ECG Case 045

This ECG shows a ventricular paced rhythm with positive Sgarbossa criteria:

• 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.

Sgarbossa Criteria

These criteria allow for detection of myocardial infarction in patients with LBBB and V-paced rhythms (previously thought to be “impossible”).

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.

Sgarbossa Criteria

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.