64-year old female presenting with severe chest pain and diaphoresis. Describe the ECG
Describe and interpret this ECG
ECG ANSWER and INTERPRETATION
- There is concordant ST depression in V2-5. This violates the expected pattern of discordance for a V-paced rhythm and is a marker of superimposed myocardial infarction.
- The morphology in V2-5 is reminiscent of posterior STEMI, with horizontal ST depression and prominent upright T waves.
- Multiple non-conducted P waves are seen, indicating the presence of underlying high-grade AV block (probably the indication for pacemaker insertion). However, the fusion complex (beat #5 on rhythm strip) suggests that P waves are occasionally transmitted, arguing against complete heart block.
This patient did indeed have an isolated posterior infarction, due to complete occlusion of a posterolateral branch of the RCA. She was successfully treated with PCI.
Normal Pattern in LBBB / VPR
The expected finding in patients with uncomplicated LBBB / V-paced rhythm is discordance — i.e. the ST segments and T waves point in the opposite direction to the QRS complex.
How To Spot Superimposed MI
Superimposed myocardial infarction is suspected if there is either:
- Loss of the usual pattern of discordance — i.e. concordant ST changes.
- Excessive discordant ST elevation — i.e. out of proportion to what would be expected for LBBB / paced rhythm.
Diagnosis of MI in LBBB / VPR requires at least one of the following criteria to be present:
- Concordant ST depression > 1 mm in V1-3.
- Concordant ST elevation > 1 mm in any lead.
- Excessively discordant ST elevation in any lead >5 mm (original Sgarbossa criteria) or >25% of the corresponding S-wave depth (modified Sgarbossa criteria = more specific).
Changes only have to be present in a single lead to be diagnostic of MI.