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| ORIGINAL ARTICLE |
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| Year : 2022 | Volume
: 21
| Issue : 3 | Page : 173-179 |
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The role of 12-lead electrocardiogram in the risk stratification of non-ST elevation acute coronary syndrome and the correlation with coronary angiography - The CINCHONa study - A prospective cohort study in Northern India
Barun Kumar1, Ashwin Kodliwadmath1, Amar Nath Upadhyay2, Ranjit Kumar Nath3, Neeraj Pandit3, Harsh Wardhan4, Anupam Singh5
1 Department of Cardiology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
2 Department of Cardiology, Coronation Hospital, Dehradun, Uttarakhand, India
3 Department of Cardiology, Dr. Ram Manohar Lohia Hospital, New Delhi, India
4 Department of Cardiology, Mahatma Gandhi Medical College and Hospital, Jaipur, Rajasthan, India
5 Department of Ophthalmology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
| Date of Submission | 17-Sep-2020 |
| Date of Acceptance | 07-Jul-2022 |
| Date of Web Publication | 26-Sep-2022 |
Correspondence Address:
Ashwin Kodliwadmath
Department of Cardiology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/aam.aam_85_20
 Abstract | | |
Background: Clinical guidelines recommend risk stratification of non-ST elevation acute coronary syndrome (NST-ACS) using the GRACE risk score. However, the GRACE risk score is not followed widely in clinical practice due to various reasons. Our primary objectives of this study were to correlate the presenting electrocardiogram (ECG) of NST-ACS with coronary angiography (CAG) findings and to identify specific ECG changes that are suggestive of severe coronary artery disease (CAD) thus helping to triage all patients with NST-ACS. Materials and Methods: This prospective observational study was undertaken on patients diagnosed with NST-ACS in a medical college hospital, in Northern India over one and a ½ years. The admission ECG of the patients was compared with CAG findings to find out the correlation between the two with respect to severity of CAD. Categorical and quantitative variables were compared using the Chi-square test and independent t-test, respectively. Odds ratio (OR) were calculated using the univariate logistic regression analysis. Results: On comparing the two groups with normal and abnormal ECG, we found that smokers had significantly higher odds of having an abnormal ECG (OR 3.31; 95% confidence interval [CI] [1.29–8.50]). Patients with an abnormal ECG had significantly lower left ventricular ejection fraction compared to those with normal ECG (52.01 ± 10.56 vs. 55.96 ± 6.13%, P = 0.045). The patients with severe CAD on CAG had significantly higher odds of abnormal ECG (OR 3.68, 95% CI [1.2311.04]). Of the specific ECG abnormalities, ST depression and T-wave inversion in same or different leads were significantly associated with severity of CAD (OR 0.13, 95% CI [0.04–0.43], P = 0.001 and OR 0.13, 95% CI [0.03–0.46], P = 0.002, respectively). Conclusion: The identification of ECG changes suggestive of high-risk CAD can dictate to transfer such patients without delay to a percutaneous coronary intervention capable hospital for urgent CAG with intent to revascularization, thus helping in risk stratification of NST-ACS at the community level.
