Coronary Artery Disease

Coronary artery disease (CAD) is the single largest killer of adults on Earth. At its heart is a slow, silent process — atherosclerosis — in which cholesterol-laden plaque builds up in the walls of the arteries that feed the heart muscle. For decades this can produce no symptoms at all. Then one day a plaque cracks, a clot forms in seconds, and a person who felt well that morning is having a heart attack. Understanding CAD means understanding this whole arc: the decades of quiet plaque growth, the sudden thrombotic catastrophe, and the narrow window in which the right ECG, the right blood test, and the right catheter can save heart muscle and save a life.

This page teaches CAD the way a good cardiology firm would: the biology of the plaque, the clinical spectrum from stable angina to STEMI, how we read the ECG and troponin, and how we treat — from aspirin to stents. It is educational; real patients need real clinical judgement.

Learning Objectives

• Explain how atherosclerosis develops and why plaque rupture, not just narrowing, causes myocardial infarction.
• Distinguish stable angina, unstable angina, NSTEMI, and STEMI on clinical, ECG, and biomarker grounds.
• List the major modifiable and non-modifiable risk factors and how each is addressed.
• Interpret the core diagnostic tools: the 12-lead ECG and cardiac troponin.
• Outline evidence-based management for chronic coronary disease and acute coronary syndromes.
• Recognise the historical shift from "hardening of the arteries" to the thrombosis theory of MI, and why it changed treatment forever.

Quick Answer

CAD is narrowing of the coronary arteries by atherosclerotic plaque, reducing blood supply to the myocardium. When demand outstrips a fixed supply, patients get stable angina — predictable chest pressure on exertion, relieved by rest. When a plaque ruptures and triggers thrombosis, the result is an acute coronary syndrome (ACS): unstable angina, NSTEMI, or STEMI, depending on whether the vessel is partly or completely occluded and whether myocardium dies. Diagnosis rests on symptoms, the 12-lead ECG (looking for ST elevation or depression), and cardiac troponin (which rises when myocytes die). Management combines risk-factor control, antiplatelet and statin therapy, and — for acute occlusion — urgent reperfusion by primary PCI (stenting) or thrombolysis. Time is muscle.

Where It Came From

Ancient physicians described sudden death and chest pain, but the mechanism was a mystery for millennia. In 1768 the English physician William Heberden gave the first crisp clinical description of angina pectoris — a "strangling" chest discomfort brought on by walking, especially uphill or after meals, and relieved by standing still. He did not know its cause; he even noted that some sufferers dropped dead. Post-mortems by Edward Jenner (later of smallpox fame) and Caleb Parry in the 1780s–90s linked angina to hardened, ossified coronary arteries — connecting the symptom to diseased vessels for the first time.

The word atherosclerosis was coined in the early 1900s (Greek athere, gruel, for the soft lipid core; sclerosis, hardening, for the fibrous cap). The great debate of the twentieth century was: does a heart attack happen simply because a narrowed artery finally clogs, or because something acute occurs? In 1912 the American cardiologist James Herrick published a landmark paper arguing that coronary thrombosis — a sudden clot on top of diseased artery — caused myocardial infarction, and crucially that patients could survive it. His idea was initially ignored; the prevailing view held that coronary occlusion was invariably and instantly fatal.

Herrick was vindicated decades later. Angiographic studies in the late 1970s and 1980s (notably by Marcus DeWood, 1980) showed that most patients in the first hours of a transmural MI had a totally occluded coronary artery with fresh thrombus — proving the thrombosis theory and directly justifying clot-busting and stenting. This is the intellectual bridge that turned MI from a death sentence into a treatable emergency: if a clot causes it, then dissolving or removing the clot fast can stop it. Everything modern — thrombolytics, aspirin, primary PCI — flows from Herrick's insight and DeWood's confirmation. The parallel discovery that high cholesterol drives plaque (the Framingham Heart Study from 1948 onward; the lipid hypothesis; the arrival of statins in the late 1980s) gave us the tools to prevent the plaque in the first place.

Atherosclerosis: How the Plaque Forms

Atherosclerosis is not passive "furring up." It is a chronic inflammatory disease of the arterial wall, and it explains why CAD is both preventable and dangerous.

The sequence, simplified:

1. Endothelial injury and dysfunction. The single-cell lining of the artery is damaged by high LDL cholesterol, hypertension (shear stress), smoking toxins, and hyperglycaemia. Injured endothelium becomes leaky and sticky.
2. Lipid entry and oxidation. LDL particles slip into the intima and are oxidised. Oxidised LDL is highly inflammatory.
3. Foam cell formation. Monocytes enter the wall, become macrophages, and gorge on oxidised LDL — becoming lipid-filled foam cells. These are the earliest visible lesion, the fatty streak, present even in teenagers.
4. Plaque growth. Smooth muscle cells migrate in and lay down a fibrous cap over a soft, lipid-rich necrotic core. This is a mature atheroma.
5. The fork in the road. A plaque can be stable (thick fibrous cap, small lipid core — causes narrowing and angina) or vulnerable (thin cap, large lipid core, lots of inflammation — prone to rupture).

