Coronary Artery Disease
- Coronary artery disease (CAD) is plaque slowly narrowing the heart's own supply pipes — the coronary arteries that feed the heart muscle itself.
- Imaging answers two different questions: Is there plaque, and how much? (anatomy) and Is any of it actually starving muscle? (function/ischemia).
- Coronary CT angiography is the great gatekeeper: it's extremely good at telling you the arteries are clean, which rules CAD out in one shot.
- A calcium score is a cheap, no-contrast peek at how much calcified plaque has built up — a number that tracks your long-term risk.
- The whole point of imaging is to catch trouble before it becomes a heart attack, not to admire it afterward.
The heart is a tireless little pump, and like any pump it needs its own fuel line. That fuel line is the coronary arteries — three main hoses draped over the outside of the heart, feeding the very muscle that's doing the squeezing. Coronary artery disease (CAD) is the slow, sneaky process of gunk building up inside those hoses until the flow gets pinched. Think of the limescale that creeps along the inside of an old kettle, except this kettle is keeping you alive.
What's actually happening in the pipe
The gunk is atherosclerotic plaque — a mix of cholesterol, inflammatory cells, and eventually calcium, building up in the artery wall. Early on the wall politely bulges outward to make room, so the channel stays open and you feel nothing. That's the cruel part: the disease is well underway long before anything hurts.
Trouble arrives one of two ways. The plaque can grow inward until it strangles the channel and the muscle downstream goes hungry whenever you ask it to work harder (that's stable angina — chest pain that shows up walking uphill and quits when you rest). Or a plaque can suddenly crack open, the body slaps a clot over the crack like a scab, and the pipe slams shut in minutes. That's the heart attack.
A key mind-bender: the plaque most likely to kill you isn't always the biggest one. A modest-looking plaque with a thin, inflamed cap can rupture, while a bulky, heavily calcified one sits there stable for years. Size of the blockage and danger of the blockage are related but not the same question.
The two questions imaging answers
Every cardiac imaging test for CAD is really chasing one of two questions — is there plaque? and does it matter? — and it helps enormously to know which one you're asking. (One of them, plaque burden, is just an anatomy question asked a slightly different way.)
| Question | What it means | Who answers it |
|---|---|---|
| Anatomy | Is there plaque, where, and how tight? | Coronary CT angiography; invasive catheter angiography |
| Burden | How much calcified plaque has built up overall? | Calcium score (non-contrast CT) |
| Function | Is a narrowing actually starving muscle? | Stress testing — stress MRI, nuclear perfusion, stress echo |
Anatomy tells you the pipe looks narrow. Function tells you whether that narrowing matters to the muscle behind it. A 60% narrowing might be doing nothing, or it might be the cause of someone's chest pain — you often can't tell from the picture alone, which is why these tests are partners, not rivals.
The calcium score: a number you can hand a patient
The simplest test is the coronary calcium score, a quick CT with no contrast and barely any radiation. Calcium in a coronary wall only exists because plaque put it there, so the scanner tallies it up into a single number. Zero is genuinely reassuring. A high number means a lot of plaque has accumulated over the years, which nudges your long-term risk up and often the conversation toward prevention. It's like counting the rust spots on a car bumper — not a diagnosis of a breakdown, but an honest read on the wear and tear.
CCTA: the great rule-out
When someone shows up with chest pain that could be cardiac but probably isn't, the star of the show is coronary CT angiography (CCTA) — a contrast CT timed to light up the coronary arteries themselves. Its superpower is the negative scan: if CCTA shows clean, wide-open arteries, the chance that CAD is behind the symptoms is very low, and you can confidently send the patient home looking elsewhere. Few tests in medicine rule a disease out this convincingly.
When CCTA does find narrowing, the picture is read against the coronary anatomy — naming which vessel and grading how tight, usually in plain "mild / moderate / severe" terms. A tight or worrying lesion may then earn a trip to the catheter lab or a stress test to see if it's actually starving muscle.
Heavy calcium is CCTA's nemesis. Dense calcified plaque "blooms" — it glares so brightly it spills over and looks bigger than it is, hiding the actual lumen behind it. So in a heavily calcified artery, CCTA tends to overcall how tight the narrowing is. The very thing the calcium score measures is the thing that can blur the angiogram.
When the muscle has already paid the price
If a coronary has been blocked long enough, the muscle it fed dies and turns to scar. Cardiac MRI is the referee here: a contrast technique called late gadolinium enhancement makes scar light up brightly, and the pattern of that brightness tells the story. Scar from a coronary blockage starts at the inner lining of the heart wall — the layer that's farthest from the blood supply and starves first — which neatly distinguishes a heart attack's scar from the scarring of non-coronary heart muscle diseases.
Don't confuse CAD with the aorta's own emergencies. Tearing chest pain ripping to the back is a different beast entirely — that's acute aortic syndrome, and it lives next door, not here.
The throughline for all of it: imaging exists to find the limescale in the kettle while it's still just limescale. Catch the plaque, gauge whether it matters, and act before the pipe ever slams shut.