Lesson 3.1: Coronary Artery Disease and Acute Coronary Syndromes

Introduction

Coronary artery disease (CAD) is a leading cause of morbidity and mortality in many populations. Understanding the presentations and management of acute coronary syndromes (ACS) is vital for any healthcare provider, especially in internal medicine. This lesson will cover stable angina, non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI) concerning their presentation, electrocardiogram (ECG) findings, biomarker interpretation, triage strategies, and management.

Learning Objectives:

Describe the presentation, ECG findings, and biomarker interpretation in stable angina, NSTEMI, and STEMI.
Explain both acute and long-term management strategies, including reperfusion timing and secondary prevention measures.
Identify and recognize complications arising from myocardial infarction.
Distinguish stable angina from acute coronary syndromes using clinical vignette data.
Select appropriate acute management and reperfusion strategies based on patient presentation and timing.

Section 1: Understanding Coronary Artery Disease

Coronary artery disease occurs when there is a buildup of plaque in the coronary arteries, leading to reduced blood flow to the heart muscle. This can result in various clinical presentations ranging from stable angina to acute coronary syndromes.

1.1 Anatomy and Physiology of the Coronary Arteries

The coronary arteries supply blood to the heart muscle. They branch off from the aorta just above the aortic valve: the left coronary artery (LCA) and the right coronary artery (RCA). The LCA further divides into the left anterior descending (LAD) artery and the left circumflex (LCx) artery.

1.2 Pathophysiology of Coronary Artery Disease

Atherosclerosis is the primary process behind CAD, characterized by the accumulation of lipids, inflammatory cells, and fibrous elements leading to plaque formation. Risk factors include hypertension, diabetes, hyperlipidemia, smoking, and family history.

Section 2: Acute Coronary Syndromes Overview

Acute coronary syndromes (ACS) encompass a range of situations associated with sudden reduced blood flow to the heart.

2.1 Classifications of Acute Coronary Syndromes

Stable Angina: Predictable chest pain triggered by exertion, relieved by rest or nitroglycerin.
NSTEMI: Non-ST-elevation myocardial infarction, where there is myocardial necrosis without ST elevation on ECG.
STEMI: ST-elevation myocardial infarction characterized by full occlusion of a coronary artery with elevation in ST segment on ECG.

2.2 Common Presentations

Example: Presentation of Angina

Symptom: Chest pain or discomfort, often described as pressure or squeezing.
Relief: Typically resolved with rest or nitroglycerin.

Section 3: ECG Interpretation

ECG plays a crucial role in diagnosing acute coronary syndromes.

3.1 ECG Features of ACS

Stable Angina: Generally shows no significant changes on the ECG except during episodes of pain—can demonstrate ST segment depression during stress testing.
NSTEMI: Often shows ST segment depression; T wave inversion may also occur.
STEMI: Characterized by ST segment elevation ($\Delta ST > 1$ mm in contiguous leads) and may lead to Q waves formation over time.

3.2 Worked Example

Consider a patient presenting with chest pain at rest, with the following ECG:

Lead II shows ST elevation of $2$ mm.

This indicates a possible STEMI; immediate management is required.

Section 4: Biomarkers in Diagnosis

Biomarkers are crucial for confirming myocardial infarction.

4.1 Types of Biomarkers

Troponin: High sensitivity and specificity for cardiac injury. Levels rise within 3-6 hours, peak at 12-24 hours, and can remain elevated for 1-2 weeks.
CK-MB: Less specific than troponin but useful for diagnosing reinfarction.

4.2 Example of Biomarker Interpretation

Troponin level is measured as $0.2 \, ng/mL$ (normal is <0.01 ng/mL) at presentation. This indicates significant myocardial injury consistent with NSTEMI or STEMI.

Section 5: Management Strategies

Management of CAD and ACS includes both acute and long-term strategies.

5.1 Acute Management

Stable Angina: Initiate nitroglycerin, beta-blockers, and refine risk factors.
NSTEMI: Administer antiplatelets (aspirin, clopidogrel) and consider angiography within 72 hours.
STEMI: Immediate reperfusion is critical; utilize percutaneous coronary intervention (PCI) or thrombolytics if PCI is unavailable.

5.2 Long-term Management

Lifestyle Modifications: Smoking cessation, diet, and exercise.
Medications: Statins, ACE inhibitors, beta-blockers, and antiplatelet agents.

Section 6: Complications of Myocardial Infarction

Recognizing complications is essential for timely intervention.

6.1 Common Complications

Heart Failure: Reduced cardiac output; management includes diuretics and inotropes.
Arrhythmias: Monitor for ventricular tachycardia or fibrillation; treat accordingly.
Cardiogenic Shock: Reduced perfusion leading to multi-organ failure; consider mechanical support.

Conclusion

Understanding coronary artery disease and acute coronary syndromes is essential for effective triage and management in clinical practice. Early recognition and appropriate management can significantly improve patient outcomes.

Study Notes

Coronary artery disease is primarily due to atherosclerosis.
Acute coronary syndromes include stable angina, NSTEMI, and STEMI.
ECG interpretation is crucial; recognize ST segment changes.
Biomarkers like troponin are essential for diagnosis.
Management involves both acute and long-term strategies focusing on prevention and rehabilitation.