68F with chest pain. No prior ECG. What is going on here?
This ECG demonstrates all three independent Sgarbossa Criteria for Acute MI in LBBB.
1) ST segment elevation of 1 mm or more that was in the same direction (concordant) as the QRS complex in any lead — score 5. [lead II]
2) ST segment depression of 1 mm or more in any lead from V1 to V3 — score 3. [V2 and V3]
3) ST segment elevation of 5 mm or more that was discordant with the QRS complex (ie, associated with a QS or rS complex) — score 2 [III and aVF]
A Score of >3 was shown to have >90% specificity, acute MI (as judged by CK-MB, not angiography). However, the criteria have had poor sensitivities in validation samples. Either of the first two criteria are sufficient to give a score>3, but the third criteria was too non-specific on its own and thus yields 2 points. Dr. Stephen Smith has suggested (listen to EMCRIT podcast #48) improved sensitivity and specificity for discordant ST elevation in precordial leads, using proportional criteria as defined by the ratio of ST elevation to S-wave depth of ≥ 0.25.
(ECG reproduced from):
Sgarbossa EB, Pinski SL, Barbagelata A, et al, for the GUSTO-1 investigators. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle branch block. N Engl J Med 1996;334:481–7.
Smith SW, Heegaard W, Bachour FB. Acute myocardial infarction with left bundle-branch block: disproportional anterior ST elevation due to right ventricular myocardial infarction in the presence of left bundle-branch block. Am J Emerg Med., 26 (2008), pp. 342–347