Non-ST segment elevation myocardial infarction (NSTEMI) is a frequent cause of ACS and results from the partial obstruction of a coronary artery.1 In NSTEMI, there is a damage of heart muscle but without persistent elevation of ST-segment on ECG. The presentation includes symptoms such as chest pain, shortness of breath, sweating, nausea and upper body discomfort.2 The diagnosis of NSTEMI is made by physical examination, ECG and an elevation of biomarker of the heart in the blood stream, mostly troponin.3 The condition is more common in old age patients and patients suffering from diabetes, hypertension, smoking, and dyslipidemia.4

There are several early complications that may occur in patients with NSTEMI within the first 24 to 48 hours of their admittance to the coronary care unit. Among those complications include cardiac arrhythmias, which may be quite frequent and might cause hemodynamic instability if not treated urgently.5 Another possible complication may include acute heart failure due to decreased pumping capacity of the heart muscles that may cause dyspnea and pulmonary edema.6 One of the rarest but most serious complications is cardiogenic shock caused by the inability of the heart to pump sufficient amount of blood.7

The development of early complications following NSTEMI is linked with poor prognosis and the likelihood of death while being hospitalized.8 Patients having arrhythmia, heart failure, or cardiogenic shock require close monitoring and cardiac support for an extended period in the coronary care unit.9 The incidence of these complications depends on factors including individual patient's profile, severity of myocardial injury and the timing of the treatment.10 Early detection of these complications is necessary since proper intervention can save the life of the patient suffering from NSTEMI.

Although there have been many advancements in the treatment of NSTEMI, the early in-hospital complications like arrhythmias, acute heart failure and cardiogenic shock remain important causes of morbidity and mortality among patients with this condition. Determining the prevalence of these complications within 24-48 hours after admission to CCU is critical in order to address these problems on time and help reduce the number of associated cases of morbidity and mortality. In addition there is a lack of information about the early complications of NSTEMI at the local level  especially among the Pakistani population.

A cross sectional study was carried out in the Cardiology Department of Ayub Teaching Hospital, Abbottabad, from 3 March 2026 to 3 September 2026. Ethical approval was taken from the hospital ethical committee before starting the study (Ethical approval certificate No.: RC.EA-2025/137). The sample size was 315 patients and was estimated by using the WHO sample size calculator with a 95% confidence level, 2.5% margin of error and an anticipated frequency of cardiogenic shock of 5.5%.11 Patients were enrolled by non-probability consecutive sampling.

Adult patients aged 18–75 years, of both gender who were diagnosed with Non-ST Elevation Myocardial Infarction were included in the study. Patients with previous CCU admission were excluded from the study.

Non-ST Elevation Myocardial Infarction was considered in patients having chest pain for more than 20 minutes, electrocardiographic changes showing ST-segment depression with or without T-wave inversion, and raised cardiac troponin with a rise and fall pattern above the 99th percentile.

Written informed consent was obtained from all patients after explaining the purpose and benefit of the study. Patients who agreed to participate were included in the study. Demographic information including age, gender, BMI, residential status, socio-economic status was recorded.

A complete clinical assessment was performed for every patient. Clinical presentation, comorbidities, ECG findings, echocardiography results and laboratory parameters including cardiac biomarkers were documented. Patients were observed during their stay in the coronary care unit and the occurrence of early complications within the first 24–48 hours was recorded. Complications noted were included arrhythmia, acute LVF and cardiogenic shock. Treatment outcome was also assessed until hospital discharge.

Cardiogenic shock was considered when the patient had systolic blood pressure ≤90 mmHg for ≥30 minutes or required support to maintain systolic blood pressure ≤90 mmHg, along with urine output ≤30 mL/hour or cool extremities, and a cardiac index ≤2.2 L/min/m². Acute LVF was diagnosed in patients with new or existing coronary artery disease who developed sudden shortness of breath, orthopnoea, peripheral oedema, raised jugular venous pressure, reduced oxygen saturation and chest X-ray findings consistent with acute pulmonary oedema. Any abnormality of the heart rate on an electrocardiogram was referred to as arrhythmia and included rhythms which were either too fast, too slow, irregular or those arising from abnormal heart sites. The early complications were the incidence of cardiogenic shock, acute LVF or arrhythmia that occurred within 24–48 hours after admission into the CCU unit. Outcome of treatment was determined by the mortality rate of the patient.

