What is acute coronary syndrome?

Acute Coronary Syndrome: Definition and Management

Acute coronary syndrome (ACS) refers to a spectrum of clinical disorders characterized by an imbalance between myocardial oxygen supply and demand, typically resulting from coronary artery narrowing caused by a thrombus that develops on a disrupted atherosclerotic plaque. 1 This condition encompasses three main clinical entities: unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI).

Pathophysiology

ACS results from several key mechanisms:

• Plaque disruption and thrombosis: The most common cause is reduced myocardial perfusion due to coronary artery narrowing from a thrombus that develops on a disrupted atherosclerotic plaque 1
• Coronary vasospasm: Dynamic obstruction of epicardial and/or microvascular vessels 1
• Progressive mechanical obstruction: Severe coronary stenosis without spasm or thrombus 1
• Inflammation: Arterial inflammation can contribute to plaque instability 1
• Oxygen supply-demand mismatch: Increased myocardial oxygen requirements in the presence of fixed, restricted oxygen supply 1

Classification of ACS

ACS is classified based on ECG findings and cardiac biomarkers:

1. ST-segment elevation ACS (STEMI):

   • Persistent ST-segment elevation (>20 min)
   • Reflects acute total coronary occlusion
   • Requires immediate reperfusion therapy 1

2. Non-ST-segment elevation ACS (NSTE-ACS):

   • No persistent ST-segment elevation
   • Includes:
     • NSTEMI: Elevated cardiac biomarkers (troponin)
     • Unstable angina: No elevation of cardiac biomarkers 1

Clinical Presentation

The leading symptom initiating the diagnostic cascade is chest pain or discomfort. However, presentations may vary:

• Typical symptoms: Chest discomfort/pain at rest (affects approximately 79% of men and 74% of women) 2
• Atypical symptoms: Dyspnea, epigastric pain, diaphoresis, nausea, or syncope (more common in women, elderly, and diabetic patients) 2

Diagnosis

Rapid diagnosis is critical for appropriate management:

1. Electrocardiogram (ECG):

   • Should be performed and interpreted within 10 minutes of arrival 3
   • Helps distinguish between STEMI and NSTE-ACS 2
   • ECG changes in NSTE-ACS may include transient ST-segment elevation, ST-segment depression, T-wave inversion, or normal findings 1

2. Cardiac biomarkers:

   • High-sensitivity cardiac troponin is the preferred biomarker 3
   • Serial measurements recommended at 1-2 hours for high-sensitivity assays and 3-6 hours for conventional assays 3
   • Elevated troponin distinguishes NSTEMI from unstable angina 1

3. Clinical assessment:

   • History of coronary risk factors
   • Prior cardiac events
   • Hemodynamic stability
   • Risk stratification using validated tools (GRACE or TIMI Risk Score) 3

Management Strategy

Management depends on the type of ACS:

For STEMI:

1. Immediate reperfusion therapy:
   • Primary PCI is preferred when it can be performed within 90-120 minutes of first medical contact 3, 2
   • If PCI cannot be performed within 120 minutes, fibrinolytic therapy should be administered 2

For NSTE-ACS:

1. Risk stratification to determine management strategy:

   • High-risk features: recurrent ischemia, elevated troponins, dynamic ST changes, diabetes mellitus, high GRACE or TIMI scores 3

2. Invasive strategy timing:

   • Immediate invasive strategy (<2 hours): For patients with severe ongoing ischemia, major arrhythmias, or hemodynamic instability 3
   • Early invasive strategy (<24 hours): For high-risk patients 3
   • Conservative strategy: May be considered for low-risk patients 3

Pharmacological Therapy for All ACS:

1. Antiplatelet therapy:

   • Aspirin: 162-325 mg loading dose, followed by 81 mg daily maintenance 3
   • P2Y12 inhibitor: Ticagrelor (preferred for moderate to high-risk patients), prasugrel, or clopidogrel 3

2. Anticoagulation:

   • Unfractionated heparin, low molecular weight heparin, fondaparinux, or bivalirudin 3

3. Additional medications:

   • Beta-blockers (unless contraindicated)
   • High-intensity statins
   • ACE inhibitors/ARBs (especially for patients with left ventricular dysfunction) 3

Secondary Prevention

Long-term management focuses on:

1. Dual antiplatelet therapy: Typically for 12 months 3
2. High-intensity statin therapy 3
3. Beta-blockers 3
4. ACE inhibitors/ARBs 3
5. Lifestyle modifications: Smoking cessation, diet, exercise, weight management 3

Important Considerations

• Avoid NSAIDs (except aspirin) due to increased risks of mortality and reinfarction 3
• Discontinue P2Y12 inhibitors prior to CABG surgery (5-7 days for clopidogrel) 3
• Monitor for bleeding risk, especially in patients <60 kg or with history of GI bleeding 3
• Continuous ECG monitoring is essential for all ACS patients due to risk of arrhythmias 1

Early recognition and appropriate management of ACS significantly reduce morbidity and mortality, making rapid diagnosis and implementation of evidence-based therapies essential for optimal patient outcomes.