INTRODUCTION
The new criteria for acute myocardial infarction (AMI) as per the Fourth Universal Definition of myocardial infarction (MI) (2018) requires: (1) the presence of an acute myocardial injury with clinical evidence of acute myocardial ischemia; (2) detection of a rise and/or fall of cardiac troponin values with at least one value above the 99th percentile of upper reference limit; and (3) the presence of at least one of the following features – symptoms of myocardial ischemia; new ischemic changes on electrocardiogram (ECG); development of pathological Q waves; imaging evidence of new loss of viable myocardium or new regional wall motion abnormality in a pattern consistent with an ischemic etiology; or identification of a coronary thrombus by angiography or autopsy.[1
MI is categorized into ST-segment elevation myocardial infarction (STEMI) and non-STEMI based on ECG.[2 3 4 3 3 4 5 6
ECG, along with clinical presentation, is the most widely used ancillary tool for the initial assessment of patients presenting with symptoms of acute coronary s (ACS). The amplitude and/or extent of ST-segment deviation in ECG in patients with STEMI may provide valuable information about the location and extent of acute myocardial injury, which may further help optimize treatment decisions in these patients.[7 8 2 5 7 9 10 9 10 11 12 13 14 1 2 5 7
The American College of Cardiology, the American Heart Association (AHA), and the European Society of Cardiology recommend conducting a 12-lead ECG recording at the point of first medical contact with a maximum target delay of 10 min (Class 1, Level B) in patients with STEMI, along with the interpretation of the ECG by an experienced physician.[15 16 17
Various studies have analyzed the role of ECG in identifying the culprit vessel in MI, and the results have been contradictory. Rao et al . observed that ECG criteria are not the substitute of invasive procedure for differentiating the culprit artery in AMI; however, they provide an economical, reliable, and faster method of differentiating infarct-related artery in acute inferior MI.[18 et al . in their retrospective study found that in patients presenting with a suspected ACS, it is possible to identify the LAD artery and RCA as the culprit artery using ECG criteria with a reasonable degree of sensitivity (>70%) and specificity (>90%).[19 20 et al ., in their study, assessing prognostic importance of lead augmented vector right and leads V7–V9 found that lead aVR ST-deviation and lead V7 ST-deviation helped predict STEMI patients at high risk; patients with aVR ST-depression had higher mortality compared to aVR ST-elevation because of larger myocardial involvement.[21
On the other hand, few studies reported that ECG may not be able to always identify the infarct-related artery. Zhang et al . observed that coronary collateral vessels can mislead judgments of the infarct related artery by ECG. Early repolarization syndrome and anatomic variation of the coronary artery or heart or small branch occlusion can be identified as infarct by ECG.[22 et al . reported the following factors associated with failure of ECG to identify the culprit artery in patients with inferior STEMI: left coronary artery dominance, multivessel disease, and absence of ECG signs of the proximal culprit lesion.[23
Coronary angiography is another diagnostic modality, which is considered as the gold standard for identifying the infarct-related artery in STEMI. While ECG signifies the electrophysiology of the myocardium during acute ischemia, coronary angiography helps identify the vessel anatomy.[24
Considering the aforementioned literature views, the aim of this study is to describe the sensitivity and specificity of prespecified ECG criteria in localizing the culprit artery in patients with acute STEMI and to correlate the ECG findings with a coronary angiogram, thereby validating the usefulness of electrocardiography in localizing the culprit vessel in acute STEMI.
METHODS
This cross-sectional study was carried out at the Department of Cardiology, Lisie Medical Institutions, Kochi, Kerala, India. Data from the medical records of the below-mentioned eligible patients were collected from December 2017 to December 2018:
Both men and women ≥18 years of age who presented to the cardiac intensive care unit with STEMI in the last 24 h with persistent ST-elevation
Patients presenting with chest pain lasting more than 20 min, having a new ST-elevation in at least 2 contiguous leads with ST-elevation ≥2.5 mm in men <40 years, ≥2 mm in men >40 years, or ≥l5 mm in women in leads V2–V3 and/or >l mm in the other leads (in the absence of the left ventricular hypertrophy or LBBB).
Patients who were excluded included those having STEMI but did not undergo coronary angiogram and patients with LBBB in baseline ECG, paced rhythm, pericarditis, myocarditis, Brugada syndrome, stress cardiomyopathy, early repolarization syndrome, or hyperkalemia.
