). Hypotension often reflects cardiogenic shock and is associated with more fatal outcomes. Nevertheless, systolic blood pressure alone may not fully capture the complexity of hemodynamic compromise, which is influenced by multiple factors including ventricular function, infarct size, and systemic vascular resistance. Consequently, the prognostic value of blood pressure may be reduced when more comprehensive clinical indicators are considered.

The Killip classification remains a simple yet essential clinical tool for assessing patients with acute myocardial infarction. Empirical studies have demonstrated a strong stepwise increase in mortality across Killip classes, and it remains a key component of contemporary risk scores and guideline recommendations (33,34). However, in our study, Killip class did not emerge as an independent predictor after multivariable adjustment. This finding contrasts with results reported in several previous studies. This finding may be attributable to the relatively small sample size or limited number of patients in higher Killip classes.

Limitations

Our study has several limitations. First, the study was conducted at a single hospital with a relatively small sample size, making it difficult to avoid selection bias. Therefore, conducting studies in other hospitals in Vietnam would help generalize the results. Second, although Firth penalized regression was used to reduce small-sample bias, the limited number of in-hospital deaths may still have resulted in imprecise estimates and limited statistical power. Third, one of the primary goals of emergency reperfusion in STEMI is the preservation of viable myocardium and the prevention of post- infarction heart failure, left ventricular aneurysm, though post-discharge follow-up data or long-term major adverse cardiovascular events outcomes were not available in the study. Finally, the relatively small number of in-hospital deaths limited the complexity of the regression analyses. Continuous variables were modeled as linear terms, and potential nonlinear relationships could not be formally evaluated. Therefore, the estimated associations should be interpreted with caution and warrant confirmation in larger studies.

Conclusions

The study offers one of the first comprehensive assessments of association between admission hour and in-hospital mortality rate in Vietnam. The results showed significantly longer reperfusion times in the off-hours group compared with the on-hours group, particularly for D2B time. However, regarding clinical outcomes, the study found no statistically significant difference in in-hospital mortality rates between the two groups. Although no clear differences in patient outcomes according to admission hour were observed in this study, these findings are exploratory and should be interpreted with caution. Larger multicenter studies are needed to confirm these observations and evaluate potential regional differences, particularly in in-hospital mortality.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jeccm.amegroups.com/article/view/10.21037/jeccm-2026-0021/rc

Data Sharing Statement: Available at https://jeccm.amegroups.com/article/view/10.21037/jeccm-2026-0021/dss

Peer Review File: Available at https://jeccm.amegroups.com/article/view/10.21037/jeccm-2026-0021/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jeccm.amegroups.com/article/view/10.21037/jeccm-2026-0021/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Thanh Hoa Provincial Department of Health (approval No. 2779/SYT-NVY). Informed consent was obtained from all participants. All responses were anonymised to ensure confidentiality and used solely for research purposes.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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