a b s t r a c t

Background: ST elevation (STE) on the electrocardiogram (ECG) may be due to acute myocardial infarction (AMI) or other nonischemic pathologies such as left ventricular aneurysm (LVA). The objective of this study was to val- idate 2 previously derived ECG rules to distinguish AMI from LVA. The first rule states that if the sum of T-wave amplitudes in leads V1 to V4 divided by the sum of QRS amplitudes in leads V1 to V4 is greater than 0.22, then acute ST-segment elevation MI is predicted. The second rule states that if any 1 lead (V1-V4) has a T-wave am- plitude to QRS amplitude ratio greater than or equal to 0.36, then acute ST-segment elevation MI is predicted. Methods: This was a retrospective analysis of patients with AMI (n = 59) and LVA (n = 16) who presented with Ischemic symptoms and STE on the ECG. For each ECG, the T-wave amplitude and QRS amplitude in leads V1 to V4 were measured. These measurements were applied to the 2 ECG rules; and sensitivity, specificity, and accu- racy in predicting AMI vs LVA were calculated.

Results: For rule 1 (sum of ratios in V1-V4), sensitivity was 91.5%, specificity was 68.8%, and accuracy was 86.7% in predicting AMI. For rule 2 (maximum ratio in V1-V4), sensitivity was 91.5%, specificity was 81.3%, and accuracy was 89.3% in predicting AMI.

Conclusions: When patients present to the emergency department with ischemic symptoms and the differential diagnosis for STE on the ECG is AMI vs LVA, these 2 ECG rules may be helpful in differentiating these 2 pathologies. Both rules are highly sensitive and accurate in predicting AMI vs LVA.

(C) 2015

1. Introduction

Reperfusion therapy for ST-segment elevation myocardial infarction is indicated for patients with ischemic symptoms and ST eleva- tion (STE) on the electrocardiogram (ECG). Acute myocardial infarction (AMI), however, is not the only etiology of STE on the ECG, which can significantly complicate the clinician’s reperfusion decision. One etiolo- gy of STE that is not AMI is “persistent STE after prior MI.” This is clini- cally and pathologically manifested as left ventricular aneurysm (LVA) and is found in up to 60% of completed anterior STEMI when there is no spontaneous or therapeutic reperfusion [1]. When these patients present to the emergency department (ED) with symptoms consistent with ischemia such as chest pain or shortness of breath, this persistent STE may result in a misinterpretation of the ECG and lead to inappropri- ate reperfusion therapy [2-5].

The association between persistent STE on the ECG after prior MI and LVA has been well documented over the years, confirmed with autopsy studies [6-11] as well as echocardiography studies [12-15].

* Corresponding author. Hennepin County Medical Center, Department of Emergency Medicine, 701 Park Ave, MC 825, Minneapolis, Minnesota 55415.

E-mail address: [email protected] (L.R. Klein).

Left ventricular aneurysm is a well-known structural complication of AMI [16]. Anatomic LVA is defined as thinning and bulging of the myo- cardial wall. However, in the age of modern cardiac imaging such as echocardiography and ventriculography, the terminology LVA has come to encompass diastolic distortion, diastolic dyskinesis as well as ventricular wall akinesis, even in the absence of anatomic aneurysm [12-15,17].

The question then arises how to differentiate STE due to AMI vs STE due to LVA. Echocardiography may be used, but this is not always read- ily available in the ED, and it does not necessarily differentiate the akinesis of acute MI from prior MI and may require the use of echocar- diographic contrast for accurate diagnosis. There are several features of the ECG of LVA that can help distinguish it from AMI. These findings in- clude the presence of deep Q waves (usually QS waves), flattened T waves (often with some shallow T-wave inversion), and a lesser de- gree of STE [8,10,16,18]. None of these ECG features, however, is sensi- tive or specific for LVA.

