Atherosclerosis and Coronary Artery Disease

Clinical Orientation

A 58-year-old man with diabetes, hypertension, and a 40-pack-year smoking history comes to the clinic with exertional chest tightness that resolves with rest. "It's just heartburn, right?" His lipid panel shows LDL 180, HDL 32. His father had an MI at 52. This patient's coronary arteries have been quietly narrowing for decades. The plaque in his LAD won't stay stable forever. This chapter answers: What mechanism links atherosclerosis and CAD to bedside findings, tests, red flags, and nursing priorities?

What Is Normal?

Healthy endothelium: The single-cell-thick lining of all blood vessels. It produces nitric oxide (vasodilator, antiplatelet), prostacyclin (antiplatelet), and tissue plasminogen activator (clot-dissolving). It prevents platelet adhesion, leukocyte adhesion, and smooth muscle cell proliferation. It is a dynamic, metabolically active organ — not passive plumbing.

Coronary blood flow: The heart extracts ~70% of oxygen from coronary blood at rest (compared to ~25% for most other tissues). This means the heart CANNOT significantly increase oxygen extraction — it must increase blood flow to meet increased demand. This is why coronary flow reserve is critical: the ability to vasodilate and increase flow 3-5× during exertion.

Lipid transport: Lipids travel in lipoproteins. LDL carries cholesterol to tissues (including artery walls) — "bad cholesterol." HDL carries cholesterol from tissues back to the liver — "good cholesterol." The LDL:HDL balance, plus oxidation and inflammation, determines atherosclerosis risk.

What Goes Wrong?

The atherosclerotic process:

1. Endothelial injury/dysfunction: From hypertension (shear stress), smoking toxins, hyperglycemia (AGEs), elevated LDL, inflammatory states. Injured endothelium expresses adhesion molecules.
2. Lipid accumulation: LDL particles enter the vessel wall, become oxidized (oxLDL). Macrophages engulf oxLDL → foam cells → fatty streak (earliest visible lesion).
3. Inflammatory response: Foam cells and T-cells release cytokines, growth factors → recruit more inflammatory cells, stimulate smooth muscle cell migration and proliferation.
4. Plaque formation: Smooth muscle cells produce collagen and extracellular matrix → fibrous cap overlying a lipid-rich necrotic core. This is the mature atherosclerotic plaque.
5. Plaque progression: Plaque grows eccentrically (outward). The vessel lumen is preserved until the plaque occupies ~40% of the vessel area — which is why angiography can miss significant disease. This is "positive remodeling."
6. Plaque rupture/erosion: The fibrous cap can thin and rupture, exposing the thrombogenic lipid core to blood → platelet adhesion, activation, aggregation → thrombus formation. This is the mechanism of acute coronary syndrome.

Stable vs. unstable plaque:

• Stable plaque: Thick fibrous cap, small lipid core, less inflammation. Causes fixed stenosis → stable angina (predictable, exertional).
• Unstable/vulnerable plaque: Thin fibrous cap, large lipid core, abundant inflammatory cells. Prone to rupture → acute coronary syndrome.

Risk Factors

• Major modifiable: Hyperlipidemia (high LDL, low HDL), hypertension, smoking, diabetes, obesity, physical inactivity, atherogenic diet.
• Nonmodifiable: Age, male sex (premenopausal women protected by estrogen), family history of premature CAD, genetics.
• Novel/emerging: Lipoprotein(a), hs-CRP (inflammation marker), homocysteine, chronic kidney disease, chronic inflammatory conditions (RA, lupus, psoriasis).

What Happens Inside the Body

Causal chain — from risk factor to myocardial ischemia:

Risk factors → endothelial injury/dysfunction
→ decreased NO, increased adhesion molecules
→ LDL enters vessel wall → oxidized LDL
→ monocyte adhesion → migration into intima → become macrophages
→ macrophages engulf oxLDL → foam cells → fatty streak
→ smooth muscle cell migration, proliferation, collagen synthesis → fibrous cap
→ plaque growth (eccentric at first, maintaining lumen)
→ severe stenosis → flow limitation during increased demand → stable angina
OR
→ thin-cap plaque rupture/erosion → platelet adhesion/activation/aggregation
→ thrombus formation → partial or complete coronary occlusion
→ partial: unstable angina or NSTEMI
→ complete: STEMI

Key finding: The plaque that causes an MI is often NOT the one causing the most stenosis. Vulnerable plaques may be angiographically modest (<50% stenosis) because they've remodeled outward.

What the Nurse May See

Stable CAD: Chest pressure/tightness with exertion or emotional stress. Relieved by rest or nitroglycerin. Predictable pattern. May have dyspnea equivalent (especially in women, elderly, diabetics).

Asymptomatic CAD: Many patients have significant CAD without symptoms — especially diabetics with autonomic neuropathy. The first manifestation may be an MI or sudden cardiac death.

Risk factor stigmata: Xanthelasma (cholesterol deposits near eyelids), corneal arcus (lipid ring around iris in younger patients), hypertension, central obesity.

Tests and Monitoring

• Lipid panel: Total cholesterol, LDL, HDL, triglycerides. LDL target depends on risk level — very high-risk patients may have LDL goal <70 or even <55 mg/dL. Fasting vs nonfasting — nonfasting is increasingly accepted.
• ECG: May show old Q waves (prior silent MI), LVH, nonspecific ST-T changes. Normal ECG does NOT exclude CAD.
• Stress testing: Exercise or pharmacologic stress with ECG, echo, or nuclear imaging. Detects flow-limiting stenosis.
• Coronary CT angiography: Noninvasive visualization of coronary anatomy and plaque. Calcium scoring quantifies plaque burden.
• Coronary angiography: Invasive gold standard. Visualizes stenosis, guides PCI.

Nursing Priorities

1. Assess for angina: PQRST — provocative/palliative, quality, region/radiation, severity, timing. Unstable features: new-onset, at rest, increasing frequency/duration, not relieved by usual measures.
2. Risk factor modification teaching: This is the most impactful nursing intervention for prevention: smoking cessation (single most effective), heart-healthy diet (Mediterranean, DASH), regular exercise, weight management, medication adherence (statins, antihypertensives, antiplatelets).
3. Medication teaching for statins: Take in evening. Report unexplained muscle pain/weakness (rhabdomyolysis risk — rare but serious). Liver function monitoring.

Red Flags

Common Student Mistakes

1. Thinking normal stress test = no CAD: Stress tests detect flow-limiting stenosis. Non-obstructive vulnerable plaque can cause ACS with a recent normal stress test.
2. Assuming the tightest stenosis causes the MI: Vulnerable plaque with thin cap can rupture at <50% stenosis.