Electrocardiographic identification of the infarct-related artery in acute inferior myocardial infarction

Inrern~tional

Journal

of

cardiology ELSEVIER

InternationalJournalof Cardiology54 (1996)5-11

Electrocardiographic identification of the infarct-related artery in acute inferior myocardial infarction Cheuk-Kit Wang”, S. Ben Freedman The Hallstrom Institute of Cardiology,

University of Sydney, Royal Prince Alfred Hospital, Sydney, Australia

Received2 August 1995;accepted23 January1996

Abstract Differentiation between left circumflex occlusion and right coronary occlusion in inferior acute myocardial infarction is a common clinical problem. This study investigated new electrocardiographicmarkersfor differentiation, including T wave inversion, and individual inferior and precordial lead ST level, versus the traditional criterion of lateral ST elevation. In 95 angiographically characterisedpatients, ST elevation in lateral chest lead V5 or V6 had a sensitivity of 56% and specificity of 92% to predict left circumflex related acute myocardial infarction while the absenceof lateral T inversion in I and AVL was even more sensitive (89%) though less specific (74%). A criterion of ST depressionin Vl > 0.1 mV has a sensitivity of 61% and specificity of 84% whereas a criterion of ST level in III minus II 5 0.1 mV has a sensitivity of 94% and specificity of 37% in predicting left circumflex related acute myocardial infarction. These criteria were then tested in another 49 patients subsequently recruited with inferior acute myocardial infarction. Useful parametersthat discriminated left circumflex related acute myocardial infarction from right coronary related acute myocardial infarction include lateral ST elevation (38% vs. 7%, P < 0.05), absenceof lateral T inversion (50% vs. 15%, P < 0.05), and ST depressionin Vl of more than 0.1 mV (50% vs. 7%, P < 0.05). The present study revealed new electrocardiographic clues to suggesta left circumflex related inferior acute myocardial infarction other than lateral ST elevation. However, it should be noted that no single electrocardiographicvariable or their combinations could identify the infarct-related artery with complete certainty. Keywords:

Infarct-related artery; Inferior infarction

1. Introduction In the era of thrombolysis, ST monitoring methods have been used to diagnose success or failure

*Corresponding author.Presentaddress:Department of Meditine, University of Hong Kong, QueenMary Hospital,Hong Kong. Fax: +852 28551143.

of thrombolytic therapy in acute myocardial infarction [1,2], and coronary angioplasty, either as a primary therapy or a rescue procedure has become an established treatment modality [3,4]. Physicians may accurately identify the infarct-related left anterior descending artery in anterior acute myocardial infarction. However, the differentiation between right coronary versus left circumflex occlusion in inferior acute myocardial infarction is more

0167-5273/96/$15.00 0 1996ElsevierScienceIrelandLtd. All rights reserved PII SO167-5273(96)02581-8

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C.K. Wong, S.B. Freedman I International

difficult. Previous studies have used ST changesin different lead groups to addressthis problem [5,6]. Lateral ST elevation was considered almost diagnostic of left circumflex related acute myocardial infarction in a previous study [5]. Conversely, T wave changes in inferior acute myocardial infarction have seldom been studied [7], and individual lead ST change within each lead group has not been fully explored. From the perfusion distribution of the circumflex artery versus the right coronary artery [8], lateral and posterior infarction occurred more commonly with circumflex occlusion and right ventricular infarction with right coronary occlusion. Lead II and III have a different relative orientation towards the lateral myocardium, and precordial lead Vl and V3 have a different relative orientation towards the right ventricle and posterior left ventricle. We compared the ST levels in II versus III, and in Vl versusV3 to discern whether the changes can differentiate between right coronary and left circumflex occlusions. We also examined the relative role of these new electrocardiographic parametersincluding T wave changes in discriminating the infarct-related artery in inferior acute myocardial infarction, as compared to lateral ST elevation.

2. Materials

and methods

2.1. Patients

Two groups of patients were used. An original group with 77 right coronary related inferior acute myocardial infarction and 18 with left circumflex related inferior acute myocardial infarction were included as‘previously reported [9, lo]. The electrocardiographic parametersgeneratedwere then tested in the next group of 49 patients recruited subsequentlybetween January 1991 and June 1994. All patients had first episode inferior acute myocardial infarction (defined as 20.1 mV ST elevation in ~2 inferior leads) without other concomitant organic heart disease,bundle branch block, preexcitation, or ventricular hypertrophy with strain pattern. Angiography was performed within 3 months of the