We previously published a derivation of ECG criteria to distinguish acute anterior STEMI from anterior LVA when there is STE on the ECG [19]. This study compared multiple ECG variables, but the variable that best differentiated the 2 groups was the ratio of T-wave amplitude to QRS amplitude, exploiting the fact that there are larger T waves in acute STEMI. Based on these findings, we derived 2 “rules” using ECG measurements to differentiate STE due to AMI from STE due to LVA.

http://dx.doi.org/10.1016/j.ajem.2015.03.044

0735-6757/(C) 2015

These rules were developed based on the median T-wave amplitude to QRS amplitude ratios for each group. The first rule states that if the sum of T-wave amplitudes in leads V1 to V4 divided by the sum of QRS am- plitudes in leads V1 to V4 is greater than 0.22, then acute STEMI is pre- dicted. The second rule states that if any 1 lead (V1-V4) has a T-wave amplitude to QRS amplitude ratio greater than or equal to 0.36, then acute STEMI is predicted (Fig. 1). In the original derivation study, both of these formulas were highly sensitive and specific for predicting acute STEMI, suggesting good utility for clinicians who need to differen- tiate AMI from LVA when this is the ECG differential diagnosis. The pur- pose of the current study was to validate these 2 ECG rules in a separate cohort of patients.

1. Methods
   1. Study design

This was a retrospective cohort analysis comparing ECGs of LVA to ECGs of acute STEMI. The intent was to validate our prior derivation study, which demonstrated that the ratio of T-wave amplitude to QRS amplitude best differentiates STE in AMI from STE in LVA [19]. Approval was obtained from the institutional review board.

Study population and setting

The study was conducted in an urban ED, with an annual patient vol- ume of greater than 90000. The study cohort included consecutive ECGs of patients with LVA as diagnosed by echocardiogram. The control group included consecutive ECGs of patients with anterior STEMI and left anterior descending artery occlusion as later proven by cardi- ac catheterization. All ECGs used were those of patients who presented to the ED with ischemic symptoms such as chest pain or dyspnea.

Study protocol

To identify ECGs for the LVA group, the hospital echocardiography database was searched for the period 2002 to 2009. Using this period excluded all cases that were included in the derivation study. All echocardiography examinations in our institution are electronically coded. The code diastolic distortion aneurysm is reserved for unequivo- cal LVA. In addition, many aneurysms are coded as dyskinesis (systolic ventricular distortion). Therefore, because the presence or absence of anatomic aneurysm was not critical for the purposes of the study, we searched for all echocardiograms coded as diastolic distortion or dyskinesis. These were the same search terms used in the derivation study. Only those with anterior or apical aneurysms were included, and those with inferior or posterior aneurysms were excluded. If a pa- tient had multiple echocardiograms in the database, they were included if at least 1 of them was interpreted as diastolic distortion or dyskinesis.

Rule 2: Acute STEMI is predicted if:

Rule 1: Acute STEMI is predicted if:

Fig. 1. Two ECG rules for predicting acute STEMI vs LVA.

After these patients were identified via the echocardiography database, the electronic medical records were reviewed. The most recent ECG recorded for each patient (during an ED visit that was “not” for a STEMI) was identified. This ECG had to be from a visit that was after the echocardiographic diagnosis of diastolic distortion was made. If no such visit existed, then the patient was excluded. Further- more, after review of the electronic medical record, additional cases were excluded if (1) there were no symptoms suggestive of acute MI (chest pain, dyspnea, or arrhythmia), (2) no troponin was measured,

(3) the maximum serial troponin I was greater than 5.0 ng/mL (suggest- ing this was possibly a STEMI), (4) the patient had a coronary angio- gram at that visit showing acute or recent LAD artery occlusion, and

(5) the evaluating cardiologist retrospectively suspected acute LAD occlusion representing STEMI as the etiology of the symptoms. Any ECG that did not have at least 1 mm of STE in 2 consecutive precordial leads as measured at the J point and relative to the PR segment as well as any ECG with intraventricular conduction delay (QRS duration longer than 120 milliseconds, including any bundle branch block [BBB]) was also excluded.

For the STEMI group, the catheterization laboratory database was searched for consecutive patients with anterior STEMI presenting to the ED from October 2007 to March 2009 who underwent primary per- cutaneous coronary intervention for 100% LAD occlusion. To include a substantial number of “subtle,” nonobvious LAD occlusions, we selected 34 additional ECGs of consecutive subtle acute LAD occlusions from a cohort in a previous study [20]. In that study, ECG exclusion criteria in- cluded (1) 5 mm of STE, (2) at least 1 convex ST segment in V2 to V6,

(3) any T-wave inversion, or (4) inferior ST depressions. Exclusion criteria for both AMI cohorts included simultaneous STEMI in another distribution and those with intraventricular conduction delay (QRS du- ration longer than 120 milliseconds, including any BBB).

