Emergency Department ECG:
Cardiac Cath Report:
- In patients with left bundle branch block (LBBB) or ventricular paced rhythm, infarct diagnosis based on the ECG is difficult.
- The baseline ST segments and T waves tend to be shifted in a discordant direction (“appropriate discordance”), which can mask or mimic acute myocardial infarction.
- However, serial ECGs may show dynamic ST segment changes during ischemia.
- A new LBBB is always pathological and can be a sign of myocardial infarction.
- Sgarbossa Criteria
- Can help determine if pt with baseline LBBB is having an MI
- Concordant ST elevation > 1mm in leads with a positive QRS complex (score 5)
- Concordant ST depression > 1 mm in V1-V3 (score 3)
- Excessively discordant ST elevation > 5 mm in leads with a negative QRS complex (score 2). This criterium is sensitive, but not specific for ischemia in LBBB. It is however associated with a worse prognosis, when present in LBBB during ischemia.
- A total score of ≥ 3 has a specificity of 90% for diagnosing myocardial infarction.
- During right ventricular pacing the ECG also shows left bundle brach block and the above rules also apply for the diagnosis of myocardial infarction during pacing, however they are less specific.