Although the previous case study was written for formalistic reasons and is admittedly neither very interesting nor particularly original, there is one interesting feature here worthy of note:
The arrows indicate complexes resulting from intermittant LBBB or PVCs with LBBB morphology. The latter is more likely given that their differing frontal plane axes (-60 vs +60) implicate two separate foci.
Despite aberrant conduction, the current of injury resulting from the anterior infarct remains explicit and is diagnostic of coronary occlusion.
In the first EKG (04:15) the complexes in V2 and V3 show appropriately discordant STE, but the ST/S ratio is groselly excessive. In 2010, Dodd and colegues demonstrated that an ST/S ratio >0.2 carries high specificity for LAD occlusion (1). Note the ratios in this case:
V2: ST/S = 6mm/7mm = ~0.86
V3: ST/S = 5.5mm/11mm = 0.5
In the second EKG (07:10) there is >1mm concordant STE in V4 and V6. In LBBB, the ST segments should always be discordant, and, when the terminal R wave is positive, they should show an appropriate proportion of ST depression. Thus, even in V6 where the J-point is isoelectric, there is a conspicuous absence of ST depression. This is a STEMI equivalent (2). Even if this patient had a baseline LBBB and the entire EKG showed wide-complex aberrancy, the MI would not be hidden.
These features as illustrated here closely reflect the more thorough and authoratative work of Dr. Smith in his May 21, 2011 blog post, “LBBB: Is There STEMI?”
Reproduced from his text:
Smith modified Sgarbossa rule:
- At least one lead with concordant STE (Sgarbossa criterion 1) or
- At least one lead of V1-V3 with concordant ST depression (Sgarbossa criterion 2) or
- Proportionally excessively discordant ST elevation in V1-V4, as defined by an ST/S ratio of equal to or more than 0.20 and at least 2 mm of STE. (this replaces Sgarbossa criterion 3 which uses an absolute of 5mm)
- Dodd KW. Aramburo L. Broberg E. Smith SW. For Diagnosis of Acute Anterior Myocardial Infarction Due to Left Anterior Descending Artery Occlusion in Left Bundle Branch Block, High ST/S Ratio Is More Accurate than Convex ST Segment Morphology (Abstract 583). Academic Emergency Medicine 17(s1):S196; May 2010.
- Dodd KW. Aramburo L. Henry TD. Smith SW. Ratio of Discordant ST Segment Elevation or Depression to QRS Complex Amplitude is an Accurate Diagnostic Criterion of Acute Myocardial Infarction in the Presence of Left Bundle Branch Block (Abstract 551). Circulation October 2008;118 (18 Supplement):S578.
- Dr. Stephan Smith. “LBBB: Is There STEMI?” Dr. Smith’s ECG Blog. http://hqmeded-ecg.blogspot.com/2011/05/lbbb-is-there-stemi.html