The crucial clinical insight: the plaques that cause heart attacks are often not the most severely narrowing ones. A vulnerable plaque causing only 40% stenosis can rupture and kill, while a stable 80% lesion causes stable angina for years. Rupture exposes the thrombogenic core to blood, platelets aggregate, the clotting cascade fires, and a thrombus forms — the moment Herrick described.

The Clinical Spectrum: From Stable Angina to STEMI

CAD presents along a continuum driven by supply-and-demand and by thrombosis.

Stable angina is demand-led ischaemia against a fixed narrowing. Classic features: central chest pressure, tightness, or heaviness, often radiating to the left arm, jaw, or neck; brought on by exertion or emotion; lasting a few minutes; relieved by rest or GTN (nitroglycerin). It is predictable and reproducible. No myocardium dies.

Acute coronary syndrome (ACS) is thrombosis-led and is a spectrum:

• Unstable angina (UA): angina that is new, worsening (crescendo), or occurs at rest. Partial thrombosis; troponin normal (no infarction yet). A warning shot.
• NSTEMI (non-ST-elevation MI): partial or transient occlusion causing myocyte death. ECG may show ST depression or T-wave inversion (or be normal); troponin is raised.
• STEMI (ST-elevation MI): complete, persistent occlusion of a coronary artery. Full-thickness (transmural) infarction. ECG shows ST elevation; troponin rises. This is the true emergency requiring immediate reperfusion.

Worked clinical vignette. A 58-year-old smoker with diabetes wakes at 5 a.m. with crushing central chest pain radiating to the jaw, sweating and nauseated, unrelieved by rest. In the ambulance a 12-lead ECG shows ST elevation in leads II, III, and aVF. This is an inferior STEMI, almost certainly a right coronary artery occlusion. The clock starts now: the goal is to open that artery, ideally by primary PCI within 90–120 minutes of first medical contact. Every 30 minutes of delay measurably increases mortality and heart-failure risk.

Risk Factors: The Levers We Can Pull

Risk factors are what turn a healthy artery into a diseased one, and most are modifiable.

Modifiable	Non-modifiable
Smoking	Age (risk rises steeply after 45 in men, 55 in women)
Hypertension	Male sex (women partly protected until menopause)
High LDL / low HDL cholesterol	Family history of premature CAD
Diabetes mellitus	Ethnicity (e.g. South Asian populations at higher risk)
Obesity and physical inactivity	Genetic conditions (e.g. familial hypercholesterolaemia)
Poor diet

Smoking and diabetes are especially potent. Diabetes is often called a "coronary risk equivalent" because diabetic patients without known CAD carry a risk approaching that of non-diabetics who have already had an MI. Risk factors are multiplicative, not merely additive — a smoker with hypertension and high cholesterol has far more than three times the baseline risk. Formal tools (QRISK, ASCVD, SCORE2) estimate 10-year risk to guide when to start statins and blood-pressure treatment.

Diagnosis: The ECG and Troponin

Two tools do most of the work in acute CAD.

The 12-lead ECG is fast, cheap, and decisive in the first minutes. Key patterns:

• ST elevation in two contiguous leads = STEMI until proven otherwise → immediate reperfusion pathway.
• ST depression / T-wave inversion = ischaemia, seen in NSTEMI/UA.
• New left bundle branch block with ischaemic symptoms is treated as a STEMI-equivalent.
• Lead groupings localise the culprit vessel: II, III, aVF = inferior (RCA); V1–V4 = anteroseptal (LAD); I, aVL, V5–V6 = lateral (circumflex). Later, pathological Q waves signal established infarction.

Cardiac troponin (troponin T or I) is the biomarker of myocyte death. Troponins are proteins of the cardiac contractile apparatus; when myocytes die, they leak into the blood. Modern high-sensitivity troponin assays detect tiny rises within 1–3 hours. The defining feature of MI (per the Universal Definition) is a rise and/or fall of troponin above the 99th percentile plus clinical evidence of ischaemia. A single value is less useful than a trend — this distinguishes acute infarction from the chronically raised troponin seen in kidney disease or heart failure. Troponin is exquisitely sensitive but not perfectly specific: it also rises in myocarditis, pulmonary embolism, sepsis, and tachyarrhythmia, so it must be read in context.