Data were analysed by using IBM SPSS version 25. Continuous variables including age and BMI were presented as mean ± standard deviation. Categorical variables including gender, residential status, Hypertension, Hyperlipidemia, Smoking, Family history of IHD, early complications and treatment outcome were expressed as frequencies and percentages. The association between early complications and treatment outcome was determined by the Chi-square test and Fischer Exact test. Stratification of mortality with demographics was also performed and post-stratification Chi-square test was applied. A p-value of ≤0.05 was considered statistically significant.

A total of 315 patients was included in the study, having mean age of 56.50±9.59 years and mean BMI of 26.59±3.66 kg/m². Majority of patients was male 231 (73.3%) while female were 84 (26.7%). Regarding residential status, 186 (59.0%) patients belong to rural areas and 129 (41.0%) from urban areas. Hypertension was present in 195 (61.9%) patients while 120 (38.1%) was without hypertension. Hyperlipidemia found in 141 (44.8%) patients whereas 174 (55.2%) not having hyperlipidemia.

 Smoking was reported in 115 (36.5%) patients while 200 (63.5%) was non-smoker. Family history of IHD present in 81 (25.7%) patients and absent in 234 (74.3%). Diabetes mellitus found in 142 (45.1%) patients while 173 (54.9%) not having diabetes (Table-I).

Table- I: Patient Demographics.

n=315

Regarding early complications among NSTEMI patients, cardiogenic shock developed in 32 (10.20%) patients while 283 (89.80%) not developed this complication. Acute LVF was seen in 42 (13.30%) patients whereas 273 (86.70%) not developed. Arrhythmias occurred in 46 (14.60%) patients while 269 (85.40%) remain free of arrhythmias. Regarding treatment outcome, mortality was recorded in 25 (7.90%) patients while 290 (92.10%) survived (Table-II).

Table- II: Frequency of Early Complications and Treatment Outcome Among NSTEMI Patients. n=315

On association between early complications and mortality, cardiogenic shock patients had mortality of 5 (15.6%) as compare to 20 (7.1%) in patients without cardiogenic shock, which was statistically non-significant (p=0.156). Acute LVF patients showing mortality in 7 (16.7%) as compare to 18 (6.6%) in patients without acute LVF, and this association was statistically significant (p=0.025). Similarly, arrhythmias patients had mortality of 7 (15.2%) compare to 18 (6.7%) in those without arrhythmias, which was also statistically significant (p=0.048) (Table-III).

Table- III: Association Between Early Complications and Treatment Outcome (Mortality).

*Chi-square Test, **Fischer Exact Test

On stratification of mortality with demographic and clinical factors, none of the factor showing statistically significant association with mortality, as all p values was greater than 0.05, including age, gender, BMI, hypertension, hyperlipidemia, smoking, family history of IHD and diabetes mellitus (Table-IV).

Table- IV: Stratification of Mortality with Demographic and Clinical Factors.

*Chi-square Test

Findings of present study showing that cardiogenic shock, acute LVF and arrhythmias was common complications occurring in significant proportion of patients, with mortality being notably higher in patients who developed these complications. Cardiogenic shock developed in 32 (10.20%) patients and mortality among these patients was 5 (15.6%) as compare to 7.1% in those without shock, though this difference not reach statistical significance. This result is scientifically based on the concept that cardiogenic shock is indicative of severe myocardial injury and myocardial pump dysfunction leading to compromised coronary perfusion, creating a vicious cycle of ischemia; yet, the limited number of cases of cardiogenic shock in the current sample size may hinder the detection of significance.

Acute LVF was observed in 42 (13.30%) patients and mortality was significantly higher, 16.7% versus 6.6% in patients without LVF (p=0.025). This can be explained as LVF indicate substantial loss of functioning myocardium following infarction, resulting in reduced cardiac output, pulmonary congestion and increased haemodynamic stress on already compromised heart, all of which predisposing towards higher mortality risk.

Present study showing cardiogenic shock in 32 (10.2%), acute LVF in 42 (13.3%) and arrhythmias in 46 (14.6%) of NSTEMI patients, with overall mortality of 25 (7.9%). These finding closely resemble that of Hussain et al. 12 who reported cardiogenic shock in 17 (8.4%) NSTEMI patients, and Sikandari et al. 11 who found heart failure in 15.2%, mortality in 12.1% and cardiogenic shock in only 5.5% of patients undergoing early PCI, suggesting comparable complication burden when patients receiving timely intervention. In contrast, Akbar et al. 13 reported markedly higher rates in NSTEMI patients with high TIMI risk score, with cardiogenic shock in 49.7%, cardiopulmonary oedema in 65.3% and in-hospital death in 48.5%, which is far exceeding present findings; this difference likely explained by their cohort being restricted to high-risk patients only, whereas present study included unselected NSTEMI population across risk categories.

