How this instrument works
Age carries one of the heaviest weights of any single item: nothing under 65, two points from 65 to 74, three points at 75 or older. A systolic blood pressure under 100 mmHg is weighted just as heavily, at three points on its own — a low pressure in a fully blocked artery is a sign the heart is already struggling to keep up. A heart rate over 100 and a Killip class of II through IV (any exam sign of heart failure) each add two points. The remaining four findings — a history of diabetes, hypertension, or angina; body weight under 67 kg; anterior ST elevation or a left bundle branch block; and more than four hours from symptom onset to treatment — each add a single flat point. Add every term up and the ceiling is 14.
Morrow and colleagues built this version in 2000 from the InTIME II trial's 14,114 STEMI patients, running a multivariable analysis that found ten baseline variables captured 97 percent of the model's predictive power, then rounded the strongest of them into point values. Age and blood pressure dominate because, in a completely blocked artery, an older or more hemodynamically unstable heart tolerates the insult far worse — and the effect isn't subtle. Mortality in the derivation cohort ran from well under 1 percent at the lowest scores to over a third of patients at the highest, a many-fold spread across the scale.
That's a deliberately different shape from the UA/NSTEMI score elsewhere on this site, where all seven criteria sit flat at one point each and no single item is allowed to dominate. The two conditions aren't the same event at different severities — NSTEMI and unstable angina leave some blood flow intact, while a STEMI means the artery is fully shut — so Morrow's team and Antman's team drew their weights from separate trial populations chasing separate outcome windows. Reach for this calculator only when the presenting diagnosis is a genuine ST-elevation MI; running STEMI numbers through the other tool would blunt exactly the age and blood-pressure signal that matters most here.
- Set Age: 0 points under 65, 2 points for 65-74, 3 points at 75 or older.
- Mark whether systolic blood pressure is under 100 mmHg (3 points) and heart rate is over 100 (2 points).
- Mark Killip class II-IV — any exam sign of heart failure (2 points) — and history of diabetes, hypertension, or angina (1 point).
- Mark body weight under 67 kg, and anterior ST elevation or left bundle branch block (1 point each).
- Mark whether more than 4 hours passed from symptom onset to treatment (1 point), then read the total and its mortality band.
Worked example — age 75+, several criteria present
A 77-year-old with a history of hypertension, a systolic blood pressure of 92 mmHg, a heart rate of 108, Killip class II crackles on exam, anterior ST elevation on the ECG, a normal weight, and treatment started 3 hours after symptom onset. That's age (3) + dmHtnAngina (1) + sbpLow (3) + hrHigh (2) + killip (2) + weightLow (0) + anteriorSteLbbb (1) + delayedTx (0) = 12.
A score of 12 sits near the top of the 0-14 range, well into the band the original study links to over 20 percent 30-day mortality — a steep climb from well under 1 percent at a score of 0. Age and blood pressure alone supplied 6 of those 12 points between them; the rest arrived one or two at a time from the smaller findings, which is the point of building the scale this way — the two heaviest-weighted items dominate the total far more than any single smaller finding could on its own.
Questions
Why do age and blood pressure get up to three points while some other findings get only one?
Because in a fully blocked artery, both turned out to be among the strongest independent predictors of dying within 30 days in the InTIME II data — stronger than most individual exam findings on their own. Giving them a wider range instead of a flat point reflects how much more mortality risk climbs at 75-plus, or with a systolic pressure under 100, compared with a single smaller finding like elevated weight-adjusted risk.
What is a Killip class, and why does it matter here?
It's a bedside classification of heart failure severity in a heart attack, running from I (no signs) to IV (cardiogenic shock). Class II or higher — crackles in the lungs, an extra heart sound, or worse — adds two points here, because any degree of pump failure at presentation signals a larger, more dangerous infarction, second only to age and blood pressure in how heavily it's weighted.
Why does low body weight count as a risk factor?
Lower body weight, under 67 kg in this score, tracked with worse outcomes in the original derivation cohort, likely as a marker for frailty, older age, or reduced physiologic reserve rather than a direct cause of death. It's one of the smaller findings here for that reason — a single flat point, not a driver on the scale of age or blood pressure.
Is this the same TIMI score used for unstable angina or NSTEMI?
No — this site carries a separate calculator for that population, and the two shouldn't be swapped. The UA/NSTEMI version scores seven criteria flat at one point each over a 0-to-7 range; this STEMI version instead gives age, blood pressure, heart rate, and Killip class unequal, heavier weights on top of four flatter one-point findings, over a wider 0-to-14 range. They come from different trials studying different degrees of coronary blockage.
Does 'time to treatment' mean time to the emergency department?
No — it's measured from symptom onset to actual treatment, typically reperfusion therapy, whether that's a catheter procedure or a clot-dissolving drug, not to arrival. A patient who waited six hours at home before calling for help scores this point even if the hospital moved fast once they arrived, because the clock that matters is total ischemic time.
How much does the risk really climb across the scale?
Sharply. The original InTIME II cohort saw 30-day mortality of well under 1 percent at the lowest scores, climbing past 20 percent in the upper-middle of the range and reaching well over a third of patients at the highest scores — a many-fold difference between the lowest and highest bands, which is why this instrument is used to triage urgency rather than just satisfy curiosity.
References
- Morrow DA, Antman EM, Charlesworth A, et al. — Circulation, 2000 (PubMed)
- American Heart Association — Heart Attack
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.