ACS - ECG

T Wave

• Distribution
  • T wave is normally inverted in aVR; sometimes inverted in III, aVF, aVL, V1
• T-wave inversions in V2-V6 are always pathologic
• Morphology
  • Inverted, symmetric,
  • Transient changes suggests ischemia without infarction
  • Persistent changes suggests infarction (troponin elevation usually seen)
• Pseudonormalization
  • In presence of baseline TWI (within 1 month), reocclusion causes normalization of TWI
  • Should be interpreted as evidence of ischemia

Q Wave

• Q waves do not always indicate infarction (see DDX below)
• Must distinguish normal septal q waves from pathologic Q waves:
  • Normal septal q wave: <0.04s, low amplitude
  • Abnormal septal q wave: >0.04s in I OR in II, III, AND aVF OR V3, V4, V5, AND V6
• Q-wave equivalents in the precordial leads:
  • R-wave diminution or poor R-wave progression
  • Reverse R-wave progression (R waves increase then decrease in amplitude)
    • Must distinguish from lead misplacement
  • Tall R waves in V1, V2 (representing "Q waves" from posterior infarction)

Q Wave (Pathologic) DDX

• Ischemic Q waves
• LBBB
• LVH
• Chronic lung disease
• Hypertrophic cardiomyopathy
• Dilated cardiomyopathy

ST Segment Depression

• DDx: Post. STEMI, Subendocardial Infarct, Ischemia, Reciporical Changes, Strain c LVH, Dig effect
• Contour: Most-->Least concerning for ischemia: Planar/Flat (90%) --> Concave up (33%) --> Downsloping with Asymmetric inverted T-wave (not ischemic/strain pattern)
• Assume posterior STEMI or reciprocal changes to STEMI until proven otherwise
• Indicators of ischemia:
  • >0.5mm depression from baseline (especially >1mm) in two or more contiguous leads
  • Transient depression
  • Morphology that is flat or downsloping
• Strain: 
  
  • tall R wave
  • only in lateral leads (not anterior)
  • "checkbox" or asymmetric TWI
  • down sloping pattern

ST Segment Elevation

• Stage 1
  • Timing: 30min - hours
  • Finding: hyperacute T waves
    • >6mm limb leads
    • >10mm precordial leads
  • Duration: normalizes in days, weeks, or months
• Stage 2
  • Timing: minutes - hours
  • Finding: ST segment elevation
    • ≥0.1mV in two or more contiguous leads
  • Duration: ST segment resolution occurs over 72hrs; completely resolves w/in 2-3wks
• Stage 3
  • Timing: within 1hr; completed within 8-12hr
  • Finding: Q waves
  • Duration: persist indefinitely in 70% of cases

• a: 30min after chest pain onset
• b: 45min after chest pain onset (hyperacute T waves)
• c: 70min after chest pain onset (ST elevation)
• d: 3hr after PCI (ST segment has decreased, TWI incdicates reperfusion)
• e: 5 days after PCI (ST segment back to baseline, TWI is near baseline)

Reciprocal Changes

1. Anterior STEMI
   1. Reciprocal ST-segment depression in at least one of leads II, III, aVF
   2. Occurs in 40-70% of cases
2. Inferior STEMI
   1. Reciprocal ST-segment depression usually present in I, aVL; often in V1-V3
   2. Occurs in 56% of cases
3. Posterior STEMI
   1. Reciprocal ST-segment depression in V1-V4
      1. Differentiate from inf STEMI reciprocal depression based on upright T waves, posterior leads showing STEMI
   2. Often associated w/ ST-segment elevation in II, III, aVF (inferior involvement)

See Also

• ACS - Anatomical Correlation
• ACS - Risk_Stratification

Source

• Electrocardiography in Emergency Medicine. ACEP Textbook.