Supporting tests: CT coronary angiography and functional stress testing for stable, lower-risk patients; invasive coronary angiography (the catheter "gold standard") for high-risk ACS and to guide revascularisation; echocardiography for wall-motion abnormalities and complications.

Management: Prevention, Chronic Disease, and Acute Reperfusion

Chronic (stable) coronary disease aims to relieve symptoms and prevent events. The evidence-based backbone:

• Antiplatelet: lifelong low-dose aspirin (or clopidogrel).
• Statin: high-intensity statin to lower LDL and stabilise plaque — one of the biggest wins in all of medicine.
• Anti-anginals: beta-blockers (reduce heart rate and demand) first-line; add calcium-channel blockers, long-acting nitrates, or others as needed. GTN spray for acute episodes.
• Risk-factor control: stop smoking, treat hypertension and diabetes, ACE inhibitor if diabetic/hypertensive/reduced EF, diet and exercise, cardiac rehabilitation.
• Revascularisation (PCI or CABG) for symptoms refractory to medication or for prognostically important disease (e.g. significant left main or triple-vessel disease, where CABG often wins).

Acute coronary syndrome — immediate care. A useful memory aid is MONA-B (used judiciously, not rotely): Morphine for pain, Oxygen only if hypoxic, Nitrates, Aspirin, plus a Beta-blocker when safe. The two pillars are:

• Dual antiplatelet therapy: aspirin plus a P2Y12 inhibitor (ticagrelor, prasugrel, or clopidogrel), given early.
• Reperfusion for STEMI: primary PCI (angioplasty and stent) is first choice if achievable within ~120 minutes; otherwise thrombolysis (a fibrinolytic drug to dissolve the clot) followed by transfer. Anticoagulation (e.g. heparin) accompanies these.

For NSTEMI/UA, treatment is risk-stratified antithrombotic therapy with early invasive angiography (typically within 24–72 hours) for higher-risk patients, rather than immediate lysis (there is no acute total occlusion to bust).

Real-World Applications

• Primary care and prevention: cardiovascular risk scoring at routine checks decides who gets a statin — preventing MIs years before they would occur. Public-health smoking bans measurably cut MI admissions.
• Emergency medicine: the "chest pain pathway" — ECG within 10 minutes of arrival, serial high-sensitivity troponins — safely rules many patients in or out within a couple of hours, a huge operational efficiency.
• Everyday relevance: recognising that jaw, arm, or epigastric discomfort with sweating can be cardiac — especially in women, the elderly, and diabetics who often have atypical or silent presentations — saves lives. Knowing to chew aspirin and call emergency services during a suspected heart attack is genuinely life-saving public knowledge.

Common Mistakes

• "Only crushing left-sided chest pain is a heart attack." Wrong. Women, elderly, and diabetic patients frequently present atypically — with breathlessness, fatigue, nausea, epigastric pain, or no pain at all (silent MI). Relying on the textbook picture misses infarcts.
• "A normal ECG rules out a heart attack." Wrong. The initial ECG is normal or non-specific in a substantial minority of NSTEMIs and even some early STEMIs. That is why we take serial ECGs and troponins, not a single snapshot.
• "The tightest narrowing is the one that will cause the heart attack." Wrong. Most infarcts arise from rupture of moderate, lipid-rich vulnerable plaques, not the tightest stenoses. This is why plaque-stabilising statins and risk-factor control matter more than chasing every narrowing with a stent, and why stenting stable lesions does not reduce mortality the way treating risk factors does.
• "A raised troponin always means a heart attack." Wrong. Troponin marks myocyte injury, not its cause. Kidney failure, sepsis, PE, myocarditis, and tachyarrhythmias raise it too. The clinical context and the rise-and-fall pattern make the diagnosis.

Comparison and Connections

Feature	Stable Angina	Unstable Angina	NSTEMI	STEMI
Trigger	Exertion	Rest or crescendo	Rest	Rest
Coronary lesion	Fixed narrowing	Partial thrombus	Partial/transient occlusion	Complete occlusion
ECG	Usually normal at rest	ST depression / T inversion	ST depression / T inversion	ST elevation
Troponin	Normal	Normal	Raised	Raised
Myocardium dies?	No	No	Yes (subendocardial)	Yes (transmural)
Priority	Elective work-up	Urgent	Urgent, early invasive	Emergency reperfusion

CAD connects tightly to heart failure (infarcted muscle weakens the pump), arrhythmias (ischaemia triggers ventricular fibrillation — the usual cause of sudden cardiac death), and the shared risk-factor world of stroke and peripheral arterial disease, which are the same atherosclerotic process in different vessels.

