Definition/Introduction

Patients who initially present with signs and symptoms of unstable angina or non-ST elevated myocardial infarction require risk stratification. The need for this stratification is two-fold. Primarily, it helps in making decisions about patient management. Additionally, it helps predict the likelihood of adverse cardiac events.

The thrombolysis in myocardial infarction (TIMI) score is considered a tool for early risk stratification. According to several trials, notably TIMI 11B and ESSENCE, seven factors help assess the mortality risk and risk of other adverse cardiac events, as listed below.[1]

• Age of 65 years or older
• Presence of at least three risk factors for coronary artery disease (i.e., diabetes mellitus, hypertension, hyperlipidemia, smoking, family history)
• Previous history of coronary stenosis of 50% or more
• Presence of greater than or equal to 2 episodes of angina 24 hours before the presentation
• Aspirin use in the past seven days
• ST-segment deviations greater than or equal to 0.05 mV on initial ECG at admission
• Elevated serum cardiac markers of necrosis

If present, each factor contributes a value of one point toward the TIMI risk score, making it a simple tool that does not require differential weights for each factor. A higher score implies a higher likelihood of adverse cardiac events and/or risk of mortality. The following represents scores paired with the percent risk of mortality, new/recurrent MI, or severe ischemia requiring further invasive cardiac intervention.

• 4.7% for a score of 0/1
• 8.3% for a score of 2
• 13.2% for a score of 3
• 19.9% for a score of 4
• 26.2% for a score of 5
• 40.9% for a score of 6/7

Scores ranging from 0-2 constitute a low risk. Scores from 3-5 are considered intermediate risk. A score of 6 or 7 indicates high risk.[2]

Studies have shown that the TIMI risk score is far superior in providing diagnostic evidence for acute coronary syndrome (ACS) compared to history, physical examination, EKG’s, or biomolecular cardiac markers alone.[3][4]

Issues of Concern

Apart from the TIMI risk score, there are other predictive tools such as the GRACE, PAMI, and CADILLAC risk scores that provide insight into management and mortality risk assessment. Studies have shown that the CADILLAC score was more helpful in predicting six-month to one-year outcomes.[5] However, other studies have shown that the TIMI, CADILLAC, and PAMI scores were superior to the GRACE score in determining high-risk patients in need of cardiac catheterization.[6]

Clinical Significance

The TIMI risk score was found to be predictive of the severity of the vascular disease, making it a powerful tool to predict the potential blood vessels of coronary circulation that could be involved.

A sub-study of PRISM-PLUS compared TIMI risk scores to findings on coronary angiography. The study found that patients who had a risk score of 5 to 7 were significantly more likely to have severe culprit stenosis, multivessel disease, left main coronary artery disease, or visible thrombus compared to those who were in the low-risk score category.[7]

Studies have also noted that of the seven factors that contribute to the TIMI risk score, history of coronary artery disease, age greater than or equal to 65, and deviations in ST-segment on initial EKG’s were more strongly associated with adverse cardiac events as compared to the other factors.[8]

Recent studies have also shown that the amplitude of ST-segment elevation or depression and the degree of cardiac biomarker elevation (troponin T/I) can both be independent factors that could point toward initiating early invasive cardiac procedures.[9]

Nursing, Allied Health, and Interprofessional Team Interventions

Perhaps the greatest utility that the TIMI score has to offer is its ability to guide the management of patients presenting with signs of unstable angina/non-ST elevated myocardial infarctions (UA/NSTEMI).

The TACTICS-TIMI 18 trial compared outcomes of patients presenting with UA/NSTEMI who underwent either early invasive interventions or conservative treatment with medication. After risk stratifying patients, they found that intermediate or high-risk patients who underwent invasive cardiac intervention showed a significant decrease in death, nonfatal MI, and rehospitalization for cardiac events compared to those who were medically managed. There was no significant difference in outcome between low-risk patients who received early intervention and those who received medical management.[10]

The timing at which certain complications enfold has been another factor of interest. The TIMI 11b and ESSENCE trials have shown that nearly one-third of myocardial infarctions and half the number of deaths occur after the first week of presentation. Further studies have taken data from these trials and have shown that nearly a quarter of adverse cardiac events occur within 6 weeks following discharge.[8] Patients who were stratified as high risk had a greater likelihood of presenting with adverse cardiac events. However, high-risk patients treated with enoxaparin had a significantly reduced risk of major cardiac events on discharge compared to patients treated with unfractionated heparin.[1]

The PRISM-PLUS study sought to highlight the importance of glycoprotein IIb/IIIa inhibitors. The study showed a significant benefit of the use of glycoprotein IIb/IIIa inhibitors with aspirin and heparin in patients with a TIMI score of greater than 4 compared to management with aspirin and heparin alone. Glycoprotein IIb/IIIa inhibitors were shown to decrease the level of myocardial injury, as measured by peak troponin and creatinine kinase levels.[7]

In conclusion, early invasive management, such as cardiac angiography and revascularization, is recommended for patients presenting with a TIMI risk score greater than or equal to 3. Patients with a TIMI risk score of 0 to 2 should be managed medically.