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MIA 2012: Smith SW et al. Diagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the S

Posted Jan 01 2013 4:42pm

Bottom Line


Why It’s Important for Emergency Medicine

  • We’ve been told that you just can’t accurately read cardiac ischemia on an EKG in the setting of a LBBB - even when you apply the Sgarbossa criteria. Its specificity is great (~98%), but with a sensitivity of around 20%, you’re missing a whole lot of acute MI’s. 
  • Part of the problem is that LBBBs normally produce an ST-elevation in V1-V4, obscuring your ability to identify anterior MI’s. The original Sgarbossa criteria tries to solve this with its 3rd component: an ST-elevation in excess of 5 mm identifies an acute MI. Well, you can imagine that if the entire EKG suffers from low-voltage, the ST-elevation may not reach 5 mm, and you’d still miss acute MI’s. 
  • As with everything in life, proportions should matter more than absolute size! This universal rule applies to the ST-elevations in LBBBs as well. Using a ratio of ST-elevation / S-wave < -0.25 will identify almost twice as many acute MI’s as using an absolute cutoff. 
Major Points
  • 33 Study EKGs versus 129 matched controls

Sens
Spec
+ LR
- LR
Modified Rule
91
90
9.0
0.1
Original weighted
52
98
22
0.5
Original unweighted
67
90
6.6
0.4

Limitations

As you can see, this study is small. And as if the original Sgarbossa wasn’t hard enough to remember, this modified version is not very “user friendly”...

Reviewed by V. Nguyen

Reference
Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. Diagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the ST-Elevation to S-Wave Ratio in a Modified Sgarbossa Rule. Ann Emerg Med. 2012 Dec;60(6):766-76.  Pubmed

MIA 2012  = Most Interesting Articles series of 2012
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