Circulation

ECG CHALLENGE

Acute Inferior Wall Myocardial Infarction: What Is

the Culprit Artery?
Qinghua Chang, MD; Zhaolong Xu, MD; Renguang Liu , MD

ECG CHALLENGE sion is shown in Figure 1. The high-sensitivity cardiac

troponin-I was 0.2618 ng/mL (normal range, 0.0000–
A 68-year-old man presented to the emergency depart- 0.0342 ng/mL). He was immediately transferred to the
ment with sudden-onset chest pain, which had been catheterization laboratory for coronary angiography and
persistent for 8 hours. He had been experiencing ex- percutaneous coronary intervention. According to the
ertional shortness of breath in the preceding year. His ­electrocardiographic information, what are the abnormal
medical history was notable for hypertension, atrial fibril- findings, and what is the culprit artery?
lation, and cerebral infarction. A 12-lead ECG on admis- Please turn the page to read the diagnosis.
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Figure 1. A 12-lead ECG recorded on admission to the emergency department.

 
Correspondence to: Renguang Liu, MD, Cardiovascular Institute of the First Affiliated Hospital of Jinzhou Medical University, Renmin St, Jinzhou, 121000, Liaoning
Province, China. Email liurenguanglaoshi@126.com
For Sources of Funding and Disclosures, see page 1895.
© 2021 American Heart Association, Inc.
Circulation is available at www.ahajournals.org/journal/circ

Circulation. 2021;144:1893–1895. DOI: 10.1161/CIRCULATIONAHA.121.057659 December 7, 2021 1893

 Chang et al ECG Challenge
CASES AND TRACES

Figure 2. An 18-lead ECG with correct limb leads placement recorded after admission.
There is ST-segment elevation in leads II, III, aVF, V7 through V9, V4R, and V5R, suggesting acute inferoposterior wall myocardial infarction with right
ventricular infarction.

coronary angiography (Figure 3) was performed, re-

RESPONSE TO ECG CHALLENGE vealing a 60% left anterior descending (proximal to
The 12-lead ECG on admission shows atrial fibrilla- middle portion) obstruction (Figure 3A) and a 100%
tion. There is ST-segment elevation in leads II, III, aVF, proximal RCA occlusion (Figure 3B), which was suc-
and I, with ST-segment depression in leads aVL and cessfully stented (Figure 3C). The left circumflex cor-
V1 through V6, suggesting acute inferoposterior wall onary artery was patent. Postoperatively, the patient
myocardial infarction. The degree of ST-segment el- received secondary prevention therapies.
evation is greater in lead II than in lead III, suggesting Projection of the frontal plane vector on any lead
left circumflex coronary artery occlusion.1 Paradoxi- axis produces the electrocardiographic pattern dis-
cally, the ST-segment elevation in lead I (QS complex- played in the respective limb lead. The waveforms of
es in leads I and aVL) suggests a lateral wall infarc- limb leads in normal sinus rhythm are shown in Fig-
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tion; however, the precordial leads look more like a ure 4A. In a patient with a right arm–left arm lead
posterior wall than a lateral wall infarction. The limb reversal, the electrocardiographic changes are as fol-
and precordial discordance should raise the suspicion lows (Figure 4B): (1) The P-QRS-T waves are inverted
of the presence of electrode reversal. When limb leads in lead I, namely lead I should be flipped; and (2) the
recorded after admission were normal polarity, the pattern of lead aVR resembles a normal aVL, and
lead III elevations are greater than lead II, as shown lead II resembles a normal lead III. These electrocar-
in Figure 2. The 18-lead ECG confirms posterior wall diographic features in normal sinus rhythm are typi-
(V7–V9) with right ventricular (V4R and V5R) infarction cal and easy to diagnose. When it is complicated by
as well. The electrocardiographic manifestations are arrhythmia and depolarization or repolarization abnor-
consistent with a proximal right coronary artery (RCA) malities, electrocardiographic manifestations of right
occlusion.1,2 Such changes also confirm right arm–left arm–left arm lead reversal are atypical, and it is easy
arm lead reversal on admission ECG. Subsequent to cause a misdiagnosis. In this case of atrial fibrilla-

Figure 3. Coronary angiography.

Coronary angiography showed a 60% left anterior descending (proximal to middle portion) obstruction (A). Coronary angiography showed a 100%
proximal right coronary artery occlusion (B). Coronary angiography after stent implantation revealed that the right coronary artery was patent (C).

1894 December 7, 2021 Circulation. 2021;144:1893–1895. DOI: 10.1161/CIRCULATIONAHA.121.057659

 Chang et al ECG Challenge

CASES AND TRACES

Figure 4. Schematic representation of the limb lead axis direction and electrocardiographic pattern formation.
A, Normal electrode placement, the frontal limb lead axis direction and electrocardiographic pattern. B, A right arm–left arm lead reversal
manifested as follows: (1) Lead I is flipped; and (2) the pattern of lead aVR resembles a normal aVL, and lead II resembles a normal lead III. LA
indicates left arm; LL, left leg; and RA, right arm.

tion, the absence of P waves and greater ST-segment

ARTICLE INFORMATION
elevation in lead II than in lead III result in incorrect
interpretation of the culprit artery and lead to limb and Affiliation
precordial discordance. When the RCA is occluded, Cardiovascular Institute of the First Affiliated Hospital of Jinzhou Medical Univer-
sity, Jinzhou, Liaoning Province, China.
ST-segment elevation is greater in lead III than in lead
II. When the left circumflex coronary artery is occluded, Sources of Funding
Downloaded from http://ahajournals.org by on December 7, 2021

the ST-segment may be elevated to a greater extent None.

in lead II than in lead III.1 ST-segment elevation in the Disclosures
right ventricular leads helps us to identify RCA occlu- None.
sion. At this time, we should suspect the presence
of electrode misplacement, which can help elucidate
the conflicting electrocardiographic findings. Impor- REFERENCES
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Circulation. 2021;144:1893–1895. DOI: 10.1161/CIRCULATIONAHA.121.057659 December 7, 2021 1895