The 12-lead ECG that changed the destination: a paramedic STEMI case breakdown

The call comes in as "indigestion, not settling." A man in his sixties is sitting at his kitchen table, pale and a little sweaty, insisting it is the chili from dinner. He has no chest pain, he says, just pressure "up high" and a bit of nausea. His wife called because he looked wrong. This is the moment where the 12-lead ECG and a possible paramedic STEMI call start, long before anyone says the word STEMI.

The crew can treat this as a GI complaint and do a set of vitals, or they can put on the 12-lead within the first few minutes. In this case they did, and the tracing showed ST elevation in the inferior leads with reciprocal depression. The rest of the call turned on what they did with that information.

Below, we break the call into the decisions that mattered. Clinical specifics will vary with your service's medical directives and your provincial ALS/BLS standards; this is about the thinking, not a protocol.

#Decision one: acquire the 12-lead ECG early, even when the story is soft

Acute coronary syndrome does not always look like a movie heart attack. Older adults, people with diabetes and women more often describe pressure, fatigue, shortness of breath, nausea or jaw and arm discomfort rather than crushing central chest pain.

A useful habit is to treat the 12-lead as a vital sign for anyone whose complaint could be cardiac:

• Acquire it early, ideally before moving the patient, so the tracing is clean and the clock is short.
• Repeat it if symptoms change, after any treatment, and before handover.
• Keep the prior tracings. Evolution between ECGs is often more informative than any single one.

A normal first ECG does not rule out ACS. Changes can develop over minutes.

#Decision two: recognising STEMI and its mimics

In general terms, crews look for new ST elevation in anatomically contiguous leads, often with reciprocal ST depression in opposite leads. Inferior changes like this patient's should prompt thought about right ventricular involvement, and many services include right-sided leads in their approach.

The harder skill is knowing what else produces ST elevation. Common mimics include:

1. Left bundle branch block and ventricular paced rhythms, which distort the ST segment by themselves.
2. Left ventricular hypertrophy, which can show ST elevation in the anterior leads.
3. Benign early repolarisation, often in younger patients.
4. Pericarditis, typically with widespread changes and a different clinical story.
5. Hyperkalaemia and some other metabolic causes.

Mimics are not a reason to talk yourself out of a STEMI. Some, such as a new bundle branch block in the right clinical picture, still warrant urgent discussion with a cardiology team. When in doubt, the safest move is usually to transmit and ask, following your regional STEMI protocol.

#Decision three: transmission and pre-alert

Once the crew had a diagnostic tracing, the destination question changed. In many Ontario regions, a STEMI identified in the field can bypass the closest emergency department for a PCI-capable centre, with the ECG transmitted ahead and the catheterisation lab activated before arrival. Arrangements differ by region, so the bypass criteria and contact pathway that apply are the ones your base hospital sets.

A clean pre-alert is short and structured:

• Patient age and sex, and time of symptom onset
• Key ECG findings and whether a tracing has been transmitted
• Haemodynamic status and any arrhythmia
• Relevant history, especially anything that affects treatment such as bleeding risk
• Estimated time of arrival

The point of pre-alert is that the receiving team can be ready. Every minute of preparation that happens while you are driving is a minute the patient does not spend waiting on arrival.

#What went well, and what nearly went wrong

On this call, the early 12-lead was the critical decision. The patient's own framing ("it's indigestion") was persuasive, and the crew later admitted they had nearly delayed the ECG until the truck.

There was also a near-miss. Partway through transport, the patient became bradycardic and hypotensive. Because the crew had already considered right ventricular involvement from the inferior changes, they were prepared to manage it within their directives rather than reacting from scratch. Anticipation, not speed, made that part of the call calm.

#For training leads: building this into practice

STEMI recognition is often taught as ECG pattern-matching in a classroom. The failure points in the field are different: deciding to acquire the ECG at all, reading it under time pressure, and making a destination decision with an anxious family in the room.

Some ways to train the real problem:

• Use soft presentations. Build cases around nausea, fatigue or "indigestion," not textbook chest pain.
• Mix in mimics. Include LBBB, paced rhythms and early repolarisation so learners practise the "transmit and ask" decision.
• Make the pre-alert part of the scenario. Have learners actually deliver one, then debrief on what was missing.
• Add evolution. Give a normal first tracing and a diagnostic second one, so repeating the ECG becomes a habit.

Scenario-based tools like Imedica let crews rehearse these branching decisions repeatedly, with feedback on timing as well as interpretation, without waiting for the next real STEMI.

#The takeaway

In possible ACS, the 12-lead is treatment, because it decides where the patient goes and how ready that team will be. Acquire it early, repeat it, know the mimics well enough to ask for help, and pre-alert clearly. The rest of the system can only move as fast as that first tracing.

Drafted for Imedica Field Notes. Physician review of this article is pending.