ST elevation myocardial infarction risk stratification and prognosis
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Five variables explain 90% of the prognosis in STEMI: Advanced age,sinus tachycardia, reduced systolic blood pressure, heart failure or Killip class of two or greater, and anterior myocardial infarction location. Two main risk-stratification scores are used when assessing a patient with ST elevation MI and acute coronary syndromes; the TIMI Risk Score (for STEMI), and the GRACE risk score (for acute coronary syndrome.
Factors Associated with a Poor Prognosis in STEMI
While we as physicians often labor under the impression that we can dramatically change a patient's prognosis, it is noteworthy that 90% of the predictive information regarding 30 day mortality is contained in the following 5 baseline variables that can be modified to only a limited degree: 
- Advanced age
- Sinus tachycardia
- Reduced systolic blood pressure
- Heart failure or Killip class of two or greater
- Anterior myocardial infarction location
Sinus tachycardia, hypotension, Killip class, and anterior MI are all essentially markers of poor pump function on admission. These risk factors for 30 day mortality have been well validated in a multivariate analysis of 41,020 patients in the GUSTO-I trial. Advanced age was the most significant factor associated with higher 30-day mortality. The rate was only 1.1% in the youngest decile (< 45 years) and climbed to 20.5% in patients > 75 (adjusted chi 2 = 717, P < .0001). Other variables most closely associated with an increased risk of mortality were lower systolic blood pressure at randomization (chi 2 = 550, P < .0001), higher Killip class (chi 2 = 350, P < .0001), elevated heart rate (chi 2 = 275, P < .0001), and the presence of an anterior infarction (chi 2 = 143, P < .0001). When taken together, these five baseline characteristics contained 90% of the prognostic information. Other significant though less important factors included previous myocardial infarction, height, time to treatment, diabetes, weight, smoking status, type of thrombolytic, previous bypass surgery, hypertension, and prior cerebrovascular disease. When these variables were combined, a validated model was created which stratified patients according to their mortality risk and accurately estimated the likelihood of death.
Other Prognostic Variables not Identified in GUSTO I
Left Ventricular Function as a Risk Stratifier
Assessment of left ventricular ejection fraction may increase the predictive power of some risk stratification models. The prognostic importance of Q-waves is debated. Prognosis is significantly worsened if a mechanical complication (papillary muscle rupture, myocardial free wall rupture, and so on) were to occur.
There is evidence that case fatality of myocardial infarction has been improving over the years in all ethnicities.
The Smokers Paradox
Interestingly, although tobacco abuse is a risk factor for CAD and STEMI, smoking is associated with a lower risk of mortality among patients who present with STEMI  This is due, at least in part, to the finding that smokers who present with STEMI are, on average, at least a decade younger than non-smokers. Smokers more often have involvement of the right coronary artery rather than the left anterior descending artery as well. Smokers paradoxically have better myocardial perfusion following reperfusion therapy than non smokers .
The TIMI Risk Score
The Thrombolysis in Myocardial Infarction TIMI Risk Score  and TIMI Risk Index  are two prognostic indices that have been validated in clinical trials and epidemiologic studies to predict 30-day mortality among patients with STEMI.
The TIMI risk score for STEMI was created from simple arithmetic sum of independent predictors of mortality weighted according to the adjusted odds ratios from logistic regression analysis. The risk score was derived from 14,114 patients enrolled in the Intravenous nPA for Treatment of Infarcting Myocardium Early II trial (TIME II). The TIMI risk score was subsequently validated in an unselected heterogeneous community population through the National Registry of Myocardial Infarction (NRMI) 3 & 4. The TIMI Risk Score incorporates eight clinical variables (age, systolic blood pressure [SBP], heart rate [HR], Killip class, anterior ST elevation or left bundle branch block on electrocardiogram, diabetes mellitus, history of hypertension or angina, low weight and time to treatment >4 hours) and assigns them a point value based on their odds ratio for mortality.
The TIMI Risk Score was developed and validated in clinical trials of fibrinolytic therapy, but it has also been reported to be prognostic in community-based real-world registries  as well as elderly patients . The TIMI risk score for TIMI is calculated by adding the numbers assigned to the different criteria shown below. The total possible score is 14.
|Demographic data and medical history|
|Age ≥75 years||3|
|Age 65–74 years||2|
|History of diabetes mellitus or hypertension or angina||1|
|Systolic blood pressure <100||3|
|Heart rate >100||2|
|Killip class II–IV||2|
|Weight <67 kg||1|
|Evaluation at presentation|
|Anterior ST elevation or left bundle branch block||1|
|Time to therapy >4 hours||1|
Interpretation of TIMI Risk Score for STEMI
|Score||30 Day Mortality (%)|
GRACE Risk Score
- The Global Registry of Acute Coronary Events (GRACE) risk score for ACS:
- The GRACE risk score was created from a multivariable logistic regression model using ACS patients enrolled in the GRACE registry (N=11389).
- The GRACE risk score was validated using subsequent cohort of patients enrolled in GRACE (n=3972) and the Global Use of Strategies to Open Occluded Coronary Arteries IIb (GUSTO-IIb) trial (n=12142).
Calculation of Grace Risk Score for In-Hospital Mortality
The total GRACE risk score is calculated by adding the points assigned to the different variable shown below. The highest total possible score 363.
|Heart rate (beats/minute)|
|Systolic blood pressure (mmHg)|
|Initial serum creatinine (mg/dL)|
|Cardiac arrest at admission||39|
|Elevated cardiac markers||14|
|ST segment deviation||28|
Interpretation of Grace Risk Score for In-Hospital Mortality
A nomogram for the probability in-hospital mortality has been developed based on the GRACE score. Shown below is the probability of in-hospital mortality by the corresponding GRACE score value.
|Score||Probability of in-hospital mortality (%)|
Grace Risk Score for All-Cause Mortality From Discharge to 6 Months
Calculation of the GRACE Score for All-Cause Mortality From Discharge to 6 Months
The total GRACE risk score is calculated by adding the points assigned to the different variable shown below. The highest total possible score 263.
|Heart rate (beats/minute)|
|Systolic blood pressure (mmHg)|
|Initial serum creatinine (mg/dL)|
|History of congestive heart failure||24|
|History of myocardial infarction||12|
|Elevated cardiac markers||15|
|ST segment depression||11|
|No in-hospital PCI||14|
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