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Chapter 1. Acute Coronary Syndromes

Ola Oyetayo

Definitions (Circulation 2004;110:e82; Circulation 2007;116:e148; Circulation 2008;117:296)

  • Acute coronary syndrome (ACS): umbrella term, includes all clinical syndromes compatible with acute myocardial ischemia arising from an imbalance in myocardial oxygen supply & demand
  • Classified based on ECG results into ST-segment elevation ACS (STE myocardial infarction STEMI) & non-STE ACS (NSTEACS)
  • NSTEACS classified based on cardiac biomarkers (troponins) into NSTEMI or unstable angina (UA)

Etiology (Circulation 2004;110:e82; Circulation 2007;116:e148; Circulation 2008;117:296)

  • Most common cause is reduced myocardial perfusion due to coronary artery narrowing caused by thrombus formation on a disrupted atherosclerotic plaque
  • In NSTEACS, coronary artery is partially occluded by thrombus; in STEMI, thrombus typically totally occlusive

(N Engl J Med 2009;360:2237; Lancet 2008;372:570; N Engl J Med 2004;350:277; N Engl J Med 2007;357:2482)

  • Atherosclerotic plaque rupture exposes thrombogenic components of the plaque
  • Vulnerable plaques contain numerous inflammatory cells, large lipid core, & a thin fibrous cap
  • Platelets arrive & adhere to the site of rupture → platelets release mediators such as epinephrine, adenosine diphosphate (ADP), thromboxane A2 (TXA2), & thrombin → activate & maintain platelet response
  • Activated platelets are also source of inflammatory mediators: CD40 ligand, P-selectin, & IL-1β
  • Tissue factor initiates extrinsic clotting cascade → enzymatic conversion of fibrinogen to fibrin by thrombin; further stabilizes the thrombus (now cross-linked platelets & fibrin)

Table 1-1 TIMI Risk Score for NSTEACS (JAMA 2000;284:835)
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Table 1-1 TIMI Risk Score for NSTEACS (JAMA 2000;284:835)

Predictor Variables

Points

Risk Category

TIMI Risk Score

14d Rate of MACE (%)

Age ≥65

1

Low risk

0–1

4.7

ST-segment deviation

1

2

8.3

Known CAD (stenosis ≥50%)

1

Medium risk

3

13.2

Aspirin use in past 7d

1

4

19.9

Recent (≤24h) severe angina

1

High risk

5

26.2

Positive cardiac biomarkers

1

6–7

40.9

≥3 CAD risk factors (FH, HTN, ↑chol, DM, active smoking)

1

TIMI risk score (0–7) is calculated by totaling points derived from the predictor variables & assigning a risk category.

FH, family history; HTN, hypertension; DM, diabetes mellitus; CAD, coronary artery disease; MACE, major adverse cardiac event (death, MI, or urgent revascularization).

Risk Stratification (Am Heart J 2009;158:193; JAMA 2000;284:835) guides ACS pharmacotherapy & management

  • STEMI patients have the highest risk of in-hospital & short-term major adverse cardiac events (MACE) & should treat emergently without regard to cardiac biomarkers
  • NSTEACS patients have variable risk profiles classified using one of several risk assessment tools (ex: TIMI risk score → estimates risk of MACE by 14d)

Treatment Goals: early restoration of blood flow to infarct-related artery to prevent infarct expansion (MI) or prevent complete occlusion & MI (in UA); prevention of death & complications; prevention of coronary artery reocclusion; relief of ischemic chest discomfort (Circulation 2004;110:e82; Circulation 2007;116:e148; Circulation 2008;117:296)

Approach to Treatment

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