| Abstract in English | | |
Résumé
Contexte: Les directives cliniques recommandent la stratification du risque de syndrome coronarien aigu sans élévation du segment ST (SCA-NST) à l'aide du GRACE cote de risque. Cependant, le score de risque GRACE n'est pas largement suivi dans la pratique clinique pour diverses raisons. Nos objectifs premiers de cette étude étaient de corréler l'électrocardiogramme (ECG) de présentation du NST-ACS avec les résultats de l'angiographie coronarienne (CAG) et de identifier les modifications spécifiques de l'ECG qui suggèrent une maladie coronarienne (CAD) sévère, aidant ainsi au triage de tous les patients atteints de NST-ACS. Matériels et Méthodes: Cette étude observationnelle prospective a été entreprise sur des patients diagnostiqués avec un NST-ACS dans une faculté de médecine. hôpital, dans le nord de l'Inde pendant un an et demi. L'ECG d'admission des patients a été comparé aux résultats du CAG pour déterminer la corrélation entre les deux par rapport à la sévérité de la coronaropathie. Les variables catégorielles et quantitatives ont été comparées à l'aide du test du Chi-carré et test t indépendant, respectivement. Les rapports de cotes (OR) ont été calculés à l'aide de l'analyse de régression logistique univariée. Résultats: En comparant les deux groupes avec un ECG normal et anormal, nous avons constaté que les fumeurs avaient une probabilité significativement plus élevée d'avoir un ECG anormal (OR 3,31 ; Intervalle de confiance à 95 % [IC] [1,29–8,50]). Les patients avec un ECG anormal avaient une fraction d'éjection ventriculaire gauche significativement inférieure à à ceux ayant un ECG normal (52,01 ± 10,56 vs 55,96 ± 6,13 %, P = 0,045). Les patients atteints de coronaropathie sévère sur CAG avaient des taux significativement plus élevés risque d'ECG anormal (OR 3,68, IC à 95 % [1,2311,04]). Parmi les anomalies spécifiques de l'ECG, le sous-décalage du segment ST et l'inversion de l'onde T dans le même ou différentes dérivations étaient significativement associées à la sévérité de la coronaropathie (OR 0,13, IC 95 % [0,04–0,43], P = 0,001 et OR 0,13, IC 95 % [0,03–0,46], P = 0,002, respectivement). Conclusion: L'identification des modifications de l'ECG suggérant une coronaropathie à haut risque peut dicter le transfert de ces patients sans délai vers un hôpital capable d'intervention coronarienne percutanée pour CAG urgent avec intention de revascularisation, contribuant ainsi au risque stratification du NST-ACS au niveau communautaire.
Mots-clés: Syndrome coronarien aigu, coronarographie, électrocardiogramme, score de risque GRACE, coronarien aigu sans sus-décalage du segment ST syndrome
Keywords: Acute coronary syndrome, coronary angiography, electrocardiogram, GRACE risk score, non ST elevation acute coronary syndrome
How to cite this article:
Kumar B, Kodliwadmath A, Upadhyay AN, Nath RK, Pandit N, Wardhan H, Singh A. The role of 12-lead electrocardiogram in the risk stratification of non-ST elevation acute coronary syndrome and the correlation with coronary angiography - The CINCHONa study - A prospective cohort study in Northern India. Ann Afr Med 2022;21:173-9 |
How to cite this URL:
Kumar B, Kodliwadmath A, Upadhyay AN, Nath RK, Pandit N, Wardhan H, Singh A. The role of 12-lead electrocardiogram in the risk stratification of non-ST elevation acute coronary syndrome and the correlation with coronary angiography - The CINCHONa study - A prospective cohort study in Northern India. Ann Afr Med [serial online] 2022 [cited 2023 Sep 22];21:173-9. Available from: https://www.annalsafrmed.org/text.asp?2022/21/3/173/356833 |
| Introduction | |  |
Acute chest pain is one of the most common reasons for referring patients to emergency department (ED). However, after diagnostic evaluation, only 15%–25% of these patients have acute coronary syndrome (ACS).[1] ACS is further classified into ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation ACS (NSTE-ACS) based on the electrocardiogram (ECG). NSTE-ACS without elevation of cardiac enzymes in the blood is called unstable angina (UA), while with the elevation of cardiac enzymes in the blood, it is called a non-ST-segment elevation myocardial infarction (NSTEMI).[2] Twelve-lead surface ECG is the 1st investigation which should be obtained within 10 min of hospital arrival or, ideally, at first contact with emergency medical services in the prehospital setting and to have it immediately interpreted by a qualified physician.[3] In contrast to evidence-based emergency provision of reperfusion therapy in STEMI,[4] the treatment pathway for NSTE-ACS is more diverse. NSTE-ACS patients are also a diverse patient group, making them more challenging to diagnose and treat. Compared with STEMI, NSTE-ACS patients tend to be older and have more comorbidity.[5] The ECG has very high specificity (97%), but very low sensitivity (28%) in ACS.[6] A clinical strategy based on high sensitivity cardiac troponin assay testing in the ED will increase the detection rate for NSTEMI, and potentially enable the earlier use of evidence-based therapies to prevent ischemic complications. Once a diagnosis of NSTE-ACS is suspected or confirmed, clinical guidelines recommend risk stratification with the GRACE score.[7] However, the GRACE risk score is not followed widely in clinical practice. The possible reasons include a lack of awareness by medical and nursing staff, a lack of access to the on-line website, and lack of time in a busy department. Many times, serum creatinine and troponin results are delayed, which further delays GRACE scoring.[5] Age is an essential component of the GRACE risk score and can have an impact on the risk stratification among patients from India as coronary artery disease (CAD) presents at a younger age in India,[8] thus questioning the sensitivity of the GRACE score for Indians. The TIMI[9] and PURSUIT[10] risk scores have also been widely validated, but GRACE has superior discriminative value for prognostication.[11] Most of the hospitals in the developing world may not have facilities for measuring troponin and creatinine required for GRACE scoring, thus relying only on ECG findings. Though ECG is a cost-effective investigation widely available in most hospitals, the interpretation requires trained personnel. In the prehospital setting, the use of telemedicine to transmit ECGs has been shown to improve time-to-reperfusion and reduce mortality for acute myocardial infarction patients.[12],[13] Hence, telemedicine can have an impact on the management strategy of NST-ACS as well.
