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5 Cards in this Set
- Front
- Back
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The rule of appropriate T-wave discordance.
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-the expected relationship between the QRS complex and the ST-segment and T-wave in the setting of left bundle branch should be one of discordance.
-in the setting of left bundle branch block, negatively deflected QRS complexes can be expected to show ST-elevation and upright T-waves -Positively deflected QRS complexes can be expected to show ST-depression and inverted T-waves. -That's why left bundle branch block is an anterior STEMI mimic -It is normal for the ST-segments to be deflected opposite the S-waves in the right precordial leads (V1-V3) |
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Excessive discordance
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-However, there is a limit to how much discordance is appropriate.
-Sgarbossa's criteria requires at least 5 mm of discordant ST-elevation in order to be significant. -However, this criterion is problematic because it does not take into account the rule of proportionality. -That's why it's the weakest of Sgarbossa's critiera. -Discordant ST-elevation of 5 mm (as a stand-alone finding) only indicates a 50% probability of AMI according to Sgarbossa's original scoring algorithm. -discordant ST-elevation = or > 5 mm, is (by far) the least specific of Sgarbossa's criteria. -It's the least specific because it doesn't take into account the depth of the S-wave (rule of proportionality). -In other words, the deeper the S-wave, the greater the ST-elevation, and this is normal. |
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Sgarbossa's criteria to identify AMI in the presence of LBBB
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1.) ≥ 1 mm of concordant ST-elevation (in the same direction as the majority of the QRS complex) in at least one lead
2.) ≥ 1 mm of ST-depression in lead V1, V2 or V3 3.) ≥ 5 mm of discordant ST-elevation (opposite the majority of the QRS complex) in at least one lead |
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Sgarbossa scoring algorithm
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-According to the original scoring algorithm, the more of these criteria that are met, the higher the probability of AMI.
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Modified criterion which considers the ST/QRS ratio.
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-Stephen Smith, M.D. (of Dr. Smith's ECG Blog) uses a modified criterion which considers the ST/QRS ratio.
-He has found that when the ST-segment is deviated more than 0.2 the QRS complex it is both a sensitive and specific marker for acute STEMI in the setting of left bundle branch block (and probably also paced rhythm). |