This risk-based variation also supported by Masood et al. 14 who demonstrating that complication and mortality rate rising progressively with increasing TIMI score, from 4.4% mortality in low-risk group up to 60% in high-risk group, indicating that severity stratification is major determinant of outcome.

Regarding mortality association, present study found acute LVF and arrhythmias significantly associated with higher mortality (p=0.025 and p=0.048 respectively), which is in line with Iqbal et al. 15 who reported LVF in 34.2% and arrhythmias in 21.1% of diabetic STEMI patients, with mortality being 2.3 times higher in this group, and also with Shuja-ur-Rehman et al. 16 who showed heart failure occurring in 62% and arrhythmias in 32% of patient without ST resolution as compare to only 27% and 10% in those with resolution, supporting that persistent myocardial dysfunction and electrical instability being strongly linked with poor outcome. Cardiogenic shock, however, not reach statistical significance for mortality in present cohort (p=0.156), possibly due to small number of shock cases, though Bil et al. 17 similarly reported wide variation in arrhythmia (2–13.8%) and death rate (0.9–6.4%) across studies, reflecting heterogeneity in complication reporting.

Concerning demographic and clinical factors, present study found no significant association of age, gender, BMI, hypertension, smoking or diabetes with mortality, which is somewhat differing from Holovanova et al. 18 who identified diabetes, smoking, raised BMI and renal disease as significant predictor of early complication, while male sex and age above 70 years found protective. This discrepancy might be attributed to smaller sample size and shorter follow-up period of present study, limiting power to detect such association. Regarding invasive management, Kamble et al. 19 and Aziz et al. 20 both demonstrating that early invasive strategy reducing mortality and rehospitalisation, which support the importance of timely intervention emphasised in present study, though direct comparison of intervention timing not undertaken here. Additionally, Ahmed et al. 21 reported comparable baseline age and BMI in patient presenting atypically, with NSTEMI confirmed in 30% of cases, reinforcing that baseline demographic profile of present cohort is consistent with regional population.

However, there are some limitations associated with this research. The first limitation is that the current research has been carried out only in one center, which may affect the generalization of the results to a wider population. The second limitation is that the sample size used was rather small, especially for subgroups, such as cardiogenic shock.

Based on the findings in the current study, it can be concluded that early complications, which include cardiogenic shock, acute LVF, and arrhythmias, are very common among NSTEMI patients up to 24–48 hours following admission into the CCU. Acute LVF and arrhythmias showed a significant association with increased mortality.