A rater who was blinded to the ECG group made all ECG measure- ments. The rater was not blinded to the purpose of the study. Our previ- ous study showed that intraclass coefficients were very reliable, and, therefore, only 1 rater was necessary [19]. The rater measured the QRS in millimeters, from the nadir of any Q wave, S wave, or QS wave to the peak of the R wave. The T-wave amplitude was measured, which in- cluded only the positive portion of the T wave. All measurements were relative to the PR segment and to the nearest 0.5 mm. These data were recorded from every ECG for every 1 of leads V1 to V4 and recorded di- rectly into an electronic database.

Data analysis and statistics

The data collected from each ECG was then applied to the 2 previ- ously derived ECG criteria. The ratio of T-wave amplitude to QRS ampli- tude for every lead V1 to V4 was determined. The maximum ratio in any 1 lead was recorded. The ratio of the sum of T-wave amplitudes to the sum of QRS amplitudes in V1 to V4 was determined. Statistical analysis was performed using SPSS 22.0 (2013; IBM Corp, Armonk, NY) after the completion of data collection. For the study and control groups, median ratios for both ECG rules were determined, and interquartile ranges were calculated. Sensitivity, specificity, and accuracy were determined for both rules. Comparisons were made by Mann-Whitney U test. Figs. 2 and 3 depict examples of ECGs from both cohorts and examples of measurements.

1. Results
   1. Study and control groups

There were 155 patients identified with diastolic distortion, and 16 of them met inclusion criteria. The rest were excluded due to the previ- ously stated criteria. There were a total of 59 ECGs included for the con- trol group, found to have an acute STEMI and LAD occlusion. Within the control group, there were 25 in the STEMI group and 34 in the subtle

Fig. 2. Electrocardiogram of acute STEMI successfully identified by both rules. This ECG with QS waves could easily be misinterpreted as being due to LVA or prior anterior MI. In fact, it was an acute STEMI. Measurements annotated on individual lead images (in millimeters). By rule 1, the sum of T-wave amplitudes divided by QRS amplitudes in V1 to V4 is equal to 0.29 (>=0.22 -> STEMI). By rule 2, the maximum ratio (in this ECG, V4) is equal to 0.8 (>=0.36 -> STEMI).

STEMI group. Further analysis regarding the control group going for- ward was a combination of these 2 types of STEMI.

Comparison of median ratios between study and control groups

Table 1 demonstrates the median ratios with interquartile ranges as applied to both ECG rules. The median ratios were then compared using

Mann-Whitney U test. The median ratios for the LVA group and the STEMI group were statistically different for both rules (P b .001).

Sensitivity, specificity, and accuracy of ECG rules

Table 2 shows the sensitivity, specificity, accuracy, and misclassifica- tion rate of the 2 ECG rules. Both rules were highly accurate and sensi- tive for predicting STEMI vs LVA, and rule 2 (using the maximum

Fig. 3. Electrocardiogram of LVA successfully identified by both rules. This ECG could easily be read as acute anteroseptal MI. In fact, it is the ECG of a patient with prior anterolateral MI and no acute STEMI. There are QS waves in anterior and lateral leads. Measurements are annotated on individual lead images (in millimeters). By rule 1, the sum of T-wave amplitudes divided by QRS amplitudes in V1 to V4 is equal to 0.16 (b0.22 -> LVA). By rule 2, the maximum ratio (in this ECG, V3) is equal to 0.18 (b0.36 -> LVA).

Table 1

Median calculated ratios for the STEMI cohort and LVA cohort

	Median Ratio for LVA +/- IQR	Median Ratio for STEMI +/- IQR	Comparison
Rule 1: sum V1-V4	0.203 (0.127-0.236)	0.504 (0.328-0.734)	P b .001
Rule 2: maximum ratio	0.275 (0.177-0.341)	0.800 (0.583-1.222)	P b .001

Abbreviation: IQR, interquartile range.

Comparison by Mann-Whitney U test.

ratio) was very specific as well. Table 3 depicts the accuracy, sensitivity, and specificity of the 2 ECG rules as calculated in the present validation study and in the original derivation study.