Journal of Cardiology 54 (1996) 5-11

first presentation. Patients with concomitant anterior ST elevation were excluded. 2.2. Electrocardiographic

evaluation

All initial electrocardiographs of each patient were reviewed and the electrocardiograph which showed acute inferior infarct pattern with the greatestmagnitude of ST elevation was selectedfor analysis. ST elevation or depression was measured at 60 ms after the J point. Four electrocardiographic lead groups: inferior limb leads (II,III,AVF), precordial leads (Vl-3), lateral chest leads (V5-6) and lateral limb leads (1,AVL) were defined [ll]. Significant T inversion was defined to be present if the nadir of the T wave measured20.2 mV below the isoelectric TP segment [7]. 2.3. Angiographic

evaluation

All coronary angiograms were reviewed by two angiographers blinded to other dam. Stenoses > 50% were considered significant. The infarct-related lesion was identified based on morphology including total obstruction, thrombus and ulcerative stenosis, or assumedto be the tightest stenosis if these features were absent. In the original 95 patients, none had concomitant right coronary artery and left circumflex artery disease [9], In the subsequent49 patients, patients with concomitant diseaseof the right coronary artery and left circumflex artery were not excluded provided that the infarct-related lesion could be clearly identified. Concomitant left anterior descending disease was present in 30 of the original 95 patients and 27 of subsequent 49 patients. None had significant left main disease. 2.4. Statistical analysis

Where appropriate, chi square test and Fisher exact test, unpaired t-test and paired t-test were used to examine differences between groups. Multiple logistic regression analysis was performed to identify the independentpredictor of left circumflex related acute myocardial infarction. P-values (2-

C.K. Wang, S.B. Freedman I International

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54 (1996) 5-11

7

tailed) < 0.05 were considered significant. Results are expressedas mean + standard deviation.

74%) than in left circumflex related infarction (two of 18 patients, ll%, P < 0.001).

3. Results

3.2. Inferior ST elevation in right coronary versus left circumfex related inferior acute myocardial infarction (Table 2)

3.1. ST and T changes in right coronary versus circumJex related inferior acute myocardial infarction (Table 1)

left

Within group paired comparison showed that ST level in lead III was statistically higher than that in lead II (P < 0.001) in right coronary related infarction (Table 2). This was not the case for left circumflex related infarction. Indeed, the difference of ST levels between leads II and III was larger in right coronary group. Twenty-one of the 77 patients (27%) with right coronary related infarction versus one of the 18 patients (6%) with left circumflex related infarction (P < 0.01) had more than 0.1 mV ST segment elevation in lead III than in lead II (Table 2).

The number of leads showing ST elevation was greater in left circumflex related infarction due to the presence of ST elevation in lateral chest leads V5,6. Summed inferior ST elevation and summed precordial ST depression were not different between the two groups. Similarly, there was no difference in T inversion over the chest leadsVl-6 between the two groups. In contrast, T inversion in lateral limb leads I and AVL was more common in right coronary related infarction (57 of 77 patients,

Table 1 Comparison of ST and T changesin right coronary versus left circumflex related acute myocardial infarction RCA related infarct Number of patients ST change No. of leads with ST? No. of leads with STJ Patients showing STT in leads VS or V6 Patients showing ST? in leads I or AVL

LCX related infarct 18

77

2.9 -c 0.7 3.7 2 2.1 6 0

ST levels .ZII,III,AVF (mV) HVl-3 (mV) z‘V.5,6 (mV) BI,AVL (mV)

0.77 -0.38 -0.05 -0.29

T inversion (TJ) No. of leads with TJ No. of Vl-6 leads with TJ Patientsshowing TJ in leadsVl or V2 or V3 Patients showing TL in leads V5 or V6 Patients showing T& in leads I or AVL

1.82 ? 1.66 0.97 ? 1.44 31 5 57

2 k ? t

0.47 0.49 0.14 0.07

3.9 -c 1.0*** 3.9 2 2.6 lo*** 1* 0.71 t 0.37 -0.61 k 0.58 0.16 t 0.28*** -0.16 _’ 0.16**

1.39 k 1.29 1.28 t 1.27 11 0

2***

Significant ST segment change was defined as 20.1 mV elevation or depression,measuredat 60 ms after the J point. Significant T inversion was defined to be present if the nadir of the T wave measured SO.2 mV below the isoelectric TP segment; LCX, left circumflex artery; RCA, right coronary artery. *P < 0.05. **p < 0.01. ***p < 0.001.

