In this Roadside to Resus, we take the 2026 Fifth Universal Definition of Myocardial Infarction back to the patients we see in the ED and pre-hospital setting. We start with the key question, when does myocardial injury become an infarction?

From there, we work through the new primary, secondary and procedure-related MI categories—and why finding the cause matters more than attaching a number to the event.

We also get into the troponin decisions that cause debate on shift. Does a percentage rise mean more than the absolute change? And how should sex-specific thresholds and rapid rule-out pathways fit together?

Then we look beyond classical STEMI criteria for an occluded artery: posterior changes, de Winter's T waves, Wellens, and Sgarbossa in patients with known LBBB or ventricular pacing. We finish with MINOCA, unrecognised MI and a question that still divides clinicians: what should we do with suspected unstable angina when high-sensitivity troponins are negative?

Once again we'd love to hear any thoughts or feedback either on the website or via X @TheResusRoom!

Simon, Rob & James