In a healthy young patient under general anaesthesia, continuous three‑lead ECG monitoring shows 3 mm ST elevation in leads II and III but not lead I; what is the likely cause?

ST Elevation in Leads II and III During General Anesthesia: Most Likely Non-Cardiac Causes

In a healthy young patient under general anesthesia showing 3mm ST elevation in leads II and III but NOT in lead I, the most likely causes are technical artifacts (lead misplacement, electrode issues) or benign physiologic variants rather than true myocardial ischemia.

Algorithmic Approach to This ECG Finding

Step 1: Rule Out Technical Issues FIRST

• Check for limb lead reversal or misplacement - This is the most common cause of paradoxical ST patterns during monitoring 1
• Verify electrode placement and connections
• Look for unusual P-QRS patterns that suggest lead reversal 1
• Repeat the ECG immediately - if findings normalize, this strongly suggests artifact 2

Step 2: Assess the Clinical Context

The absence of ST elevation in lead I is the critical distinguishing feature here:

True inferior MI pattern (RCA or LCx occlusion) would show:

• ST elevation in leads II, III, AND aVF together 3
• When RCA is occluded: ST elevation greater in lead III than lead II, often WITH ST depression in leads I and aVL 3
• The pattern you describe (II and III elevated, but NOT lead I) is atypical for true ischemia

Step 3: Consider Benign Mimickers in Young Healthy Patients

Atrial repolarization (Ta wave):

• Can cause ST elevation that mimics STEMI, especially with low atrial ectopic rhythms 2
• Resolves spontaneously on repeat ECG 2
• More likely in young patients without cardiac disease

Early repolarization variant:

• Common benign finding in young patients 4
• Can be accentuated during anesthesia
• Typically shows J-point elevation with upward concavity

Constant ST elevation pattern:

• Described in obese middle-aged men with hypertension
• Usually NOT associated with coronary stenosis (only 6.25% had significant disease) 5
• Associated with LV hypertrophy

Critical Pitfalls to Avoid

1. Do NOT activate the cath lab based on 3-lead monitoring alone in a hemodynamically stable patient

2. Do NOT assume ischemia without:

   • Obtaining a full 12-lead ECG immediately
   • Checking troponins (though these lag behind ECG changes)
   • Assessing hemodynamics and clinical context

3. Recognize that general anesthesia masks symptoms - you cannot rely on chest pain to guide diagnosis 4, 6

Immediate Management Steps

1. Obtain a full 12-lead ECG immediately - this is diagnostic
2. Check for hemodynamic instability (hypotension, new wall motion abnormalities on TEE if available)
3. Verify all monitoring leads are correctly placed
4. If 12-lead confirms inferior ST elevation in contiguous leads (II, III, aVF) with reciprocal changes, consider true ischemia
5. If 12-lead shows normalization or different pattern, the 3-lead finding was artifact or benign variant

Why This is Likely NOT Acute MI

• Healthy young patient = extremely low pretest probability
• Only 2 leads involved (II and III) without aVF = does not meet criteria for contiguous lead involvement 3
• Lead I not involved = atypical vector for true inferior ischemia 3
• Under anesthesia = multiple technical and physiologic confounders 6

The threshold for diagnosing STEMI requires ST elevation ≥0.1 mV in at least 2 anatomically contiguous leads 3. While leads II and III are contiguous, the absence of involvement in lead aVF (the third inferior lead) and the unusual sparing of lead I make this pattern highly suspicious for artifact rather than true ischemia 3.