I now have comprehensive, authoritative material from multiple textbooks. Here is a complete guide to ST elevation and STEMI on ECG:
ST Elevation & STEMI - ECG Guide
Why Does ST Elevation Happen?
Severe transmural (full-thickness) ischemia lowers the resting membrane potential and shortens action potential duration in affected myocytes. This creates a voltage gradient between ischemic and normal tissue, generating a current of injury. The ST vector shifts outward toward the epicardium - overlying leads record ST elevation.
Panel A = subendocardial ischemia → ST depression. Panel B = transmural ischemia → ST elevation. (Harrison's, 22e)
Diagnostic Criteria for STEMI (4th Universal Definition, 2018)
New ST elevation at the J-point in ≥2 contiguous leads:
| Leads | Cutoff |
|---|
| All leads except V2-V3 | ≥ 1 mm (0.1 mV) |
| V2-V3 in men ≥40 yrs | ≥ 2 mm (0.2 mV) |
| V2-V3 in men <40 yrs | ≥ 2.5 mm (0.25 mV) |
| V2-V3 in women (any age) | ≥ 1.5 mm (0.15 mV) |
A new (or presumed new) LBBB is treated as a STEMI equivalent.
The presence of reciprocal ST depression in mirror leads strongly supports the diagnosis and helps distinguish true STEMI from mimics. - Symptom to Diagnosis, 4e
Localization by Lead Territory
| Affected Wall | Leads with ST Elevation | Reciprocal Depression | Likely Culprit Artery |
|---|
| Anterior | V1-V4 | II, III, aVF | LAD (proximal) |
| Anterolateral | V1-V6, I, aVL | II, III, aVF | LAD or LCx |
| High lateral | I, aVL | III, aVF | LCx or 1st diagonal |
| Inferior | II, III, aVF | I, aVL | RCA (most common) or LCx |
| Posterior | Reciprocal ST depression V1-V3 + tall R wave | - | RCA or LCx |
| Right ventricular | II, III, aVF + right-sided leads (V3R-V4R) | Lateral leads | Proximal RCA |
| Left main / multivessel | aVR (>0.5 mV) + diffuse ST depression | - | LMCA |
Posterior STEMI tip: ST depression in V1-V3 with a dominant R wave is a "STEMI equivalent" - flip those leads 180° mentally and you'll see the elevation.
Temporal Evolution of ECG Changes
- Minutes: Hyperacute T waves (tall, peaked, broad) - earliest sign, often missed
- Hours: ST elevation develops at the J-point
- Hours-Days: T-wave inversions appear in the same leads as the ST elevation
- Days-Weeks: Pathologic Q waves develop (transmural necrosis)
- Weeks-Months: ST elevation usually resolves; persistent elevation suggests ventricular aneurysm
ACS Pathway (Diagnosis Framework)
Goldman-Cecil Medicine
Pathologic Q Waves (Criteria)
- In V2-V3: Q wave ≥0.02 sec, or QS complex
- In all other leads: Q wave ≥0.03 sec AND ≥1 mm deep, in ≥2 contiguous leads
- Not an indication for reperfusion on their own - compare with old ECG to determine chronicity
Washington Manual
STEMI Differentials - When ST Elevation Is NOT a STEMI
| Cardiac | Non-Cardiac |
|---|
| Pericarditis (diffuse, saddle-shaped, PR depression) | Pulmonary embolism |
| Myocarditis | Hyperkalemia |
| LV aneurysm (persistent STE with old Q waves) | - |
| Hypertrophic cardiomyopathy | - |
| Brugada syndrome (V1-V2, coved pattern) | - |
| Early repolarization (normal variant - J-point notch, no reciprocal changes) | - |
| Prinzmetal/vasospasm angina | - |
| Aortic dissection with coronary involvement | - |
Always get an old ECG for comparison - it is often the single most useful step in sorting out chronic from acute STE.
Special Patterns
- De Winter pattern: J-point depression + upsloping ST depression + tall peaked T waves in precordial leads + ST elevation in aVR - proximal LAD occlusion, treat as STEMI equivalent
- aVR elevation: ST elevation ≥0.5 mV in aVR with diffuse depression elsewhere - 78% sensitive, 83% specific for left main disease
- Posterior STEMI: V7-V9 placement (posterior leads) shows ST elevation >0.5 mm when standard leads only show reciprocal V1-V3 depression
Diagnostic Performance of ECG in Chest Pain
From Symptom to Diagnosis, 4e:
- New ST elevation >1 mm: LR+ = 5.7-53 (very high specificity)
- Any ST elevation: LR+ = 11.2
- 80% of ED chest pain patients with new 1 mm ST elevation have confirmed MI
Key Action Thresholds
- ECG must be obtained and interpreted within 10 minutes of ED arrival when MI is suspected
- Do not wait for troponin results before activating the STEMI pathway - treatment decisions are made on ECG findings
- Thrombolytics are contraindicated in NSTEMI (no benefit, added risk)
- Primary PCI is preferred over thrombolysis when door-to-balloon time can be achieved within guideline targets
Sources: Harrison's Principles of Internal Medicine 22e | Goldman-Cecil Medicine | Rosen's Emergency Medicine | Washington Manual of Medical Therapeutics | Symptom to Diagnosis 4e | Textbook of Family Medicine 9e