In patients with ACS, depression of ST-segment is a frequent observation. The Crusade investigators observed that 40% of the patients had ST depression out of 55,000 population.[14] de Zwaan et al. reported T-wave inversion as a marker of left anterior descending (LAD) artery occlusion.[15] Both American and European guidelines in 2007 recommended observation of ST depression for an invasive strategy for a patient.[16],[17] However, it has been suggested that significant CAD cannot be identified with either troponin or ECG findings in NSTE-ACS.[2] Coronary angiography (CAG) is the gold standard for diagnosing CAD and its severity.
Our primary objectives of this study were to correlate the presenting ECG of NST-ACS with CAG findings and to identify the specific ECG changes that are suggestive of severe/high-risk CAD, which need urgent or emergent care by a cardiologist and thus helping to triage all patients with NST-ACS. The identification of ECG changes suggestive of high-risk CAD can dictate to transfer such patients without delay to a percutaneous coronary intervention (PCI) capable hospital for urgent CAG with intent to revascularization, thus helping in risk stratification of NST-ACS at the community level.
| Materials and Methods | | |
This prospective observational study was undertaken on patients diagnosed with NST-ACS admitted in the coronary care unit under department of cardiology in a medical college hospital, which is a PCI capable hospital in Northern India from July 2010 to December 2011.
The total sample size was 200 based on the data of admissions of NST-ACS patients to the hospital from the previous year. It was an in-hospital follow-up study and the patients were followed up for a period ranging from 2 to 12 days with an average of 6 days depending on the response to treatment and the final outcome following medical management, PCI, or coronary artery bypass graft (CABG).
The inclusion criteria were: (i) Age 18 years or more, (ii) presence of typical chest discomfort (or equivalent) believed to be ischemic in nature, lasting for at least 5 min and occurring within 96 h of (or during) hospital admission, and having an unstable pattern of pain, consisting of either rest pain, new onset, severe or frequent angina, accelerating angina or angina occurring within 21 days after an acute MI. (iii) Patient willing to undergo CAG.
The patients were excluded if (i) baseline ECG had left bundle branch block, right bundle branch block, left ventricular hypertrophy, ventricular pacing or changes of digitalis therapy, precluding the evaluation of ST segment changes, and (ii) Persistent new ST-segment elevation (except in lead aVR), or STEMI on presentation.
Ethical clearance was obtained from the Institutional Ethical Committee. The patients were included in the study if they consented to participate in the study.
At the time of admission, a complete history was taken and a meticulous physical examination was done. In the ED, a 12 lead ECG was done within 10 min of arrival and repeated if necessary. Qualitative Troponin T was done within 6–8 h of admission and if negative, was repeated after 24 h. Echocardiography was done at the time of admission or within 24 h. Left ventricular ejection fraction (LVEF) was calculated by the Simpson's method from echocardiography. Routine investigations such as complete blood count, random blood sugar on admission, blood urea, serum creatinine, and fasting lipid profile were done during the admission.
