ECG Findings in Left Main Coronary Artery Disease
The hallmark ECG pattern of left main coronary artery (LMCA) disease is ST elevation in lead aVR combined with widespread ST depression in ≥8 surface leads, particularly when aVR ST elevation equals or exceeds V1 ST elevation. 1, 2, 3
Classic LMCA Pattern Recognition
The diagnostic triad consists of:
- ST elevation in lead aVR (typically >0.05 mV, often ≥0.16 mV) 4
- Diffuse ST depression >0.1 mV in ≥8 surface leads (particularly in inferolateral leads II, III, aVF, V4-V6) 1, 3
- ST elevation in aVR ≥ ST elevation in V1 - this specific relationship distinguishes LMCA from proximal LAD occlusion with 81% sensitivity and 80% specificity 2, 4
The European Society of Cardiology emphasizes that this pattern, especially when coupled with hemodynamic compromise (hypotension, cardiogenic shock, pulmonary edema), strongly suggests multivessel or left main obstruction requiring immediate catheterization 1, 3.
Quantitative Criteria
Measure ST segments at the J-point and apply these thresholds: 2
- aVR ST elevation: ≥0.05 mV is significant; ≥0.16 mV is highly specific for LMCA 4
- Compare aVR to V1: when aVR ≥ V1, suspect LMCA rather than isolated proximal LAD 2, 4
- Count leads with ST depression: ≥8 leads increases specificity for LMCA/severe multivessel disease 1, 3
Higher ST elevation in aVR correlates with worse prognosis - patients with greater aVR elevation have higher mortality rates 4.
Distinguishing LMCA from Proximal LAD Occlusion
Key differentiating features: 1, 2, 4
- LMCA pattern: ST elevation greater in aVR than aVL, with aVR ≥ V1, and more diffuse ST depression (≥8 leads) 2, 4
- Proximal LAD pattern: ST elevation in V1-V4, I, and aVL (with aVL > aVR), plus reciprocal ST depression in II, III, aVF - but typically fewer than 8 leads with depression 1, 3
The American College of Cardiology notes that when proximal LAD occlusion occurs above the first septal and diagonal branches, you see ST elevation in V1 through V4, I, and aVL with reciprocal depression inferiorly, but the pattern differs from LMCA by having less widespread depression and different aVR/V1 relationships 1.
Critical Clinical Context
This ECG pattern carries catastrophic implications: 3
- In-hospital mortality approaches 31% 3
- Approximately 59% have severe multivessel disease 3
- Rapid hemodynamic deterioration is common 3
Immediate management priorities: 1, 3
- Activate cardiac catheterization laboratory immediately without awaiting troponin results 3
- Do not delay for additional testing or risk stratification 1, 3
- Obtain ECG during active symptoms when possible - the pattern may resolve when ischemia abates 2
Important Caveats and Pitfalls
The aVR elevation + diffuse ST depression pattern is NOT 100% specific for LMCA: 5
- One study found only 23% of patients with this ECG pattern actually had LMCA/left main equivalent disease on angiography 5
- Other conditions causing diffuse subendocardial ischemia (severe three-vessel disease, demand ischemia, non-cardiac causes) can produce similar patterns 5
- The term "suspect circumferential subendocardial ischemia" may be more accurate than assuming LMCA 5
However, the clinical approach remains unchanged: Given the catastrophic nature of true LMCA occlusion and the inability to exclude it without angiography, this ECG pattern mandates emergency catheterization regardless of the differential diagnosis 1, 3.
Additional diagnostic considerations: 1, 3
- LMCA occlusion may present without diagnostic ST elevation in some cases 1
- Consider posterior leads V7-V9 if circumflex involvement suspected 1
- Ongoing ischemic symptoms despite non-diagnostic ECG warrant emergency angiography 1
- Isolated proximal circumflex occlusion can occasionally mimic this pattern (rare case reports) 6
Timing matters: 2