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KEY
🔍- Deep Dive
📌- Clinical Application
🔸 - Weak Evidence
🔹 - Strong Evidence
📑 - Evidence summaries
✅ - Recommended treatment
⚠️ - Critical Information
Your sepsis patient is about to be shifted to the ICU. And suddenly it pops up:
“Troponin I – Positive.”
Now what? Cardiology consult? Cath lab activation?
Heparin? DAPT?
Pause.
Let’s break it down.
What is troponin?
Troponin is a protein complex located on the actin filament of striated muscle (skeletal and cardiac). It regulates muscle contraction by controlling the calcium-mediated interaction between actin and myosin.
It has three subunits:
- Troponin C – binds calcium
- Troponin I – inhibits actin–myosin interaction
- Troponin T – binds the troponin complex to tropomyosin
Cardiac-specific isoforms of troponin I (cTnI) and troponin T (cTnT) are expressed only in cardiac muscle, which makes them diagnostically useful.
When myocardial cells are injured (ischemic or non-ischemic) troponin is released into the bloodstream.
Troponin is a sensitive and specific biomarker of myocardial injury, not myocardial infarction.
Why do we care?
Troponin matters because it is far more sensitive and specific for myocardial injury than older biomarkers such as AST, CK, and CK-MB, which are also present in skeletal muscle and therefore less specific.
After a myocardial infarction:
- Troponin levels begin to rise within 2–3 hours
- Peak at 24–48 hours
- Troponin remains elevated for 5–14 days due to slow clearance.
When measured serially after the onset of chest pain, the rise and/or fall of troponin is highly sensitive and specific for myocardial infarction.
According to the European Society of Cardiology (ESC), a significant change is defined as a ≥20% increase when the initial troponin is already elevated, or a ≥50% increase when the initial elevation is small.
A new rise after an initial fall suggests reinfarction.
But is it only MI then?
When troponin was a lousy assay it was a great test.
Now that it’s becoming a great assay, it’s getting to be a lousy test.
— REBEL EM
With older, lower-sensitivity troponin assays, you had to wait at least 6 hours between the initial sample and the repeat value to see a meaningful rise and confidently rule in an MI.
High-sensitivity troponin changed that.
With hs-troponin, a repeat value at 2–3 hours is usually enough to detect a significant change. And a normal hs-troponin at 3 hours has a negative predictive value of ~99% for ruling out acute myocardial infarction.
But that same sensitivity is where the trouble begins.
High-sensitivity assays can now detect troponin even in apparently healthy individuals. To account for this, consensus guidelines define a clinically relevant elevation as a value above the 99th percentile of a normal reference population.
That does not mean that 1% of the population has an MI.
It means the cutoff is statistical, not diagnostic.
Which is why context matters.
A value above the 99th percentile, by itself, does not diagnose MI. It simply tells you that myocardial injury is possible and that the result must now be interpreted through the lens of history, ECG, imaging, and physiology.
So no,
it isn’t only MI.
And assuming that it is , is where trouble starts.
What else can cause elevated troponin I?
Most troponin elevations do not represent myocardial infarction. They reflect global stress on the heart.
Common causes include:
- Myocarditis
- Renal failure
- Sepsis
- Tachyarrhythmias
- Post-cardioversion
- Cardiac trauma
- Pulmonary embolism
- Acute stroke
- Intracranial hemorrhage
- Severe burns
- Rhabdomyolysis
- Skeletal muscle damage in glycogen storage disease
- Assay interference or cross-reactivity
And importantly:
Elevated troponin does correlate with increased mortality.
In most critically ill patients, troponin functions as a death marker rather than an MI marker. In this setting, it reflects how sick the patient is, not what procedure they need — and that distinction is everything.
Why does it matter if we overdiagnose MI?
Because the label isn’t harmless.
- Bleeding risk: Anticoagulation increases bleeding, including rare but catastrophic intracranial hemorrhage.
- Procedural harm: Cardiac catheterization carries risks of bleeding and kidney injury, and stents commit patients to prolonged dual antiplatelet therapy.
- Derails care: Once labeled “MI,” essential procedures get delayed, and attention shifts away from the real problem toward treating an infarction that may not exist.
So how do we know which is which?
There are no perfectly clear-cut rules.
But asking the right questions, in the right order, helps far more than reacting to a lab value.