8

C.K. Wong, S.B. Freedman I International

Journal of Cardiology 54 (1996) 5-11

Table 2 Individual inferior and precordial lead ST level in differentiation of right coronary versus left circumflex related inferior acute myocardial infarction RCA related infarct

LCX related infarct

P-value

Inferior ST elevation ST level in Il (mV) ST level in III (mV) P-value of paired comparison of ST level in III and II ST level in III minus ST level in II (mV) proportion of patients with ST level in (III minus II) > 0.1 mV

0.21 2 0.15 0.31 ? 0.17
0.24 t 0.12 0.25 t 0.14 NS 0.01 t 0.08 1118

NS NS

Precordial ST depression ST level in Vl (mV) ST level in V3 (mV) P-value of paired comparison of ST level in Vl and V3 ST level in V3 minus ST level in Vl (mV) proportion of patients with ST depressionin Vl > 0.1 mV

-0.05 5 0.11 -0.14 +- 0.21
-0.15 * 0.10 -0.22 t 0.25 NS -0.07 2 0.21 11/18

0.001 NS


NS 0.001

ST levels were measuredat 60 ms after the J point; LCX, left circumflex artery; RCA, right coronary artery.

significant for right coronary related acute myocardial infarction (Table 2).

3.3. Precordial ST depression in right coronary versus left circumjlex related inferior acute myocardial infarction (Table 2)

3.4. Criteria to predict left circumjex-related inferior acute myocardial infarction (Table 3)

The ST level in Vl was higher in the right coronary group than in the left circumflex group (P < 0.001). Eleven of the 18 patients (61%) in the circumflex group versus 12 of the 77 patients (16%) in the right coronary group had more than 0.1 mV ST depression in Vl (P = 0.001). In both groups the precordial ST depression appeared deeper in V3 than in Vl but paired comparison betweenVl and V3 showed that this trend is only

Lateral ST elevation in V5,6 had a sensitivity of 56% and specificity of 92% to predict left circumflex related acute myocardial infarction. Including the lateral limb leads I and AVL, the sensitivity of lateral ST elevation in any of the four lateral leads increased to 61%. In comparison, the absence of lateral T inversion in I and AVL was even more

Table 3 Use of electrocardiographicparametersin predicting left circumflex related inferior acute myocardial infarction Sensitivity (%I Lateral ST? in ST? in ST? in

Specificity (%I

Positive predictive accuracy (%)

Negative predictive accuracy (%)

ST elevation (>O.l mV) leads V5 or V6 leads I or AVL any of the lateral leads

56 6 61

92 100 92

63 100 65

89 82 91

Lateral T inversion Absence of Tk in leadsV5 and V6 Absence of T& in leads I and AVL Absence of Tk in all lateral leads

100 89 100

6 74 6

20 44 20

100 97 100

Inferior ST elevation ST level in III minus II I 0.1 mV

94

37

23

95

Precordial ST depression in Vl ST depressionin Vl > 0.1 mV

61

84

48

90

C.K. Wong, S.B. Freedman I International

sensitive (89%) though less specific (74%). A criterion of ST level in III minus II I 0.1 mV has a sensitivity of 94% and specificity of 37% in predicting left circumflex related inferior infarction whereas a criterion of ST depression in Vl > 0.1 mV has a sensitivity of 61% and specificity of 84%. 3.5. Application of the electrocardiographic criteria in the new test set (Table 4) Among the 49 patients, 16 had concomitant right coronary and left circumflex disease. The infarctrelated artery was the right coronary in 41 patients and left circumflex in eight patients. Useful parameters that discriminated left circumflex related acute myocardial infarction from right coronary related acute myocardial infarction include lateral ST elevation (38% vs. 7%, P < 0.05), absence of lateral T inversion (50% vs. 15%, P < 0.05), and ST depressionin Vl of more than 0.1 mV (50% vs. 7%, P < 0.05), while the criterion of ST level in III minus II d 0.1 mV did not discriminate the two entities (41% vs. 75%, P = NS). The sensitivity of these criteria in predicting left circumflex related acute myocardial infarction was somewhat less when compared with the original cohort (Table 3, Table 4). Overall, in both cohorts the negative predictive accuracy of the criteria was high but the positive predictive accuracy was only modest (Table 3, Table 4). On multiple logistic regression analysis on all recruited patients, these four parameters were independentpredictors of left circumflex related acute myocardial infarction.

