An Unusual ECG Pattern in Mid-Left Anterior Descending Artery Occlusion

Abstract

A 52-year-old dyslipidemic gentleman with no previous cardiovascular symptoms presented with acute typical angina for 4 h. The electrocardiogram (ECG) demonstrated ST-elevation in leads III, aVR, and V1, ST-segment depression in I, aVL, and V6, and hyperacute T-waves in leads V2-V6. Emergent angiography revealed critical single-vessel disease of the mid-left anterior descending artery (LAD) involving the first septal artery (S1) and proximal to the first diagonal artery (D1). This case illustrates how a significant ST-elevation myocardial infarction involving the mid-left anterior descending artery can potentially be underestimated in the electrocardiogram due to vector shifts related to the ramus intermedius artery. ST-elevation in leads III and aVF with upsloping ST-segment depression in V2-V6 may suggest a mid-left anterior descending artery acute anterior wall myocardial infarction in patients with a large ramus intermedius artery or an early obtuse marginal artery.

A 52-year-old dyslipidemic gentleman with no previous cardiovascular symptoms has presented with acute typical angina for 4 h. He was hemodynamically stable at presentation with a pulse rate of 98 beats/min, blood pressure 138/80 mmHg, and a room air oxygen saturation of 99%. The first heart sound was soft; no other abnormalities were appreciated on the precordial examination. The lung bases were clear.

The electrocardiogram (ECG) demonstrated ST-elevation in leads III, aVR, and V1, ST-depression in I, aVL, and V6, and hyperacute T-wave abnormalities in leads V2-V6 (Figure 1). Poor R-wave progression was noted in leads V2-V5. Echocardiography revealed moderate left ventricular dysfunction with hypokinesia of the entire anterior wall and anteroseptum. The left ventricular ejection fraction was 40%. There was no clot in the cardiac chambers, no significant valve regurgitation, or pericardial effusion.

Figure 1.

Twelve-lead Electrocardiogram of the Patient at Presentation with Acute Chest Pain.

The patient was immediately taken up for primary angioplasty. Coronary angiography revealed a right-dominant coronary system. The left main coronary artery was a trifurcating vessel. While the left circumflex and ramus intermedius artery were normal, there was critical single-vessel disease of the mid-left anterior descending artery (LAD) involving the first septal artery (S1) and proximal to the first diagonal artery (D1) (Figure 2a, 2b). The right coronary artery was normal (Figure 2c). A 3.5 × 30 mm Zotarolimus-eluting stent was deployed in the LAD, with good results, and thrombolysis in myocardial infarction (TIMI) grade 3 flow was achieved (Figure 3a). Post-procedure ECG showed resolution of ST-segment changes, partial regeneration of R-waves, and biphasic T-waves in V4 and V5 (Figure 3b). The patient was discharged on day 4 post-angioplasty on dual antiplatelet therapy, high-intensity statin, angiotensin receptor neprilysin inhibitor, mineralocorticoid antagonist, beta-blocker, and sodium-glucose co-transporter-2 inhibitor. He remains asymptomatic at the 6-week follow-up, and the left ventricular ejection fraction improved to 45%.

Figure 2.

Note: AM, acute marginal artery; Cx, left circumflex artery; D1, D2, and D3, first, second, and third diagonal arteries, respectively; LAD, left anterior descending artery; LM, left main coronary artery; RCA, right coronary artery; RI, ramus intermedius artery; RV, right ventricular branch; S1, first septal artery.

Figure 3.

Post-angioplasty Left Coronary Angiogram in Postero-anterior View with Cranial Angulation (Panel a) Demonstrating Good Result. Type 4 Left Anterior Descending Artery (LAD) is Noted. Panel b is the Post-angioplasty Electrocardiogram (ECG) Showing Resolution of ST-segment Changes, Partial Regeneration of R-waves, and Biphasic T-waves in V4 and V5.

The electrocardiogram depicts an unusual yet characteristic pattern with acute occlusion of the mid-LAD. The LAD from its ostium to the first major septal or diagonal is traditionally considered the proximal LAD; mid-LAD refers to the segment from the first major septal or diagonal to the origin of the distal major diagonal artery; distal LAD refers to the segment thereafter till its termination. ¹ ST-elevation in V1, loss of R-waves, and hyperacute T-waves in the anterior precordial leads are markers to suggest an acute LAD occlusion. ²

ST-segment deviation involving leads III and aVF is useful to localize acute LAD occlusion in relation to D1. While the sum of ST-depression in leads III and aVF ≥2.5 mm suggests an occlusion proximal to D1, ST-elevation in leads III and aVF points to an occlusion beyond D1. ³ In the index patient, with the lesion being proximal to D1, the ST-elevation in III and aVF is explained by the large ramus intermedius artery that perfused the diagonal territory. Consequently, the ST vector is directed inferiorly and rightward, mimicking a lesion distal to D1 (Figure 4). The ∑ (ST-segment deviation in aVR + V1 – V6) <0 is a marker of the lesion distal to S1. ³

Figure 4.

Vectorcardiogram Demonstrating the Inferior and Rightward Net ST-vector in the Index Case.

Summary

The absence of ST-elevation in the precordial leads, barring V1, should not preclude the diagnosis of acute anterior wall myocardial infarction. The proposed etiology of the widespread upsloping ST-depression includes endocardial conduction delay related to an anatomical variation of Purkinje fibers, or the lack of activation of sarcolemmal adenosine triphosphate (ATP)-sensitive potassium channels by ischemic ATP depletion.^{4, 5} This case illustrates how a significant ST-elevation myocardial infarction involving the mid-LAD can potentially be underestimated in the ECG due to vector shifts related to the ramus intermedius artery. ST-elevation in leads III and aVF, with upsloping ST-depression in leads V2-V6, may suggest a mid-LAD acute anterior-wall myocardial infarction in a patient with a large ramus intermedius artery or early obtuse marginal artery.