Firstly Ask: Do you really suspect an MI?
This is the question that should come before the troponin result, not after it.
Because when we use a statistical cutoff (the 99th percentile), some “normal” individuals will inevitably test positive. And because many non-cardiac conditions can raise troponin, interpretation only makes sense when the pre-test probability of ACS is intermediate to high.
So how do we decide that?
We start with the history
Chest pain history matters a lot.
Certain features increase the likelihood of MI:
- Radiation to the right arm or shoulder
- Radiation to both arms
- Pain associated with exertion
- Radiation to the left arm
- Associated diaphoresis
- Associated nausea or vomiting
- Pain worse than previous angina or similar to a prior MI
- Pain described as pressure
Other features make MI less likely:
- Pain described as pleuritic
- Positional pain
- Sharp pain
- Pain reproducible with palpation
- Inframammary location
- Pain not related to exertion
None of these features are absolute.
But taken together, they help you decide whether a positive troponin is signal or noise.
Then comes the ECG
The ECG is not optional. It is the first-line test for suspected myocardial infarction.
Ask a simple question:
Does this ECG show ischemia right now?
ECG findings that suggest myocardial ischemia include:
- ST elevation
- New ST elevation at the J point in ≥ 2 contiguous leads with the following cutoffs:
- All leads except V2–V3: ≥ 1 mm
- V2–V3:
- ≥ 2.5 mm in men < 40 years
- ≥ 2.0 mm in men ≥ 40 years
- ≥ 1.5 mm in women (any age)
- ST depression and T-wave changes
- New horizontal or downsloping ST depression ≥ 0.5 mm in ≥ 2 contiguous leads
- T-wave inversion > 1 mm in ≥ 2 contiguous leads with a prominent R wave or R/S ratio > 1
and/or
- Other patterns suggesting coronary disease
- Wellens syndrome
- de Winter’s pattern
- Left main coronary artery stenosis patterns
- Transient ST-segment elevation
STEMI is defined by
- V2–V3
- ≥ 2.5 mm ST elevation in men < 40 years
- ≥ 2.0 mm in men ≥ 40 years
- ≥ 1.5 mm in women
- Other leads
- ≥ 1 mm ST elevation
A new LBBB in an asymptomatic patient does not constitute a STEMI equivalent. It must be interpreted in clinical context and with ischemic features.
This diagnosis is made on the ECG, not the troponin.
Don’t forget the background risk
Always step back and ask:
- Known CAD?
- Dyslipidaemia?
- Diabetes?
- Hypertension?
- Current smoker?
- Family history of premature CAD?
Risk factors don’t diagnose MI , but they change your threshold for concern.
If, after all of this, you feel the patient most likely does not have an MI, and the current presentation has a clear alternate diagnosis, it is reasonable not to send the troponin.
Because once a number is out there, it’s very hard to ignore
Now let’s say you have decided to send a troponin. And it comes back positive.
Now what?
An elevated troponin by itself is not myocardial infarction.
What does a positive troponin actually mean?
According to the AHA:
Detection of a cardiac troponin value above the 99th percentile upper reference limit is defined as myocardial injury. A rise or fall in Troponin makes it acute.
That’s it.
At this stage, all you know is that myocardial injury exists.
Next question: is this injury an MI?
The 4th Universal Definition makes this very clear:
An acute myocardial infarction requires both:
- Acute myocardial injury (rise and/or fall in troponin)
- Objective evidence of myocardial ischemia
So what evidence are you actually looking for?
- Clinical history suggestive of myocardial ischemia
- New ischemic ECG changes
- New regional wall motion abnormality on echocardiography
- (Technically a fourth option here is identification of a coronary thrombus on cardiac catheterization. However in clinical practice this is not our primary tool)
No ischemic evidence?
Then you do not have an MI, even if the troponin is high.
Focus on treating the underlying cause of myocardial injury.
Now, if you do find evidence of ischemia, you’ve crossed the line from myocardial injury to myocardial infarction.
So the next question becomes:
What type of MI is this?
There are five types of MI. But for bedside decision-making, we really care about two.
Type 1 vs Type 2 MI
Type 1 MI
This is the classic MI.
It is caused by atherothrombotic coronary artery disease, usually triggered by plaque rupture or erosion, leading to acute coronary thrombosis and myocardial ischemia.
