Are ST changes in leads II, III, and aVF (augmented voltage unipolar left foot) indicative of inferior heart ischemia?

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ST Changes in Leads II, III, and aVF Are Indicative of Inferior Heart Ischemia

ST-segment elevation in leads II, III, and aVF is strongly indicative of inferior wall myocardial ischemia/infarction, typically resulting from occlusion of either the right coronary artery (RCA) or left circumflex coronary artery (LCx). 1

Anatomical Basis and Vessel Involvement

  • Inferior wall infarction with ST-segment elevation in leads II, III, and aVF results from occlusion of either the right coronary artery (RCA) or the left circumflex coronary artery (LCx), depending on which provides the posterior descending branch (i.e., which is the dominant vessel) 1
  • When the RCA is occluded, the spatial vector of the ST segment is usually directed more to the right, resulting in greater ST-segment elevation in lead III than in lead II 1
  • RCA occlusion is often associated with reciprocal ST-segment depression in leads I and aVL, which have positive poles oriented to the left and superiorly 1

Differentiating Between RCA and LCx Occlusion

  • In RCA occlusion, ST elevation is typically greater in lead III than in lead II, with associated ST depression in leads I and aVL 1, 2
  • In LCx occlusion, the ST segment may be elevated to a greater extent in lead II than in lead III and may be isoelectric or elevated in leads I and aVL 1
  • The arithmetic sum of ST segments in leads III + V2 < 0 has 90% sensitivity and 100% specificity for LCx occlusion 3
  • The arithmetic sum of ST segments in aVF + V2 > 0 has 86.9% sensitivity and 100% specificity for RCA occlusion 3

Right Ventricular Involvement

  • When the RCA is occluded in its proximal portion, right ventricular ischemia/infarction may occur 1
  • This causes the spatial vector of the ST-segment shift to be directed to the right and anteriorly, as well as inferiorly 1
  • Right ventricular involvement results in ST-segment elevation in right-sided chest leads V3R and V4R, and often in lead V1 1, 4
  • Lead V4R is particularly valuable in diagnosing right ventricular involvement in the setting of an inferior wall infarction 1

Associated Findings and Complications

  • ST-segment depression in leads V1, V2, and V3 occurring with inferior wall ischemia/infarction may indicate posterior (now termed lateral) wall involvement 1
  • This pattern can occur with occlusion of either the RCA or LCx 1
  • When a dominant RCA is occluded proximally, left posterolateral and right ventricular wall involvement may be present 1
  • The posteriorly directed ST-segment vector associated with posterolateral involvement may cancel the ST-segment elevation in lead V1 anticipated by right ventricular involvement and vice versa 1

Important Clinical Considerations

  • Right-sided chest leads V3R and V4R should be recorded as rapidly as possible after the onset of chest pain in patients with inferior ST elevation, as ST elevation in these leads persists for a shorter time than the ST elevation in the inferior leads 1
  • The American Heart Association and American College of Cardiology recommend recording right-sided chest leads V3R and V4R in all patients presenting with ECG evidence of acute inferior wall ischemia/infarction 1
  • Despite having fewer leads with ST elevation, patients with isolated inferior ST elevation (without anterior involvement) often have better preserved left ventricular function than those with more extensive ST changes 5

Differential Diagnosis

  • Not all ST elevation in leads II, III, and aVF represents myocardial ischemia; other causes include:
    • Acute pancreatitis (rare but documented cause of inferior ST elevation) 6
    • Class IC antiarrhythmic drugs like flecainide and pilsicainide 7
    • Early repolarization (typically shows concave upward ST elevation rather than the domed pattern seen in ischemia) 2

Recommendations for ECG Interpretation

  • ECG machines should be programmed to suggest recording right-sided chest leads V3R and V4R when ST elevation greater than 0.1 mV occurs in leads II, III, and aVF 1
  • The pattern of ST elevation in II, III, and aVF should prompt immediate evaluation for coronary occlusion, with particular attention to whether the RCA or LCx is the likely culprit vessel based on the pattern of ST changes 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

ST Segment Doming in ECG

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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