See this post for a wide complex that hides ischemic findings.

See this post for a difficult diagnosis in the context of a wide complex.

Case

Here is a patient who had a cardiac arrest. Only approximately 25% of our atraumatic cardiopulmonary arrest patients have a STEMI (40% of v fib arrests) so the diagnosis of STEMI by the ECG is critical for the reperfusion decision. Here is the ECG:

The rhythm is atrial fibrillation. The QRS complex is wide, with a right bundle branch block but only subtle ST elevation in III and aVF, with very subtle reciprocal depression in lead aVL. The second complex in the ECG is a PVC, and is seen in leads I, II, and III. In leads II and III, in which the QRS of the PVC is predominantly negative (S-wave), there is marked discordant (opposite to QRS) ST elevation in leads II and III (inferior), far out of proportion to the preceding S-wave.  I believe (without proof) that appropriate discordance in a PVC should be similar to LBBB, in which the average ST/S ratio is 0.10, and excessive due to STEMI is greater than 0.20.   In lead I there is a positive QRS (R-wave) and reciprocal depression that is similarly discordant to the QRS and out of proportion.

These PVC findings confirm the diagnosis of inferior wall STEMI in this otherwise difficult ECG.

The patient had an RCA occlusion.