The 12-lead surface ECG was analyzed as follows:
- ST-segment depression was measured 80 milliseconds after the J point while ST-segment elevation was measured 20 milliseconds after the J-point. Preceding TP segment was used as baseline (isoelectric line)[18]
- ST-segment shift of ≥0.05 mV and T-wave inversion of >0.1 mV was considered as significant[19]
- T-wave was measured 120 milliseconds after the J point. It was considered positive if it was 1 mm or more above the isoelectric line and considered negative if it was 1 mm or more below the isoelectric line (including the normalization of a known negative T-wave)
- ECG was considered abnormal if isolated T-wave inversion of >0.1 mv (including normalization of a known negative T-wave), isolated ST-segment depression of >0.05 mv, ST-segment depression with concomitant T-wave inversion in same leads, or ST-segment depression and T-wave inversion in different leads.
The patients were divided into two groups based on ECG findings at presentation:
- Abnormal ECG
- Normal ECG.
Patients in Group 1 were further subdivided into four groups depending on the ECG findings as follows.
- Isolated T-wave inversion of >0.1 mv (including normalization of a known–ve T wave)
- Isolated ST-segment depression of >0.05 mv
- ST-segment depression with concomitant T-wave inversion in same leads
- ST-segment depression and T-wave inversion in different leads.
CAG was done in all patients according to American College of Cardiology/American Heart Association 2007 guidelines for CAG in patients of UA/NSTEMI.[16] Femoral route was used in majority of patients. A significant stenosis was defined as >50% diameter obstruction on visual analysis.
On the basis of CAG findings, patient were divided into two groups:
- Group 1: Patients having severe CAD, i.e., those having left main disease, left main equivalent disease (stenosis of proximal portion of both LAD and left circumflex coronary arteries) or severe triple vessel disease (TVD) (involving proximal or mid segment of all the three coronary arteries: LAD, left circumflex and right coronary artery [RCA]) and
- Group 2: Patients not having severe CAD, i.e., coronary artery involvement other than that of Group 1.
Patients were treated with dual anti-platelet drugs (aspirin and clopidogrel), statins, anticoagulants (unfractionated/low molecular weight heparin) beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, aldosterone antagonists, and nitrates (as indicated). Hemodynamically compromised patients were treated with normal saline or inotropes as indicated. Mechanical ventilation was used in patients with left ventricular failure with pulmonary edema if required. The patients were offered medical therapy, PCI or CABG surgery, based on the clinical scenario, CAG findings, SYNTAX score and consultation with the heart team if required.
Statistical analysis
The data are presented as frequency, percentage, mean, and standard deviation. Categorical and quantitative variables were compared using the Chi-square test and independent t-test, respectively. Odds ratio (OR) were calculated using univariate logistic regression analysis. P < 0.05 was considered statistically significant. Statistical analyses were performed using SPSS v16.0 (IBM Corp., Armonk, NY, USA).
| Results | | |
For analysis, we basically divided the patients into two groups with abnormal and normal ECG at presentation and compared the demographic variables, type of NST-ACS, risk factors, troponin T, LVEF, blood parameters, and CAG findings. Finally, we also compared the four subgroups of the abnormal ECG group patients with the severity of CAD on CAG to find out the correlation between ECG and CAG findings.
Out of 200 patients, CAG was not performed in two patients. Among these two patients, one patient expired before CAG could be done and another patient had severely deranged liver function tests, kidney function tests, low platelet count, and low Hb. Hence, these two patients were excluded from the final analysis.
Baseline characteristics and in-hospital mortality
[Table 1] presents baseline characteristics of the two groups of patients. Out of the total 200 patients (198 after excluding two patients), 167 had abnormal ECG and 31 had normal ECG at presentation. Age, sex distribution, diagnosis on admission-UA vs NSTEMI, diabetes, hypertension, and in-hospital mortality were not significantly different between both groups. Smokers had significantly higher odds of having an abnormal ECG (OR 3.31; 95% CI [1.29–8.50]).