Patients were evaluated on the basis of clinical presentation and a 12-lead ECG at the time of admission. A detailed history of chest pain was collected along with the demographic profile (age, gender), other relevant medical history, and risk factor profile (smoking, diabetes, and hypertension). Suspected culprit vessel was identified based on the ECG changes in various leads, and patients were classified into the inferior wall myocardial infarction (IWMI) and anterior wall myocardial infarction (AWMI) categories. All patients were continuously monitored with the standard coronary care unit protocols. Once feasible, a coronary angiogram was performed. Thereafter, the suspected culprit vessel was correlated with the angiogram.
Statistical analysis
All data obtained are presented as mean ± standard deviation. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of individual ECG parameters were calculated. The ECG findings in the patients were correlated with angiogram using a measure of agreement kappa. A P < 0.05 was considered statistically significant.
RESULTS
Demographics and clinical presentation
Of the 118 patients with STEMI (92 men and 26 women), 36.4% were in the age range of 51–60 years. The mean age was 58.46 ± 10 years. A total of 86 patients presented within 6 h of chest pain. The most common risk factor was diabetes mellitus (45.8%), followed by smoking (39.8%) and hypertension (36.4%). History of exertional angina was present in 36.4% of patients. Anterior wall MI was observed in 54.2% and IWMI in 45.8% of patients. The detailed demographics and clinical characteristics are shown in Table 1 .
Table 1: Demographic and clinical characteristics
Electrocardiogram patterns for detecting occlusions in anterior wall myocardial infarction
A total of 64 patients presented with AWMI involving LAD vessel that is divided into Sl and Dl. While occlusion proximal to S1 and D1 was noted in 50% of AWMI patients, the corresponding estimates for occlusion proximal to S1 and distal to D1, distal to S1 and proximal to D1, and distal to S1 and D1 were 20.3%, 7.8%, and 21.9%, respectively. Seven patterns of ECG were considered in localizing an occlusion proximal to S1 and D1. Among these 7 patterns, the most common pattern was ST-elevation in V1, which was seen in about 76.5% of patients. Four ECG patterns were identified for occlusion proximal to S1 and distal to D1, among which the commonest one was complete right bundle branch block (RBBB) which was noted in 17.2% of patients. Four ECG patterns helped identify occlusions distal to Sl and proximal to Dl, of which ST-elevation aVL and ST-depression III > II were the most common patterns noted in 48% and 41% of patients, respectively. For detecting occlusions distal to S1 and D1, four ECG patterns were considered, of which the most common patterns noted were ST-elevation in V3-V6 and Q wave in V4–V6 in 34% and 11% of patients, respectively [Table 2 ].
Table 2: Electrocardiogram variables considered for detecting occlusion in the left anterior descending vessel
Electrocardiogram patterns for detecting occlusions in inferior wall myocardial infarction
Inferior wall MI involving RCA and left circumflex (LCx) was presented in 54 patients. While occlusions proximal and distal to RCA were noted in 44% and 26% of patients, occlusions in LCx were noted in 30% of patients. A total of eight ECG patterns were considered in localizing an occlusion proximal to RCA, and the most common patterns noted were ST-elevation ≥l mm in II, III, aVF, ST-depression 1 mm in LI, aVL (aVL > I), each in 90.7% of patients and ST-elevation in LIII > II in 74% of patients. Six ECG patterns helped detect occlusions distal to RCA. Similar to occlusion proximal to RCA, the most common patterns noted in occlusion distal to RCA were ST-elevation ≥l mm in II, III, aVF in 90.7% of patients followed by ST-elevation in LIII > II in 75.9% of patients. Seven ECG patterns were considered for identifying occlusions in LCx; S/R wave ratio aVL ≤3 followed by ST-depression in V1 is the most common patterns noted in 96.3% and 78% of patients, respectively [Table 3 ].
Table 3: Electrocardiogram variables considered for detecting occlusion in the right coronary artery and left circumflex vessels
Diagnostic value of electrocardiogram patterns for detecting occlusion in the left anterior descending artery
The sensitivity, specificity, PPV, and NPV for each of the ECG criteria for detecting occlusion in LAD artery proximal to S1 and D1, proximal to S1 and distal to D1, distal to S1 and proximal to D1, and distal to S1 and D1 are shown in Table 4a ,b ,c ,d .
