Lesson 3: Ischemia

Summary of Learning Points

• Definitions myocardial injury vs ischemia vs infarct

  • Injury - troponin rise due to some insult (+/- ischemia) 

    • E.g STEMI (ischemic), myocarditis (nonischemic)

  • Ischemia - insufficient O2 to myocardium (+/- infarct; +/-injury)

    • Symptoms (e.g. Chest discomfort), new ECG changes, new wall motion abnls, or new thrombus

    • E.g. STEMI (infarct+injury), stable angina (no infarct, no injury)

  • Infarct

    • Myocardial necrosis from ischemia

    • E.g. STEMI, NSTEMI

• ECG accuracy can vary immensely depending on numerous factors (reader experience, lead placement, timing of ischemia, underlying arrhythmias, artifact)

• ECGs evolve in ongoing ischemia

  • Always compare to baseline ECG, and trend ECGs if in doubt

• Pathologic Q waves are deep and/or wide

  • >1mm deep or 25% of QRS

  • >40ms wide

  • Can be seen in NEW or OLD infarct

• ST Elevations

  • >0.1mm in 2 contiguous leads (V2 and V3 threshold higher >0.2mm)

    • exception: STE in avR = BAD (usually 3 vessel disease or L main disease)

  • If you see other ischemic signs like pathologic Q waves, St depressions, TWIs, always look closely for ST elevations

    • Consider posterior infarcts! (get V7-V9 leads, or right sided leads)

  • Localize to coronary distribution (assuming typical anatomy) unlike ST depressions which do NOT localize

  • Usually due to transmural infarct

  • ST elevation morphology

    • Concave (smiley face) = usually not MI e.g. pericarditis

    • Convex (frown) = usually MI

  • Other causes of STE: pericarditis, LBBB (use Sgarbossa's to help dx MI), LVH, strain, Brugada, early repol, aneurysm, PE)

• ST Depressions

  • New horizontal or downsloping depression >0.05mV in 2 or more contiguous leads

  • Does not localize to coronary territory!

  • Suggests subendocardial ischemia 

• T Waves

  • Positive deflection (ventricular repolarization) after QRS

    • EXCEPT: avR, V1, III

  • Hyperacute T waves: TALL, broad, asymmetrically peaked 

    • Ominous sign as it can be first sign in evolving STEMI

  • T Wave inversions

    • >0.1mV in 2 contiguous leads

    • Do NOT localize

    • Can be sign of ischemia

    • can also be seen in non-schemic conditions (strain patterns, PE, myo/pericarditis, cerebral T waves)

  • Wellens Syndrome

    • T wave abnormality occurring during CP-free time c/f CRITICAL L coronary disease

    • Type A = biphasic in V2-V3 (up then down)

    • Type B = deep inverted T waves in precordium

Practice ECG

Answer