Management of Rightward Axis ST Changes in Inferior Leads
Patients with rightward axis ST changes in inferior leads should be evaluated for right coronary artery occlusion with possible right ventricular involvement, requiring immediate recording of right-sided chest leads (V3R and V4R) and urgent reperfusion therapy if confirmed. 1
Diagnostic Approach
- ST-segment elevation in leads II, III, and aVF with greater elevation in lead III than lead II suggests right coronary artery (RCA) occlusion rather than left circumflex artery occlusion 1
- When RCA occlusion is suspected, ST-segment depression in leads I and aVL (oriented to the left and superiorly) is often present 1
- Proximal RCA occlusion typically causes right ventricular ischemia/infarction, directing the ST-segment vector rightward, anteriorly, and inferiorly 1
- This rightward axis deviation results in ST-segment elevation in right-sided chest leads V3R and V4R, and often in lead V1 1
Immediate Management Steps
- Record right-sided chest leads V3R and V4R as rapidly as possible after symptom onset, as ST elevation in these leads persists for a much shorter time than in extremity leads 1
- Initiate ECG monitoring immediately to detect life-threatening arrhythmias 1, 2
- Administer aspirin if no contraindications exist 2
- Provide pain relief with titrated IV opioids, recognizing they may slow uptake of oral antiplatelet agents 1
- Administer oxygen only if hypoxemia is present (SaO2 < 90% or PaO2 < 60 mmHg) 1
Reperfusion Strategy
- If ST-segment elevation criteria are met, implement primary PCI strategy within 120 minutes of first medical contact 1, 2
- For patients presenting within 12 hours of symptom onset, reperfusion therapy is indicated 1, 2
- If PCI cannot be performed within 120 minutes and there are no contraindications, consider fibrinolytic therapy 2
Special Considerations
- Patients with proximal RCA occlusion have higher risk of complications including right ventricular infarction 1, 3
- New-onset extreme right axis deviation during acute myocardial infarction may indicate poor prognosis and severe complications 4
- Transient right axis deviation during acute anterior wall infarction has been associated with significant right coronary artery obstruction 5
- ST-segment depression in leads V1-V3 accompanying inferior MI may represent posterior wall involvement, requiring additional posterior leads (V7-V9) to confirm 1, 6
Common Pitfalls and Caveats
- ST elevation in right-sided chest leads associated with right ventricular infarction disappears much faster than inferior ST elevation, so early recording is crucial 1
- Maximal ST-segment depression in left precordial leads (V4-V6) in patients with inferior MI may indicate additional disease in the left anterior descending coronary artery system 7
- Differentiating pathological from physiological ST changes requires consideration of age and gender-specific thresholds 8
- Non-ischemic causes of right axis deviation should be considered in the differential diagnosis, including congenital heart disease, pulmonary embolism, and anatomical variants 9