Practice Questions

Recall

Q: What ECG change defines a STEMI, and what does it imply about the artery? A: ST-segment elevation in two contiguous leads. It implies complete, persistent occlusion of a coronary artery causing transmural ischaemia — an indication for immediate reperfusion.

Understanding

Q: Why can a plaque causing only 40% stenosis be more dangerous than one causing 80%? A: Because acute events are driven by plaque rupture and thrombosis, not just narrowing. A "vulnerable" plaque with a thin fibrous cap and large lipid core can rupture and cause total occlusion, even if it narrows the lumen modestly. The 80% stable plaque with a thick cap causes predictable angina but is less likely to rupture.

Application

Q: A 62-year-old presents with 40 minutes of rest chest pain. ECG shows ST depression in V4–V6. First troponin is normal. What is the likely diagnosis and next step? A: Likely ACS — unstable angina or evolving NSTEMI. The normal first troponin does not exclude it. Give aspirin plus a P2Y12 inhibitor and anticoagulation, treat pain, and repeat troponin (high-sensitivity) at 1–3 hours; a rise confirms NSTEMI and prompts early invasive angiography.

Analysis

Q: Explain how DeWood's 1980 angiographic study confirmed Herrick's 1912 theory and why this changed treatment. A: DeWood showed that most patients in the first hours of transmural MI had a totally occluded coronary artery containing fresh thrombus, and that occlusion decreased over subsequent hours. This directly confirmed Herrick's claim that acute thrombosis on diseased artery causes MI (and that patients survive it). Because a clot is the proximate cause, therapies that remove or dissolve it early — thrombolysis and primary PCI — could interrupt the infarct, transforming MI from a fatalistically managed event into a time-critical, treatable emergency.

FAQ

Is angina the same as a heart attack? No. Angina is reversible ischaemia — chest discomfort from inadequate blood supply, with no muscle death (troponin normal). A heart attack (MI) involves actual myocyte death from occlusion, with raised troponin. Stable angina can, however, be the warning sign before an MI.

Why is aspirin given during a suspected heart attack? Aspirin blocks platelet aggregation, limiting growth of the thrombus that is occluding the artery. Given early in ACS, it measurably reduces mortality — which is why chewing 300 mg while awaiting help is standard advice.

Can young, fit people get CAD? Yes, though less commonly. Genetic conditions like familial hypercholesterolaemia, heavy smoking, cocaine use, and strong family history can cause premature CAD. Fatty streaks begin in adolescence in everyone; lifestyle and genes determine how fast they progress.

What is the difference between a stent (PCI) and bypass (CABG)? PCI threads a catheter to the blockage and props the artery open with a stent — minimally invasive, ideal for acute STEMI and focal disease. CABG is open surgery grafting a vessel around blockages, often better for complex multi-vessel or left-main disease and in diabetics.

Why do I need statins if my cholesterol is "normal"? After CAD is diagnosed, statins are given not just to lower LDL but to stabilise plaque and reduce inflammation, cutting future events even when baseline cholesterol looks unremarkable. The benefit is in event prevention, not the number alone.

Are women's heart attacks different? Often, yes. Women more frequently have atypical symptoms (fatigue, breathlessness, nausea, back or jaw pain), present later, and are under-treated. Awareness of this reduces missed diagnoses.

Quick Revision

• CAD = atherosclerotic narrowing of coronary arteries; a chronic inflammatory, lipid-driven disease.
• Fatty streak → atheroma → vulnerable plaque rupture → thrombosis → ACS.
• Stable angina: exertional, relieved by rest/GTN, troponin normal.
• ACS spectrum: UA (troponin normal) → NSTEMI (troponin up, no ST elevation) → STEMI (ST elevation, total occlusion).
• Diagnosis: ECG (ST elevation/depression, lead localisation) + serial high-sensitivity troponin (rise and fall).
• STEMI = emergency: primary PCI within ~120 min or thrombolysis. "Time is muscle."
• Backbone therapy: aspirin + P2Y12 inhibitor, high-intensity statin, beta-blocker/ACE inhibitor, aggressive risk-factor control.
• History: Heberden (angina, 1768) → Herrick (thrombosis theory, 1912) → DeWood (angiographic proof, 1980).

Related Topics

Prerequisites

• Cardiology overview
• Cardiovascular physiology (see ../../2._Physiology/index.md)

Related Topics

• Pharmacology of antiplatelets, statins, and nitrates (see ../../5._Pharmacology/index.md)
• Pathology of atherosclerosis (see ../../4._Pathology/index.md)

Next Topics

• Heart failure and its ischaemic causes
• Cardiac arrhythmias and sudden cardiac death (see ../../23._Emergency_Medicine/index.md)