1. Discussion

When patients present to the ED with ischemic symptoms and their ECG manifests STE, it is imperative to discern STE due to AMI from STE due to nonischemic pathologies, such as LVA. In 2005, we published a derivation of 2 ECG rules for differentiating STE due to AMI from STE due to LVA. Both of these rules were based on the concept of that there are relatively larger T waves in AMI and therefore exploited the ratio of T-wave amplitude to QRS amplitude. The current study sought to validate these 2 rules within a different cohort of patients. Similar to the derivation study, we found good sensitivity, specificity, and accu- racy as well as low rates of misclassification when using these rules to predict acute STEMI vs LVA. These rules still performed well even when we included ECGs of AMI that were considered more subtle than the ECGs used in the derivation study.

Clinicians must always consider LVA as an etiology of STE on the ECG to avoid inappropriate reperfusion therapy. Unfortunately, studies have shown that LVA is a very difficult diagnosis to make on the ECG and may be the most commonly misinterpreted etiology of STE in patients pre- senting to the ED with ischemic symptoms [2,4,16,21]. Brady et al [2] showed 11 ECGs to 450 emergency physicians (EPs). The ECG of LVA was misdiagnosed as acute STEMI by 72% of EPs, a higher misclassifica- tion rate than any other ECG. The misclassification would have led to in- appropriate thrombolytic therapy by 28% of EPs. In a second study by the same authors, there were 202 ECGs with STE, and 12 ECGs were misdiagnosed–5 ECGs showed LVA, 2 of which were diagnosed as STEMI [4]. Miller et al [3] studied 100 patients admitted to a cardiac care unit for suspicion of MI. Of these patients, 31 had STE on the ECG; 21 of 21 without prior infarction and 5 of 10 “with” prior infarction had AMI. All 5 false-positive ECGs with STE were in the location of the previous Q-wave infarct (LVA), and the STE did not represent acute in- jury. In a large, more recent study, Larson et al [5] showed that 20 of 123 false Catheterization laboratory activations were due to LVA.

This frequent misclassification of the ECG of LVA demonstrates the need for specific ECG rules to differentiate STEMI from LVA. Dating back to as early as the 1950s, authors have sought to describe the ECG of LVA, but these have been descriptive studies, autopsy studies, or clinical-pathologic correlation studies, without any comparison or con- trol groups. Findings from these studies have shown that the ECG of LVA may include deep well-formed Q waves (usually QS waves), flattened T waves, T-wave inversions, a lesser degree of STE, or concave STE [8,10,16,18]. Unlike these other studies, our study, along with the origi- nal derivation article, makes direct comparisons of ECG findings be- tween cohorts of LVA and STEMI patients. It is also the first to identify the ratio of T-wave amplitude to QRS amplitude as a means to discrim- inate the 2 cohorts. To our knowledge, this is also the most accurate

Table 2

Sensitivity, specificity, accuracy, and misclassification rates for ECG rules

	Sensitivity	Specificity	Accuracy	Misclassified
Rule 1: sum V1-V4	91.5%	68.8%	86.7%	13.3%
Rule 2: maximum ratio	91.5%	81.3%	89.3%	10.7%

means of differentiating LVA from STEMI. In fact, the commonly misinterpreted ECG cited in the study of Brady et al [2] as well as other ECGs published as easily misinterpreted STEMI mimics would have been unequivocally diagnosed as LVA using our rules [22].

The success of our 2 ECG rules is based on the concept of “propor- tionality,” an idea that has received little attention in the literature. The idea of proportionality refers to the fact that the amplitude of the T wave has an expected proportion to the amplitude of the QRS. Along these lines, different proportions may suggest different pathologies. For example, it is well known that tall T waves (“hyperacute” T waves) are associated with AMI [23-25]. In our derivation study, this proportion of the T wave to the QRS was the most sensitive and specific finding that distinguished the ECG of AMI from the ECG of LVA. There were multiple other ECG measurements examined in the derivation study, but they were not as discriminatory. These included (all mea- surements from the J point as well as 60 milliseconds after the J point) degree of STE, summation of STE of V2 to V4, highest ratio of STE to QRS amplitude, and ratio of summation of STE to QRS amplitude in V2 to V4. Other measurements included height of the maximum T wave, T wave sum in V1 to V4, maximum Q wave, Q-wave sum in V2 to V4 and in V1 to V6, and absence of inverted T waves in V1 to V6 or V1 to V4. The maximum T-wave amplitude (using a cutoff of >=5 mm) and T-wave amplitude sum V1 to V4 (using a cutoff of >=11.5 mm) also had good sensitivity and specificity in differentiating AMI from LVA but did have higher rates of misclassification than the ratio rules (al- though this was not statistically significant).