Table 4a: Diagnostic value of electrocardiogram patterns for detecting occlusion proximal to S1 and D1 in the left anterior descending artery
Table 4b: Diagnostic value of electrocardiogram patterns for detecting occlusion proximal to S1 and distal to D1 in the left anterior descending artery
Table 4c: Diagnostic value of electrocardiogram patterns for detecting occlusion distal to S1 and proximal to D1 in the left anterior descending artery
Table 4d: Diagnostic value of electrocardiogram patterns for detecting occlusion distal to S1 and D1 in the left anterior descending artery
Proximal to S1 and D1
For the detection of occlusion proximal to S1 and D1 in LAD artery, while ST-elevation ≥2.5 mm in Vl had the highest sensitivity (90.6%) followed by ST-elevation in aVL, V1 (87.5%) and ST-depression ≥1 mm II, III, aVF (78%), ST-depression in V5 had 100% specificity, followed by ST-elevation aVR and complete RBBB, which had 97% and 90.6% specificities, respectively [Table 4a ].
Proximal to S1 and distal to D1
ST-elevation in aVL and complete RBBB had 31% sensitivity and 15.4% sensitivity, respectively, for the detection of occlusion proximal to S1 and distal to D1. The corresponding specificities were 96% and 82%, respectively; ST-elevation in aVR and ST-depression in V5 also had a high sensitivity of 90% [Table 4b ].
Distal to S1 and proximal to D1
While ST-depression in III >II had maximum sensitivity (100%) followed by ST-elevation in aVL (80%), Q wave in V4–V6 and Q wave in augmented Vector Left (a VL) had 83% and 56% specificity, respectively, for detecting occlusion distal to S1 and proximal to D1 [Table 4c ].
Distal to S1 and D1
Only ST-elevation in V3–V6 had a high sensitivity of 78.6%, followed by ST-elevation in II, III, aVF (28.6%), ST-depression in aVL (21%) and Q wave in V4–V6 (21%) for detecting occlusion distal to S1 and D1. The corresponding specificities were 54%, 94%, 90%, and 84%, respectively.
Diagnostic value of electrocardiogram patterns for detecting occlusion in right coronary artery
Proximal to right coronary artery
While both ST-elevation ≥1 mm in II, III, aVF, and ST-elevation in LIII > II had maximum sensitivity of 100% followed by ST-depression > 1 mm in L1, aVL (96%) and RV4-T wave upright (83%), ST-elevation in V1, S/R wave ratio of aVL > 3, and ST-elevation ≥ 1 mm in V4R had specificity of 97%, 93%, and 77%, respectively [Table 5a ].
Table 5a: Diagnostic value of electrocardiogram patterns for detecting occlusion in proximal right coronary artery
Distal to right coronary artery
Similar to occlusion in the proximal segment, ST-elevation ≥1 mm in II, III, aVF and ST-elevation in LIII >II had 100% sensitivity followed by ST-coving without ST-elevation in RV4 (78.5%). S/R wave ratio of aVL >3 had maximum specificity (100%) followed by ST-depression V3/ST-elevation LIII 0.5–1.2 (82.5%) and ST-coving without ST-elevation in RV4 (70%) [Table 5b ].
Table 5b: Diagnostic value of electrocardiogram patterns for detecting occlusion in distal right coronary artery
Diagnostic value of electrocardiogram patterns for detecting occlusion in the left circumflex artery
While S/R wave ratio of aVL ≤ 3 and ST-depression ≥0.5 mm in V1–V3 had 100% sensitivity followed by ST-elevation ≥0.5 mm in V7–V9 (94%), ST-elevation in LII >III and isoelectric or ST-elevation in L1 and aVL had 100% specificity followed by ST-depression in V3/ST-elevation in LIII >1.2 (95%) and RV4 inverted T wave (89.5%). The corresponding PPV, NPV, and accuracy values are shown in Table 6 .
Table 6: Diagnostic value of electrocardiogram patterns for detecting occlusion in the left circumflex
Correlation between electrocardiogram and coronary angiogram for detecting occlusion in the left anterior descending artery
For detecting occlusion proximal to S1 and D1, ST-elevation in aVL and Vl had the maximum and a statistically significant correlation (κ = 0.531; P = 0.000) followed by ST-depression ≥1 mm II, III, aVF (κ = 0.375; P = 0.002), while complete RBBB has the least correlation (κ = 0.156; P = 0.098) with the coronary angiogram [Table 7a ].
Table 7a: Correlation of electrocardiogram with angiogram for detectingocclusion proximal to S1 and D1
For detecting occlusion proximal to S1 and distal to D1, the maximum correlation was observed with ST-depression in aVL (κ = 0.336; P = 0.003) and the least correlation with ST-depression in V5 (κ = −0.127; P = 0.240) [Table 7b ]. None of the ECG patterns for detecting occlusion distal to S1 and proximal to D1 had a significant correlation with angiogram. For detecting occlusion distal to S1 and D1, the maximum correlation was observed with ST-elevation in II, III, aVF (κ = 0.275; P = 0.017) and least correlation with Q wave in V4–V6 (κ = 0.059; P = 0.634) [Table 7c and d ].
