Which artery is most likely affected in a patient with anterolateral ST elevation and reciprocal changes on an electrocardiogram (ECG)?

Artery Affected in Anterolateral ST Elevation with Reciprocal Changes

In a patient with anterolateral ST elevation and reciprocal changes on ECG, the left anterior descending (LAD) coronary artery is most likely affected, specifically the proximal portion of the LAD above the first septal and first diagonal branches. 1, 2

ECG Pattern Analysis and Vessel Correlation

Anterolateral ST Elevation Pattern

• Anterolateral ST elevation typically appears in leads V1-V4 (anterior) and I, aVL (lateral), indicating involvement of the anterior and lateral walls of the left ventricle 1
• When the proximal LAD is occluded, the ST-segment spatial vector is directed superiorly and to the left, resulting in ST elevation in leads V1-V4, I, aVL, and often aVR 1, 2
• The presence of ST elevation in lead aVL is particularly characteristic of LAD occlusion, with greater elevation in aVL than in aVR 1

Reciprocal Changes

• Reciprocal ST depression occurs in leads positioned opposite to the area of infarction 1, 3
• In proximal LAD occlusion, reciprocal ST depression is typically seen in leads II, III, aVF (inferior leads) and often V5 1
• The magnitude of ST depression is typically greater in lead III than in lead II, reflecting the ST vector's leftward orientation 1
• These reciprocal changes reflect a larger myocardial area at risk rather than additional ischemia in other territories 3

Differentiating Location of LAD Occlusion

Proximal LAD Occlusion

• Involves the basal portion of the left ventricle, anterior and lateral walls, and interventricular septum 1
• ST elevation in V1-V4, I, aVL, and often aVR 1, 2
• Reciprocal ST depression in leads II, III, aVF, and often V5 1
• May show ST elevation in aVR, which is associated with worse prognosis 4

Mid-LAD Occlusion (Between First Septal and First Diagonal)

• Spares the basal interventricular septum 1
• No ST elevation in lead V1 1
• ST vector directed toward aVL (elevated) and away from lead III (depressed) 1
• Less extensive reciprocal changes compared to proximal occlusion 2

Distal LAD Occlusion (Below First Septal and First Diagonal)

• ST elevation more prominent in V3-V6 and less prominent in V2 1
• No ST elevation in V1, aVR, or aVL 1
• No ST depression in leads II, III, or aVF 1
• May even show ST elevation in inferior leads due to inferior orientation of the ST vector 1

Clinical Significance and Prognosis

• Proximal LAD occlusion carries higher risk due to larger area of myocardium at risk 2, 3
• Patients with reciprocal ECG changes have larger areas at risk and higher myocardial salvage potential with timely reperfusion 3
• The presence of ST elevation in aVR in addition to anterolateral changes may indicate more severe disease with worse prognosis 4
• Anterior STEMI patterns are highly predictive (97-100%) of LAD occlusion in patients with single-vessel disease 5

Diagnostic Pitfalls to Avoid

• Do not confuse anterolateral ST elevation with high lateral MI (circumflex occlusion), which typically shows ST elevation in leads I and aVL without significant anterior involvement 1
• Be aware that extensive anterior ST elevation with reciprocal inferior ST depression can occasionally result from distal occlusion of a very long "wrap-around" LAD that supplies the inferior wall 1
• ST elevation in V1 is a key differentiator between proximal and mid-LAD occlusions - its absence suggests mid-LAD rather than proximal occlusion 1, 2
• Do not mistake reciprocal changes for additional ischemia in other territories, as they reflect the electrical forces from the primary area of injury 3, 6