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54 (1996) 5-11

4. Discussion The present study demonstrated new electrocardiographic parameters, apart from lateral ST elevation [5,12,13], that differentiated left circumflex related inferior acute myocardial infarction from right coronary related inferior acute myocardial infarction. In inferior acute myocardial infarction, we have previously reported the relationship between the ST changesin various lead groups on continuous ST monitoring [l l] and found that precordial ST depression generally reflects posterior myocardial ischemia [lo]. In contrast, precordial T wave inversion did not separatepatients with a larger posterolateral jeopardized territory in inferior acute myocardial infarction [7]. In the present study, precordial T wave changes were not different in the two groups of inferior acute myocardial infarction. However, lateral T wave inversion was much more common in right coronary related acute myocardial infarction (74%) compared with left circumflex related acute myocardial infarction (11%). Indeed, the criterion of absenceof T inversion in lead I and AVL was even more sensitive (89%) though less specific (74%) than lateral ST elevation in predicting left circumflex related acute myocardial infarction. We found a higher ST level in Vl but not in V3 with right coronary related acute myocardial infarction. Indeed, a criterion of ST depression in Vl > 0.1 mV predicted left circumflex related acute myocardial infarction, which was comparable to lateral ST elevation. The higher ST level in the

Table 4 The identified electrocardiographic parametersapplied in the new test set Sensitivity (%I

Specificity (%)

Positive predictive accuracy (%)

Negative predictive accuracy (%)

Lateral ST elevation (>O.l mV) ST? in any of the lateral leads (I, AVL,V5,V6)

38

93

50

88

Lateral T inversion Absence of TJ in leads I and AVL

50

85

40

90

Inferior ST elevation ST level in III minus II 5~ 0.1 mV

75

58

26

92

F’recordial ST depression in Vl ST depressionin Vl > 0.1 mV

50

93

57

90

10

C.K. Wang, S.B. Freedman I International

right precordial lead Vl may be explained by right ventricular infarction which occurred in about l/3 of patients suffering an inferior acute myocardial infarction usually from a proximal right coronary artery occlusion [14]. Some patients with right ventricular infarction can have anterior ST elevation [15], although such patients were excluded from the present study. Alternatively, the ST depressionin V 1 with left circumflex related infarction may be due to a more posterior left ventricular extension of the infarct, the ST depression in Vl being a mirror image of posterior ST elevation

[lOI. On the standard limb lead ST changes,previous studies [5,14] suggestedthat lateral ST elevation in I and AVL were more common with left circumflex related acute myocardial infarction. However, this occurred in only one of 18 patients with left circumflex occlusion in the original cohort. Instead, we found that the ST elevation in lead II was relatively higher with circumflex related acute myocardial infarction than with right coronary related acute myocardial infarction. In the original cohort of patients, a criterion of ST level in III minus II 5 0.1 mV has a sensitivity of 94% and specificity of 37% in predicting left circumflex related acute myocardial infarction. Unlike a previous study [5] on a smaller group of patients with inferior acute myocardial infarction which found that the presence of both inferior ST elevation 2 1 mm in two or more leads and lateral ST elevation 2 0.5 mm in one or more leads with an isoelectric or elevated segment in lead I identified circumflex related acute myocardial infarction with good sensitivity and specificity [5], the use of lateral ST elevation in predicting left circumflex related acute myocardial infarction shown in the present study was substantially less. This may be due to a difference in the population studied. That study [5] was based on consecutive patients with inferior acute myocardial infarction undergoing intracoronary thrombolysis excluding only patients with total or subtotal occlusion of both left circumflex and right coronary artery. In contrast, the present study excluded any patients with prior infarction and in the first cohort those with concomitant left circumflex and right coronary artery disease even when they were non-occlusive. We

Journal of Cardiology 54 (1996) 5-11

have demonstrated other electrocardiographic parameters comparable to lateral ST elevation in the differentiation and validated their use in a new test set of patients including those with concomitant right coronary artery disease. These parameters include lateral ST elevation (38% vs. 7%), absence of lateral T inversion (50% vs. 15%), and ST depression in Vl of more than 0.1 mV (50% vs. 7%). In both cohorts, however, the positive predictive accuracy was only modest despite a high negative predictive accuracy. None of the parameters could distinguish between right coronary and left circumflex related infarction with complete certainty, although statistically they were significant independent predictors. Combinations of the criteria in various ways will either improve the sensitivity at the expense of a lowered specificity, or vice versa. In the TAM113 trial which prospectively recruited patients with acute myocardial infarction, 292 patients with inferior acute myocardial infarction were angiographically studied and 79% had right coronary related infarction compared to 21% with left circumflex related infarction [16]. This proportion of patients is similar to the combined cohort of patients in the present study. While the majority of inferior acute myocardial infarction is caused by right coronary occlusion, the present study has indicated the clues to suggest a left circumflex infarction, but this alone would not replace the need of angiography for correct diagnosis.

Acknowledgments

Dr C.K. Wong is supported by the Croucher Foundation Research Fellowship. Dr S.B. Freedman is supportedby the Medical Foundation of the University of Sydney.

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C.K. Wang, S.B. Freedman I International

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