Although the 2 ECG rules evaluated in this study were highly accu-

rate, there were still several ECGs that were misclassified by each rule. One hypothesis regarding the patients that were misclassified is that they had longer duration of symptoms. In acute STEMI, as the MI dura- tion increases, T-wave height diminishes [26-29]. As the T-wave ampli- tudes decreases over time, these 2 rules would be expected to be less sensitive in predicting AMI, as the ratios are now different. In the deriva- tion study, this hypothesis was evaluated. For rule 1, there were 2 of 37 AMIs that were incorrectly classified (false-negatives), and both pa- tients had greater than 6 hours of symptoms. Unfortunately, in the pres- ent study, data on the time from symptom onset to ECG were not available.

Finally, it is important to understand that the utilization of these ECG rules should be taken in their Clinical context. There are certain clinical characteristics that may help the EP determine whether the STE is due to AMI or LVA. First, patient history is essential, particularly when taken by a highly experienced clinician–active chest pain may suggest AMI, whereas dyspnea or pulmonary edema may suggest LVA (due to poor left ventricular function). A known confirmed diagnosis of LVA greatly increases the likelihood that the STE is due to LVA. Furthermore, a history of prior anterior AMI will predispose the patient to LVA, also increasing the likelihood of the STE being due to LVA, although one must be aware that a new AMI may be superimposed on an old MI. Pres- ence of Q waves alone do not necessarily suggest LVA, as QR waves may be seen within the first hour of ischemic symptoms in up to 50% of first anterior AMI [30]. However, precordial QS waves (absence of any R wave), although also present in cardiomyopathy, left ventricular hyper- trophy, and cor pulmonale, should raise suspicion of anterior LVA be- cause the Pathologic Q waves associated with LVA are characteristically QS waves in leads V2 and V3. QR waves in V2 and V3, unless in the pres- ence of a right BBB, are much less common in LVA. Lastly, ultrasound may

Table 3

Sensitivity, specificity, and accuracy for ECG rules in the derivation article and validation article

Sensitivity, derivation	Sensitivity, validation	Specificity, derivation	Specificity, validation	Accuracy, derivation	Accuracy, validation
Rule 1: sum V1-V4 95%	91.5%	91%	68.8%	93%	86.7%
Rule 2: maximum ratio 95%	91.5%	82%	81.3%	90%	89.3%

identify LVA with the presence of wall thinning or diastolic dyskinesis. A dense Wall motion abnormality may be seen in both AMI and LVA mor- phologies and therefore would not distinguish the 2 entities from one another.

1. Limitations

There are several limitations to the current study. First, the study is limited by its retrospective nature and subject to accurate coding in the echocardiographic database. Although the rater was blinded to the group from which each ECG came, the rater was not blinded to the study purpose. It is possible that LVA patients who have persistent STE after previous MI but who were not in the echocardiography database were missed. It is unlikely that patients with AMI were missed, but it is possible because data were retrospectively obtained. In review of the electronic medical records, few of the LVA patients had emergent angiography, suggesting that the suspicion for coronary occlusion was low compared with those with AMI patients (who all had emergency angiography). One must assume that the presenting characteristics of the 2 populations were sufficiently different that they underwent differ- ent management by the treating physician. Review of patient character- istics such as duration of symptoms would have been useful in the analysis of patients who were misclassified by the ECG rules. Unfortu- nately, these data were not available for certain patients; therefore, this analysis could not be conducted. Finally, the rule only differentiates patients for whom the differential diagnosis is LVA vs AMI. We do not specify prospectively precisely on whom the rule should be applied. It is implied that the ECGs to which this differential applies are those with well-formed Q waves, especially QS waves, in the anterior leads.

1. Conclusion

For patients who present to the ED with ischemic symptoms and STE on the ECG, and the ECG differential diagnosis includes STEMI vs LVA, we have derived and validated 2 rules that rely on a high T wave to QRS amplitude ratio. These 2 rules differentiate the 2 entities with good sensitivity, specificity, and accuracy. These ECG rules taken in clin- ical context may be helpful in assisting clinicians who are deciding if re- perfusion therapy is appropriate.

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