An Interesting ECG Case

56-year-old male presents to the ED with 3 hours of chest pain, 2 months after minimally invasive mitral valve repair. Pre-op angiography showed 40% proximal RCA stenosis; no CABG.

His pain is sharp and worse with deep inspiration. Vitals are stable. Here is his ECG:

The ECG shows a supraventricular tachycardia at 136 BPM. There is mild ST elevation in III with borderline ST elevation in and aVF.

Is he having a STEMI?
No—this is not an inferior STEMI.

This ECG shows:

• Atrial flutter with 2:1 AV conduction, giving a regular narrow-complex tachycardia

• Flutter waves distorting the baseline, especially in the inferior leads

• Apparent inferior ST elevation created by flutter waves, not true ST-segment shift

• When measured from the true isoelectric baseline (between flutter waves), ST segments in II, III, and aVF are essentially isoelectric, without convincing reciprocal changes

The diagnosis became clear when:

• Focused history confirmed the pain was pleuritic, not typical for MI

• A rhythm strip during adenosine produced transient AV block, unmasking classic flutter waves

The final diagnosis: atrial flutter with post-operative pericarditis, mimicking an inferior STEMI.

Clinical Significance

• Atrial flutter after cardiac surgery is common and can:

• Distort the ST segments and simulate inferior STEMI

• Post-op pericarditis:

• Causes pleuritic, sometimes positional chest pain

• May have subtle or obscured ECG changes when flutter is present

Management Lessons

• Be cautious about activating Code STEMI for borderline inferior ST elevation when:

• Pain is pleuritic/positional, and

• The rhythm is suspicious for flutter or other atrial activity

• Adenosine (when safe) can:

• Reveal atrial flutter by inducing transient AV block

• Allow accurate reassessment of true ST segments

Take-home: In post-surgical patients, always interpret ST segments in the context of the rhythm and chest pain characteristics—atrial flutter can convincingly mimic an inferior STEMI.