Table 7b: Correlation of electrocardiogram with angiogram for detecting occlusion proximal to S1 and distal to D1
Table 7c: Correlation of electrocardiogram with angiogram for detecting occlusion distal to S1 and proximal to D1
Table 7d: Correlation of electrocardiogram with angiogram for detecting occlusion distal to S1 and D1
Correlation between electrocardiogram and coronary angiogram for detecting occlusion in the proximal right coronary artery
While the maximum correlation was observed with ST-elevation in LIII > II (κ = 0.438; P = 0.000), followed by V4R-T wave upright (κ = 0.386; P = 0.003) and ST-elevation ≥1 mm V4R (κ = 0.354; P = 0.009), least correlation was observed with ST-elevation ≥0.5 mm V7–V9 (κ = −0.382; P = 0.005) and ST-depression ≥0.5 mm V1–V3 (κ = −0.379; P = 0.004) [Table 8a ].
Table 8a: Correlation of electrocardiogram with angiogram in detecting occlusion in proximal right coronary artery
Correlation between electrocardiogram and coronary angiogram for detecting occlusion in the distal right coronary artery
The maximum correlation was observed with ST-coving without ST-elevation in RV4 (κ = 0.402; P = 0.002). The least correlation was observed with ST-elevation ≥0.5 mm V7–V9 (κ = −0.191; P = 0.122) [Table 8b ].
Table 8b: Correlation of electrocardiogram with angiogram in detecting occlusion in distal right coronary artery
Correlation between electrocardiogram and coronary angiogram for detecting occlusion in the left circumflex artery
While isoelectric or ST-elevation in L1 and aVL (κ = 0.580) followed by ST-depression in V1 (κ = 0.523), RV4 inverted T wave (κ = 0.502) and ST-elevation in LII ≥III (κ = 0.449) had maximum correlation, all statistically significant (P = 0.000), ST-depression ≥0.5 mm in V1–V3 (κ = 0.032; P = 0.350) and S/R wave ratio of aVL ≤3 (κ = 0.094; P = 0.256) had least correlation [Table 9 ].
Table 9: Correlation of electrocardiogram with angiogram in detecting occlusion in left circumflex
DISCUSSION
In the present cross-sectional study, we successfully determined various ECG criteria for the diagnosis of the infarct-related artery and prediction of the site of occlusion in patients with STEMI and correlated the results with angiographic findings. Further, we have calculated Cohen's kappa (k) along with the estimation of validity, which predicted a fair to substantial agreement between ECG and coronary angiogram for localizing the culprit artery in STEMI patients with reliable correlation.
The incidence of CAD in our study was four times higher in males (78%) than in females (22%). Similar gender distribution was found in the study by Rao et al . (73% males and 27% females) and Bhat et al . (82% males and 18% females).[18 25 26 27 28
Among the risk factors documented in our study, diabetes mellitus was found to be most common, accounting for 45.8% followed by smoking in 39.8%, hypertension in 36.4%, and dyslipidemia in 24.6%. The INTERHEART-South Asia study identified eight coronary risk factors: abnormal lipids, smoking, hypertension, diabetes, abdominal obesity, psychosocial factors, low fruit and vegetable consumption, and lack of physical activity, which accounted for 89% of all acute MI cases in Indians.[5 27 et al .[29 30 31 32 33
Among the 118 patients included in our study, 54% of patients had AWMI in the LAD artery, and 46% of patients had IWMI involving RCA and LCx artery. Further, most of the population had occlusion proximal to S1 and D1 in the LAD artery (50%). This distribution is similar to the distribution reported by Rao et al. Out of 126 patients in the focus study, 55% of patients had AWMI involving the LAD artery with more than 50% detected with occlusion proximal to S1 and D1.[18 et al. reported 52% of patients with occlusion in LAD artery and 48% in the RCA artery.[34
The American Heart Association, American College of Cardiology Foundation (ACCF), and the Heart Rhythm Society (HRS) recommendations for the standardization and interpretation of ECG have outlined specific ECG criteria for detecting occlusions in the LAD artery. These include: (1) when ST-elevation is in leads I and aVL, as well as in leads V1–V4 and sometimes in V6, and ST-depression is in leads II, III, and aVF, the automated interpretation should suggest an extensive AWMI due to occlusion of the proximal portion of the LAD; (2) when ST-elevation is in leads V3-V6 and ST-depression is not in leads II, III, and aVF, the automated interpretation should suggest AWMI due to the occlusion of the mid or distal portion of the LAD.[35
In our study, patients with AWMI, different ECG criteria were used to identify the culprit artery. Seven criteria were used for localizing the culprit vessel proximal to S1 and D1; ST-elevation ≥2.5 mm in Vl was the most sensitive (90.63%), while ST-depression in V5 was associated with maximum specificity. These results are consistent with the study by Salunke and Khyalappa in which maximum sensitivity and specificity were noted with ST-elevation ≥2.5 mm in Vl and ST-depression in V5, respectively. Further, the specificity of >90% for complete RBBB noted in our study was also in line with the observation by Salunke and Khyalappa.[8 et al ., ST-elevation in lead aVR, complete RBBB, ST-depression in lead V5 and ST-elevation in Vl l2.5 mm strongly predict LAD occlusion proximal to Sl.[36 P < 0.001), suggesting moderate agreement between ECG and coronary angiogram.