1. Mohammad AM, Ali MM. Prevalence and predictors of occlusive myocardial infarction in patients presenting with non-ST-elevation acute coronary syndrome in Duhok, Iraq: a cross-sectional study. Cureus. 2024;16(7):e65299. doi: 10.7759/cureus.65299.
2. Chempay, Dorjey Y, Tshering U, Watts MR. Clinical characteristics and outcomes of acute coronary syndrome patients in a PCI-limited setting: a prospective study from Bhutan. BMC Cardiovasc Disord. 2025;25(1):324. doi: 10.1186/s12872-025-04782-w.
3. Ali F, Arshad K, Szpunar S, Daher E. Elevated troponins and diagnosis of non-ST-elevation myocardial infarction in the emergency department. Cureus. 2024;16(5):e59910. doi: 10.7759/cureus.59910.
4. Prakash GT, Dhewle P, Bose SC, Kandibendla V. Non-ST elevation myocardial infarction in patients with hypertensive emergency. Cureus. 2024;16(7):e63783. doi: 10.7759/cureus.63783.
5. Wilmé V, Harscoat S, Séverac F, Carmona A, Le Borgne P, Bilbault P, et al. Occurrence of severe arrhythmias in patients with non-ST elevation acute coronary syndrome (NSTE-ACS): a retrospective study. J Clin Med. 2023;12(10):3456. doi: 10.3390/jcm12103456.
6. Felix B, Aldoohan F, Kadirage HU, Keelathara Sajeev S, Kayani M, Hag Saeed MAI, et al. Assessment of the impact of comorbidities on outcomes in non-ST elevation myocardial infarction (NSTEMI) patients: a narrative review. Cureus. 2024;16(7):e65568. doi: 10.7759/cureus.65568.
7. Samsky MD, Morrow DA, Proudfoot AG, Hochman JS, Thiele H, Rao SV. Cardiogenic shock after acute myocardial infarction: a review. JAMA. 2021;326(18):1840-1850. doi: 10.1001/jama.2021.18323.
8. Skoda R, Bárczi G, Vágó H, Nemes A, Szabó L, Fülöp G, et al. Prognosis of the non-ST elevation myocardial infarction complicated with early ventricular fibrillation at higher age. Geroscience. 2021;43(5):2561-2571. doi: 10.1007/s11357-021-00377-3.
9. Sheng Z, Chen B. Differences in the characteristics and outcomes of STEMI versus NSTEMI cardiogenic shock: a systematic review and meta-analysis. Medicine (Baltimore). 2025;104(42):e44951. doi: 10.1097/MD.0000000000044951.
10. Díez-Villanueva P, Jiménez-Méndez C, Cepas-Guillén P, Arenas-Loriente A, Fernández-Herrero I, García-Pardo H, et al. Current management of non-ST-segment elevation acute coronary syndrome. Biomedicines. 2024;12(8):1736. doi: 10.3390/biomedicines12081736.
11. Sikandari F, Irfan G, Kubra G, Shabeen M, Qayoom R, Hassan M, et al. In-hospital outcomes of patients with non-ST elevation myocardial infarction undergoing early invasive percutaneous coronary intervention. Pak Heart J. 2024;57(3):207-212. doi: 10.47144/phj.v57i3.2776.
12. Hussain W, Younus A, Shaikh NA, Shaikh Z, Shaikh S, Hassan M, et al. Cardiogenic shock in patients with acute non ST-elevation myocardial infarction (NSTEMI). Pak Armed Forces Med J. 2021;71(6):2061-2064.
13. Akbar FE, Khan SB, Ali U. Short term clinical outcomes in non ST segment elevation myocardial infarction patients with high thrombolysis in myocardial infarction (TIMI) risk score. Pak Heart J. 2019;52(4):327-332.
14. Masood A, Naqvi MA, Jafar SS, Mufti AA, Akram Z. In-hospital outcome of acute myocardial infarction in correlation with thrombolysis in myocardial infarction risk score. J Ayub Med Coll Abbottabad. 2009;21(4):24-27.
15. Iqbal MJ, Javed MT, Tahira I. Complications and mortality in ST-segment elevation acute myocardial infarction in diabetic and non-diabetic patients. Med J Islamic World Acad Sci. 2011;19(2):87-94.
16. Shuja-ur-Rehman S, Sheikh S, Nazeer M. ST segment resolution post MI—a predictor of better outcomes. J Pak Med Assoc. 2008;58(5):283-286.
17. Bil J, Buller P, Gil RJ, Gromadziński L, Onichimowski D, Jalali R, et al. Acute complications in patients with myocardial infarction with non-obstructive coronary arteries: a systematic review with special focus on mechanical complications. Rev Cardiovasc Med. 2022;23(12):393. doi: 10.31083/j.rcm2312393.
18. Holovanova IA, Oksak GA, Tkachenko IM, Khorosh MV, Tovstiak MM, Strashko YY. Risk factors associated with the occurrence of early complications of acute myocardial infarction after cardio-intervention treatment. Wiad Lek. 2020;73(6):1245-1251. doi: 10.36740/WLek202006132.
19. Kamble A, Revunuru N, Rangachari B, Patel VB, Ullah I, Ahmed Z. Assessment of the effectiveness of early versus delayed invasive strategies in non-ST elevation myocardial infarction (NSTEMI): a systematic review and meta-analysis. Cureus. 2026;18(5):e109425. doi: 10.7759/cureus.109425.
20. Aziz EL, Morsy MA. Early versus late intervention in patients with high-risk non-ST-elevation myocardial infarction. J Med Sci Res. 2023;5(4):475-481. doi: 10.4103/jmisr.jmisr_73_22.
21. Ahmed S, Ali M, Rehman AU, Ahmed Z, Shaikh SI, Sumair F. Frequency of non-ST-elevation myocardial infarction (NSTEMI) among patients presenting with atypical presentation. Pak J Health Sci. 2023;4(5). doi: 10.54393/pjhs.v4i05.776.