Echocardiography and laboratory investigations
Comparison of LVEF and laboratory investigations is shown in [Table 2]. We found that patients with abnormal ECG had significantly lower LVEF compared to those with normal ECG (52.01 ± 10.56 vs. 55.96 ± 6.13%, P = 0.045). Random blood sugar on admission, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, hemoglobin, creatinine levels, and troponin positivity were comparable between both groups. | Table 2: Left ventricular ejection fraction and laboratory investigations
Click here to view |
Coronary angiography findings
[Table 3] shows the comparison of CAG findings and severity of CAD between the two groups. The patients with double vessel disease (DVD) and TVD had significantly higher odds (OR 9.0, 95% CI [2.18–37.13]) and (OR 5.69, 95% CI [1.54–20.98]) of abnormal ECG respectively. Similarly, the patients with severe CAD had significantly higher odds of abnormal ECG (OR 3.68, 95% CI [1.23–11.04]).
We also observed that LAD coronary artery was involved in 120 patients followed by left circumflex coronary artery (n = 67) and RCA (n = 67). Left main coronary artery (LMCA) was involved in 20 patients.
In this study, sensitivity and specificity of an abnormal ECG in the detection of severity of CAD were 93.7% and 20%, respectively [Figure 1]. | Figure 1: ROC curve showing sensitivity and specificity of an abnormal ECG in the detection of severity of CAD as 93.7% and 20% respectively. ROC = Reciever operating characterisctic, ECG = Electrocardiogram, CAD = Coronary artery disease
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Association between individual electrocardiogram abnormality and severity of coronary artery disease
[Table 4] shows the comparison of the four subgroups of the abnormal ECG group with the severity of CAD on CAG. We observed that ST depression and T-wave inversion in same or different leads was significantly associated with severity of CAD (OR 0.13, 95% CI [0.04–0.43], P = 0.001 and OR 0.13, 95% CI [0.03–0.46], P = 0.002, respectively). | Table 4: Association between individual electrocardiogram abnormality and severity of coronary artery disease
Click here to view |
| Discussion | | |
The current study presents the profile of 200 patients with NST-ACS and tries to correlate the presenting ECG with the severity of CAD on CAG.
We found that 84% of patients of NST-ACS presented with an abnormal ECG at presentation. Sanaani et al.[20] showed that 53% of patients of NSTEMI presented with definite ischemic ECG changes. The lower incidence of ECG changes in this study was attributed to the inclusion of patients only with elevated troponin level and patients with single vessel disease (SVD). As we included patients with both UA and NSTEMI and patients with SVD, DVD, and TVD, we found higher ECG abnormalities in our study. In addition, it has been shown that documentation of ECG during chest pain is associated with higher number of ECG abnormalities.[18] This factor can also contribute to higher rate of ECG abnormalities in our study.
We found that patients presenting with NST-ACS with normal or abnormal ECG at presentation were comparable in the mean age, sex distribution, frequency of UA and NSTEMI and prevalence of hypertension and diabetes. However, patients who were smokers were more likely to present with abnormal ECG. This was consistent with the study from Ramakrishnan et al. who showed that smoking is associated with abnormal ECG findings in male patients with acute chest pain.[21]
There was no significant difference between the two groups with respect to laboratory parameters such as LDL, HDL, random blood sugar, hemoglobin, creatinine levels, and troponin positivity. However, patients with abnormal ECG at baseline had a lower LVEF compared to those with normal ECG.
When analyzing the CAG findings of patients presenting with abnormal ECG, we found that 33% of patients had SVD, 30% patients had DVD, and 25.7% of patients had TVD. This was comaparble with the FRISCII substudy,[22] where 29% had SVD, 25% had DVD and 23.34% had TVD, respectively. We found LMCA involvement in 10.1% of cases which was comparable to 8% of cases in the FRISCII substudy.[22]
Among all the patients presenting with NST-ACS, we found that 67.2% of patients had ST segment depression (isolated or associated with T inversions in same or different leads) on the ECG, which was higher compared with other studies. In GUSTO IIb substudy,[19] 35.1% patients had ST depression while in ICTUS study,[23] 50% of the patients had ST depression. The lower rate of ST depression in the GUSTOIIb substudy was the inclusion of patients with ST elevation and exclusion of patients with normal ECG.[19] Though the rate of ST depression in the ICTUS trial was higher than that of GUSTO IIb, it was lesser than that of our study. The reason was that ICTUS study excluded patients with ST elevation, but it also excluded patients with negative troponin assays.[23] Hence, we found that among patients presenting with NST-ACS, with normal or abnormal ECG, with normal or elevated cardiac biomarkers, 67.2% of patients had ST depression on the ECG at presentation.
