We were once taught that the presence of LBBB or ventricular pacing precludes electrocardiographic diagnosis of MI or ischemia. It ain’t necessarily so.
If ST changes of acute STEMI occur in the same direction as secondary ST changes of LBBB, exaggerated ST displacement may be noted. If they occur in the opposite direction highly specific concordant ST changes may be seen, reflecting a “tug o’ war on the stylus.”
For clues to old infarction look for Cabrara’s sign along with qS or Qs complexes.
Pseudoinfarcton patterns can be seen with cardiac memory, fusion and bi-ventricular pacing.
The electrocardiographic clues for infarction in patients with RV pacing differ slightly from those in patients with LBBB.
All the nuances were discussed, and fascinating tracings provided, in two reviews from Cardiology Clinics.