Activate or Wait – 002
74-year-old male with left scapular pain and nausea.
We are 20 minutes from your tertiary centre.
ECG interpretation
High lateral occlusion myocardial infarction (OMI)
- ST elevation in leads I, aVL, V1-2
- Prominent reciprocal ST depression in lead III
- Hyperacute T waves in V1-2
- Trace ST elevation in V5-6 may be due to lateral wall involvement or pre-existing early repolarisation
This characteristic pattern of ST segment changes resembles the South Africa Flag and is usually caused by occlusion of the first diagonal branch of the LAD (LAD-D1).
There is no lead that directly reflects the “high lateral region” usually supplied by the LAD-D1 vessel. Infarction of this territory therefore often causes subtle ST segment changes that fail to meet STEMI criteria. Lead III is directly reciprocal to this region, and thus ST depression and T-wave inversion in lead III is often more pronounced than any ST elevation seen elsewhere (see both ECGs).
Left circumflex artery occlusion can also cause this ECG pattern, but often produces ST depression in V2-4 reflective of posterior OMI.
AI interpretation by PMcardio
PMcardio’s AI ECG model identified a STEMI/STEMI equivalent.
The explainability feature offers insights into problematic patterns in the respective leads, providing a clear rationale for the diagnosis.
Further reading
Outcome
Given proximity to arrival, no activation call was made. The cardiology team met the patient on arrival and a second ECG was performed:
The patient was taken to the cardiac cath lab
Key finding:
LAD-D1 occlusion
Findings:
- Left Main Coronary Artery – Irregular
- Left Anterior Descending Coronary Artery – 70% proximal stenosis, LAD-D1 complete occlusion
- Left Circumflex Coronary Artery – Irregular
- Right Coronary Artery – Dominant, irregular
Recommendation:
PCI to LAD-D1 and LAD
Clinical Pearls
- The South Africa Flag Sign should be in every critical care practitioner’s knowledge base as a “STEMI-equivalent”, regardless of the magnitude of ST-segment changes seen. The apparent non-contiguous nature of ST elevation means this pattern can be overlooked even by experienced Emergency Physicians.
- Lead III: the most accurate reflector of high lateral OMI
- There is no lead that directly reflects the “high lateral region” usually supplied by the LAD-D1 vessel. Infarction of this territory therefore often causes subtle ST segment changes that fail to meet STEMI criteria. Lead III is directly reciprocal to this region, and thus ST depression and T-wave inversion in lead III is often more pronounced than any ST elevation seen elsewhere.
- ST depression does not localise
- The reciprocal ST depression seen in leads III and aVF is often mistaken for “inferior ischaemia”. One must recall that subendocardial ischaemia does not localise to any one wall, and such localised ST depression here should be assumed to be a reflection of ST elevation in mirror image leads.
References
Further reading
- Smith SW. The resident made the diagnosis immediately. The faculty was not as certain. Dr Smith’s ECG blog.
- Buttner R, Cadogan M. High Lateral STEMI. LITFL
- Buttner R, Aslanger E. ECG Case 121. LITFL
- Nickson C. STEMI Management. LITFL
Online resources
- Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
- Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
- Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
- Rawshani A. Clinical ECG Interpretation ECG Waves
- Smith SW. Dr Smith’s ECG blog.
ACTIVATE or WAIT
EKG Interpretation
Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Co-creator of the LITFL ECG Library. Twitter: @rob_buttner
Dr. Stephen W. Smith is a faculty physician in the Emergency Medicine Residency at Hennepin County Medical Center (HCMC) in Minneapolis, MN, and Professor of Emergency Medicine at the University of Minnesota. Author of Dr Smith's ECG Blog | Bibliography | X |
Dr. Hana Hybasek Dzurikova, MRCVS, PGCert MEd is a medical educator driving innovation and change in health professions education through technology-enhanced learning.