Correlation and Prognostic Signicance of Electrocardiography, Echocardiography and Troponin in Patients Admitted with NSTEMI

Background: Non ST segment elevation myocardial infarction (NSTEMI) is a clinical condition characterized by typical symptoms of myocardial ischemia along with electrocardiographic changes and a positive value of troponin. After presentation in emergency department these patients have their troponin I value and electrocardiography done. The echocardiography should also be performed in these patients. This study was conducted to determine the relationship between ECG, Echo and troponin and how prognostically these are relevant to each other along with their prognostic signicance. Results: This observational study was conducted at tertiary care cardiac hospital on 221 patients diagnosed with the NSTEMI. The most frequent nding on presenting ECG was ST depression in anterior leads (V1-V6) in 27.6%. Median troponin I at presentation was 3.2 ng/dl and median ejection fraction was 45%. Overall all-cause mortality rate at 6-months was observed to be 8.6%, re-infarction in 5%, re-hospitalization in 16.3%, and heart failure in 25.3% was observed. However, mortality was higher for patients with baseline ECG ndings of A-b, generalized ST-depression , poor R-wave progression, Wellens sign, and T-wave inversion in inferior also mortality rate was relatively higher among patients with poor (<30%) LVEF. Conclusion: ECG and Echocardiography were prognostically signicant and correlated better at 6 months. However Troponin lacks the association and prognostic signicance at 6 months.


Background
Non ST-segment elevation myocardial infarction (NSTEMI) is a clinical condition characterized by typical symptoms of myocardial ischemia along with electrocardiographic changes and a positive value of troponin. After presentation in emergency department these patients have their troponin I value and electrocardiography done [1], echocardiography should also be considered in these patients. Furthermore, these investigations are helpful in risk strati cation and for further decision making to undergo coronary intervention or to manage conservatively.
Although all these modalities have high impact on prognosis independently. However, there are no studies available which correlated altogether the ECG, Echo and Troponin. Moreover, admitting ECG ndings are valuable in the assessment of risk and predict the prognosis in patients with NSTEMI [2,3]. ECG could have numerous ndings including ST segment depression, T wave inversion and most of the time ECG could be normal or have nonspeci c ndings. Previous studies have shown that ST depression have adverse short term and long term cardiovascular outcomes [4,5]. Additionally, Troponin is a biomarker which is preferable in the setting of acute coronary syndrome and differentiates from unstable angina. Although, management strategy is same for both the conditions and there are multiple studies on the prognostic value of troponin in NSTEMI [6][7][8][9][10][11]. Subsequently, Echocardiography is the basic tool to further evaluate the patients with NSTEMI to recognize segmental wall motion abnormalities [12,13]. And left ventricular ejection fraction along with other parameters. This would be helpful in deciding the further management plan.
Therefore, studies like this which could associate all the basic modalities in NSTEMI and jointly signify the outcome in these patients is needed for further risk strati cation.
This study was conducted to determine the relationship between ECG, Echo and troponin and how prognostically these are relevant to each other along with their prognostic signi cance. Such information would help physicians to categorize the patients further with their management plan.

Methods
This observational study was conducted at the tertiary care cardiac hospital of Pakistan from august 2019 to august 2020. The sample size of this study was calculated by using the standard online equation and this was approximated to be around 300 patients. All the patients diagnosed with NSTEMI were enrolled in this study. The patients who were not diagnosed with NSTEMI and who did not give consent were excluded from this study. Electrocardiography, troponin was the basic tool along with echocardiography.
This study was commenced after the approval of ethical review committee of the hospital. Oral consent was taken and documented from all the enrolled patients. Baseline features including age, gender, risk factors such as diabetes, hypertension, obesity, smoking, and family history of premature coronary artery disease were documented on the designed questionnaire along with the vitals of the patients.
Electrocardiography was performed to see any particular ischemic ndings and troponin value was also categorized. On echocardiography, left ventricular ejection fraction was divided into two categories of LVEF < 40%, and LVEF > 40%. These all ndings were noted to correlate with each other and to determine the outcome. All the patients were followed up to 6 months and outcomes such as all-cause mortality, reinfarction, re-hospitalization, and heart failure were recorded.
Data analysis was performed with the help of IBM SPSS version 21, descriptive summary such as mean ± SD, median [interquartile range (IQR)], and range (maximum -minimum) were calculated for continuous variables and frequency and percentages were calculated for categorical variables.

