ST elevation myocardial infarction prognosis

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Overview
The prognosis for patients with myocardial infarction varies greatly depending upon simple demographic variables like age, the presence of signs and symptoms of heart failure, the duration of symptoms, and comorbidities that are present. Several risk stratification tools have been developed to predict a patient's mortality. Most of these risk scores are based upon clinical data obtained at the time of admission rather than at the time of discharge.

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:
 * 1) Advanced age
 * 2) Sinus tachycardia
 * 3) Reduced systolic blood pressure
 * 4) Heart failure or Killip class of two or greater
 * 5) 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 randomizaiton (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
Other risk factors include, serum creatinine concentration, and peripheral vascular disease.

Left ventricular function as a risk stratifier
Assesment 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.

STEMI risk scores
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 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 Index incorporates age, HR and SBP (HR x [age/10] x 2/SBP), and has been validated in unselected patients, registries and population-based cohorts

Other risk tools such as the GRACE risk score have also been developed to risk stratify patients.

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.