This is the MI that benefits from antithrombotic therapy and early invasive strategies.
Type 2 MI
Type 2 MI is very different.
Here, myocardial ischemia occurs due to a mismatch between oxygen supply and demand, without acute plaque rupture or thrombosis.
Common triggers include:
- Sepsis
- Sustained tachyarrhythmias
- Severe anemia
- Hypotension or shock
- Respiratory failure
- Severe hypertension
- Bradyarrhythmias
Can we reliably differentiate Type 1 from Type 2?
Not perfectly. There is no single test that cleanly separates the two.
The distinction is made through context.
And yes — sometimes, even after careful thought, you won’t be sure.
That’s okay.
So how do we treat Type 2 MI?
- Manage the precipitating illness (sepsis, hypoxia, anemia, arrhythmia)
- Aspirin is reasonable in the absence of contraindications
- Transfuse to a slightly higher hemoglobin target if needed (e.g. >8 g/dL)
- Optimize hemodynamics
- Reduce excessive beta-agonist vasopressor stimulation if possible
- Treat severe hypertension if systemic perfusion allows
- Consider cautious beta-blockade to reduce myocardial demand (only if appropriate)
- Routine anticoagulation or emergent coronary angiography is not indicated unless there is suspicion of Type 1 MI.
For patients with Type 2 MI, the goal is demand reduction and supply optimization, not thrombus hunting.
Type 2 MI does not mean “normal coronaries”. Many of these patients have underlying flow-limiting CAD that becomes relevant only when demand rises. Others have structural heart disease that lowers their ischemic threshold.
But that is not an emergency decision.
What matters
1️⃣Do you really suspect an MI?
Assess pre-test probability by taking
History: look for features that
- History matters
- ↑ Likelihood: Exertional pain, Arm radiation, Diaphoresis, Nausea/vomiting, Pressure-like pain, Similar to prior MI
- ↓ Likelihood: pleuritic, positional, sharp, reproducible pain, non-exertional pain
- ECG is first-line
- ST elevation
- New ST elevation at the J point in ≥ 2 contiguous leads with the following cutoffs:
- All leads except V2–V3: ≥ 1 mm
- V2–V3:
- ≥ 2.5 mm in men < 40 years
- ≥ 2.0 mm in men ≥ 40 years
- ≥ 1.5 mm in women (any age)
- ST depression and T-wave changes
- New horizontal or downsloping ST depression ≥ 0.5 mm in ≥ 2 contiguous leads
- T-wave inversion > 1 mm in ≥ 2 contiguous leads with a prominent R wave or R/S ratio > 1
- High-risk patterns: Wellens, de Winter’s, LMCA patterns
and/or
- Assess background risk
- Known CAD, diabetes, hypertension, dyslipidaemia, smoking, family history
If MI is unlikely and a clear alternate diagnosis exists, it is reasonable not to send troponin
2️⃣Is this injury an MI?
The 4th Universal Definition:
- Detection of a rise and/or fall of cTn with at least one value above the 99th percentile URL
And
- Atleast one objective evidence of myocardial ischemia
- Clinical history suggestive of myocardial ischemia
- New ischemic ECG changes
- New regional wall motion abnormality on echocardiography
3️⃣ What type of MI is this?
- Type 1 MI
Caused by acute atherothrombotic coronary artery disease, usually from plaque rupture or erosion with coronary thrombosis.
This is the MI that benefits from antithrombotic therapy and early invasive management.
- Type 2 MI
Caused by myocardial ischemia from an oxygen supply–demand mismatch.
Want to Read More?
- Thygesen, Kristian, et al. "Fourth universal definition of myocardial infarction (2018)." Journal of the American college of cardiology 72.18 (2018): 2231-2264.
- Rao, Sunil V., et al. "2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline for the management of patients with acute coronary syndromes: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines." Journal of the American College of Cardiology 85.22 (2025): 2135-2237.
- Farkas J. Avoiding over-diagnosis and over-treatment of MI in critically ill patients. REBEL EM; May 17, 2014.
- Yartsev A. Use of troponin in critical illness. Life in the Fast Lane / Deranged Physiology; 23 Nov 2015. Last updated 29 Oct 2025.
Disclaimer : For educational use only — always follow your clinical judgment and local protocols.
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