Results:
A total of 221 patients with NSTEMI were included, out of which 76.9% (170) were male and mean age was 57.63 ± 10.48 years with 20.4% (45) above 60 years of age. A majority (84.6%) of patients were in killip class I at presentation and only 2.7% (6) patients were in killip class III and no patients was in killip class IV. The commonest co-morbid condition was hypertension (82.4%) followed by diabetes (41.6%) and smoking (26.2%). Sedentary lifestyle was reported by 24.9% (55) of the patients. The most frequent nding on presentation ECG was ST depression -anterior (27.6%) followed by T wave inversion -anterior (14%), 12.2% (27) patient had non-speci c changes, and 16.3% (36) patients had normal ECG.
Median troponin I at presentation was 3.  Table 1.
Distribution of troponin I by various ECG changes are presented in Figure 1. Proportion of patients in 4 th quartile (>7.30 ng/dL) was more prominent for the patients with baseline ECG ndings of poor R-wave, ST depression -generalized, and ST-depression inferior, while, lower quartile distribution of troponin I was more commonly observed with non-speci c ECG changes, normal ECG, T-wave inversion -inferior, ST-depression lateral, and ST-depression -anterior.
Distribution of ejection fraction by various ECG changes are presented in Figure 2. Poor LVEF (%) can be seen with ECG nding of A b, poor R-wave, ST-depression -anterior, and ST-depression inferior. LEVF was in normal range for most of the patients with normal ECG and ST-depression -lateral.
Correlation between troponin I and left ventricular ejection fraction against various ECG changes are presented in Figure 3. High troponin I levels and low LVEF was found to be related with ECG changes of ST-depression -generalized, poor R-wave, and A b. While, low troponin I levels and high LVEF were observed against ECG changes of ST-depression -lateral, T-wave inversion -anterior, -inferior, andlateral, Wellens sign, and normal ECG.
Adverse cardiac event rate at 6-months for various ECG changes, troponin I quartiles, and ejection fraction categories are presented in Table 2. Overall all-cause mortality rate at 6-months was observed to be 8.6%, re-infarction rate of 5%, re-hospitalization in 16.3%, and heart failure rate of 25.3% was observed.
All-cause mortality rate was relatively higher for patients with baseline ECG ndings of A b, STdepression -generalized, poor R-wave, Wellens sign, and T-wave inversion -inferior also mortality rate was relatively higher among patients with poor (<30%) LVEF. The relationship between mortality rate and troponin I level is non-conclusive.
Re-infarction rate was also relatively higher for the patients with ECG ndings of A b, Wellens sign, and ST-depression generalized. Re-infarction rates are surprisingly tends to remain higher for lower quartile of troponin I. Poor LVEF was also observed to be associated with higher re-infarction rate. Heart failure rate was observed to be related to poor LVEF and baseline ECG ndings of A b, ST-depression -generalized, poor R-wave, T-wave inversion inferior. However, relationship of troponin I and heart failure rate remain inconclusive.

Discussion
The current study shows one of the biggest and recent evaluation of patients with NSTEMI in the cotemporary era according to the presentation of ECG ndings along with Troponin level and echocardiography from a large tertiary care center of Pakistan. The most signi cant nding on ECG in the present study was ST depression and T wave inversions in anterior leads that collectively accounted for 41.6% (ST depression anterior 27.6%, anterior T wave inversion 14 %) of total patients diagnosed with NSTEMI. This was in contrast from one of the large study by Patel et  This study revealed the signi cance of low ejection fraction < 30% resulted in overall mortality of 35% in comparison to the EF of 30-45 and > 45% had 9.6% and 1.2% respectively. There is no such study which linked ejection fraction and other echo parameters with outcomes including mortality in NSTEMI patients. Heart failure and re-infarction was also found to be signi cant with low EF of 60% and 25% respectively.
ECG, Echo and troponin altogether categorize the patients according to associated risk and will be detrimental in making a management plan and helpful for clinicians in decision making.
This study has few Limitations as this was the single center study and smaller volume of sample that could not be generalized. Therefore, a multicenter large volume study is required to generalize to the whole population.

Conclusion
Electrocardiography along with echocardiography has a better prognostic signi cance at 6 months. However, troponin considered as of high importance could not associate with ECG and Echo in terms of predictive value. Furthermore, ECG and ECHO are correlated with each other in patients with NSTEMI.