Of the four criteria used in detecting occlusion proximal to S1 and distal to D1, ST-depression in aVL had high specificity and low sensitivity which is in line with the findings by Bhat et al . However, high sensitivity and low specificity in ST-elevation in leads V1–V4 in our study were contrary to the moderate sensitivity and high specificity noted by Bhat et al. [37 P = 0.003), indicating a fair agreement between ECG and coronary angiogram. However, we could not find any studies reporting similar correlation in the literature.
In detecting occlusion distal to S1 and proximal to D1, while maximum sensitivity was noted with ST-depression in III > II, high specificity was noted with Q wave in leads V4–V6. However, the Cohens kappa was found to be low in all the ECG patterns, indicating a poor association with the angiogram. The proportion of patients having this type of occlusion is very less in the current study, which might explain the poor validation of the ECG.
In our study, the presence of Q waves in leads V4–V6 had high specificity for detecting occlusion distal to S1, and ST-depression in lead aVL has high specificity for detecting occlusion distal to D1. The measure of agreement kappa was 0.27 and 0.2l, both P < 0.05 for ST-elevation in inferior leads and ST-elevation in V3–V6, respectively, implying a fair agreement with the angiogram. In line with our study, Engelen et al. also reported that ST-depression in aVL and Q wave in leads V4–V6 was highly specific in predicting an occlusion distal to D1.[36
According to the AHA/ACCF/HRS recommendations, IWMI that results in ST-elevation in only leads II, III, and aVF may be the result of occlusion of either the RCA or the LCx. Greater ST-elevation in lead III as compared to lead II is often associated with RCA occlusion. Further, lead V4R is of great value in diagnosing right ventricular involvement in the setting of an inferior wall infarction and in making the distinction between RCA and LCx occlusion and between proximal and distal RCA occlusion.[35
In the current study, ST-elevation >l mm in leads II, III, and aVF and ST-elevation in III >II were the most common variables used for detecting an occlusion in proximal and distal RCA. Both these patterns were 100% sensitive in our study. Similarly, Salunke and Khyalappa and Gaude et al . noted ST-elevation III >II was 100% sensitive in diagnosing occlusions in the RCA.[8 38 et al. [7 8 18
The AHA/ACCF/HRS guidelines state that occlusion in LCx is associated with ST-depression in leads V1, V2, and V3 or ST-elevation in lead II >III and maybe isoelectric or ST-elevation in leads 1 and aVL.[35 et al . reported 96% of specificity for these ECG patterns in predicting LCx occlusion.[8 18 21 39 P < 0.05. However, literature is sparse to support this finding.
Limitations
The study has few limitations which include a single-center, observational study design with small sample size. Most of the patients who presented to our coronary care unit with angina and persistent ST-elevation had a late presentation of up to 24 h. Since they were included in the study, we have missed the early evolution of ECG patterns.
CONCLUSION
The present study demonstrates that ECG is valuable not only for determining early reperfusion therapy but also for providing information regarding the location and extent of acute myocardial injury in patients with STEMI prior to angiography. In AWMI, ECG is more reliable for detecting occlusion proximal to S1 and D1 and in IWMI it can be reliably used in detecting occlusions either in RCA or LCx. Further, the ECG patterns in the proximal coronary artery occlusion reflect relatively large MIs that will benefit with early and complete revascularization strategies such as angioplasty.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
ACKNOWLEDGMENTS
We would like to thank BioQuest Solutions Pvt Ltd., for data management, analysis, and providing editorial services.
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