3.3 Ischemic Changes, Injury & Infarction Patterns

Ischemic Changes, Injury & Infarction Patterns

Identify ischemic changes/infarction is a core CCI CCT analysis task. Cardiographic technicians are often the first professionals to see a tracing that should trigger a STEMI alert. You must recognize the waveform stages of acute coronary syndrome, map ST-T changes to coronary territories, and know when to add right-sided or posterior leads.

The Ischemia–Injury–Infarction Continuum

These stages can coexist on one ECG because different regions may be at different points in the timeline.

ST Segments and Contiguous Leads

ST deviation is measured at the J point (QRS end / ST start) relative to the TP or PR baseline.

Contiguous leads view anatomically adjacent walls:

• Inferior: II, III, aVF
• Anterior/septal: V1–V4
• Lateral: I, aVL, V5–V6
• Posterior: V7–V9 (or infer from V1–V3 mirror images)

Acute injury is reported when ST elevation (or equivalent) appears in two or more contiguous leads. Exact millimeter cutoffs vary slightly by lead, sex, and age in full clinical guidelines; for CCT mastery, emphasize contiguous-lead logic, territory maps, and reciprocal changes rather than memorizing every sex-specific millimeter table.

Territory Localization Table

STEMI Pattern Recognition

STEMI-pattern injury:

• Convex or straight ST elevation in an anatomic group of leads
• Often with reciprocal ST depression in opposite leads
• May begin with hyperacute T waves before frank ST elevation

Reciprocal change example: Inferior ST elevation in II/III/aVF with ST depression in aVL strongly supports acute inferior injury rather than early repolarization mimicry.

NSTE-ACS Patterns

Not all ischemia elevates the ST segment:

• Horizontal or downsloping ST depression ≥ 1 mm in two contiguous leads
• Deep symmetrical T-wave inversion
• Transient ST elevation that resolves

These patterns still require urgent clinical evaluation even when a formal STEMI activation pathway is not met.

Pathologic Q Waves

A pathologic Q wave suggests myocardial necrosis (age may be acute, recent, or old):

• Common teaching thresholds: Q wave ≥ 0.04 seconds (1 small box) wide and/or ≥ 25% of the following R-wave height in a lead that should not normally have a deep Q.
• Small septal q waves in I, aVL, V5–V6 can be normal.

Posterior and Right-Ventricular Extensions

Posterior MI

Anterior leads may show:

• Horizontal ST depression in V1–V3
• Tall R waves in V1–V2
• Upright T waves in V1–V2

Confirm with posterior leads V7–V9. Do not dismiss isolated anterior ST depression as "nonspecific" without considering posterior injury.

Right-Ventricular MI

Suspect with inferior STEMI, especially when III shows more elevation than II. Record right-sided leads; V4R is the highest-yield single lead. RV infarction changes preload management, so early recognition matters.

Common STEMI Mimics Technicians Should Flag Carefully

• Early repolarization (young patients; concave ST elevation, no reciprocal depression)
• Pericarditis (diffuse ST elevation, PR depression)
• LBBB or paced rhythm (use lab protocols for Sgarbossa/modified criteria; do not "clear" these tracings casually)
• Hyperkalemia (wide QRS, peaked T waves)
• Lead misplacement

When uncertain, obtain a technically perfect repeat ECG, compare with priors, and escalate per facility STEMI pathway.

Technician Action Checklist

1. Ensure accurate lead placement—false infarct patterns are commonly technical.
2. Print a baseline-stable tracing without tremor or wander.
3. If inferior STEMI pattern appears, add right-sided leads.
4. If posterior MI is suspected, add V7–V9.
5. Notify the supervising nurse/physician immediately for STEMI-criteria tracings; time stamps and serial ECGs (every 10–15 minutes when symptoms persist) are part of quality care.
6. Never delete an abnormal tracing because it "looks wrong"—document and escalate.

Ischemia and infarction recognition is where ECG technique meets emergency action. Pair this section with coronary anatomy (LAD/RCA/LCX territories) and special lead placement (V4R, V7–V9) for complete Domain C coverage.