Further analyzing the ECG changes, we found that 33% of patients had isolated ST depression on the presenting ECG which was comparable to Savonitto et al.,[19] where 35% had ST depression. We also found that 16% patients had isolated T inversions compared to 22% in the Savonitto et al. study.[19]
Among patients presenting with abnormal ECG, 30% patients had severe CAD on CAG. Subgroup analysis of the various abnormal ECG patterns revealed that patients having ST segment depression along with T-wave inversion either in the same or other leads were found to be having severe CAD. Nikus et al.[24] showed that the ECG pattern of ST-segment depression and inverted T-waves, maximally in leads V4-5, was strongly associated with LMCA CAD, LMCA equivalent-CAD, or severe TVD. This pattern of involvement of LMCA, LMCA equivalent and severe TVD fulfils the “severe CAD” criteria used in our study. Hence, we have shown that patients having both ST depression and T inversions either in same lead or different leads are more likely to have severe TVD. This is an important finding to consider at the first medical contact be it at the community level or in the ED which can alert the treating physician to the possibility of severe CAD and urgent referral/intervention for such patients.
We also found that ECG changes were highly sensitive but less specific to predict the severity of CAD. Mahmoodzadeh et al.[25] have reported that ECG is less sensitive but more specific in the diagnosis of CAD; however, they did not report it with severity of CAD.
Limitations of the study
This was a small-scale study including only 200 participants. Larger scale studies are required to generalize the results. There was no use of intravascular imaging modalities or quantitative CAG for the diagnosis of coronary lesions, rather visual assessment of the lesions was made. This could have introduced some error in classification of the coronary lesions as severe or not severe. As per the availability, we used only qualitative troponin T for the classification of the patients into UA or NSTEMI. The use of high-sensitivity troponin quantitave assays could have shifted more patients from UA group to the NSTEMI group. The study included a short follow-up period. Long-term follow-up could indicate the long-term outcome of the patients.
Interpretation and generalisability
This study correlates the ECG changes of NST-ACS with the CAG findings for risk stratification. With the availability of the GRACE risk score for risk stratification of NST-ACS, the results of this study may get blurred, as the GRACE risk score is well validated. Due to unavailability of the creatinine and troponin tests in remote areas in India and other developing countries required for calculating GRACE score, the results of this study may still be valid and useful. Furthermore, age being an important parameter for GRACE score estimation and CAD presenting one decade earlier in Indians, the results of this study can be generalisable to the parts of Indian subcontinent, as the utility of GRACE score may be questionable, as it can underestimate the risk. Hence, the results of this study can be useful for risk stratification at the primary community level where only an ECG facility maybe available, and help to triage patients. Furthermore, as the calculation of the GRACE risk score requires time, blood investigations, software for calculation, the results of this study helping to risk stratify NST-ACS based on ECG alone may give the treating physician/cardiologist an estimate of the severity of the CAD very quickly once the ECG is taken in the ED or in the prehospital setting. However, ethnic considerations still apply and similar studies in other parts of the world, in other ethnic groups are required to generalize the results.
| Conclusion | | |
This study correlates the presenting ECG of patients with NST-ACS with CAG findings. Smokers were more likely to present with an abnormal ECG. Patients presenting with an abnormal ECG are more likely to have a lower LVEF compared to those with a normal ECG. An abnormal ECG at presentation correlates with the presence of severity of CAD as defined as LMCA, LMCA equivalent or severe TVD on CAG. Among the abnormal ECG patterns, ECG findings of ST depression and T inversions in the same or different leads predict severity of CAD on CAG. ECG changes are highly sensitive but less specific to predict the severity of CAD on CAG. Our main objective of this study was not to localize the culprit lesion on CAG by ECG but rather to identify a subset of patients with NST-ACS who have severe CAD as defined in the protocol. Thus, identification of such ECG changes can predict the presence of severe CAD which need urgent or emergent care by a cardiologist and thus helping to triage all patients with NST-ACS. Identification of ECG changes suggestive of high-risk CAD can dictate to transfer such patients without delay to a PCI capable hospital for urgent CAG with intent to revascularization, thus helping in risk stratification of NST-ACS at the community level. Larger scale studies are required to generalize the results.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4]
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