Cardiomyopathies
- Cardiomyopathy means the heart muscle itself is sick — not the coronary arteries, not the valves, the muscle.
- Sort them by shape and behavior: dilated (a stretched-out balloon), hypertrophic (a too-thick wall), and restrictive (a stiff, won't-relax wall).
- Cardiac MRI is the star here — it measures function and shows tissue character with late gadolinium enhancement (LGE).
- The pattern of scar on LGE is the secret decoder ring: where it sits often tells you the cause.
- Your first job is always to rule out plain old coronary artery disease before blaming the muscle.
Think of the heart as an engine. Most cardiac trouble is a fuel-line problem (blocked coronary arteries) or a valve problem (leaky doors). Cardiomyopathy is different: the engine block itself is faulty. The pump is intact in plumbing terms, but the meat of it is too floppy, too thick, or too stiff to do its job. That's the whole family in one sentence.
Sorting the family by shape
Radiologists are deeply visual creatures, so we group these by what the muscle looks like and how it moves. Three classic shapes get you most of the way.
| Type | The muscle problem | Memorable image |
|---|---|---|
| Dilated | Thin-walled, weak, poor squeeze | A balloon left blown up too long — stretched, saggy, can't recoil |
| Hypertrophic | Wall too thick, often lopsided | A weightlifter's bicep crammed into a small sleeve |
| Restrictive | Wall stiff, won't relax to fill | A waterlogged sponge that won't expand to soak up more |
The catch is that these are shapes, not diagnoses. Plenty of different diseases funnel into the same shape, which is exactly why tissue characterization matters so much.
Dilated: the saggy balloon
Dilated cardiomyopathy is the floppy one. The left ventricle blows up, the walls thin out, and the squeeze (ejection fraction) drops. On a chest radiograph you may just see a big globular heart and, when it decompensates, signs of pulmonary edema — the lungs getting waterlogged because the failing pump backs fluid up behind it.
The crucial fork in the road: is this from old heart attacks (ischemic) or not? That distinction changes everything about treatment, and it's the reason we image.
Before calling a dilated heart a "cardiomyopathy," you have to exclude ischemic disease. A heart wrecked by multiple infarcts looks dilated and weak too — but that's coronary disease wearing the costume, not a primary muscle disorder.
Hypertrophic: the over-built wall
Here the muscle is too thick, classically the septum (the wall between the two ventricles) more than the rest. That asymmetry is the tell. The thickened muscle can crowd the outflow tract — imagine a doorway half-bricked-up — and obstruct blood leaving the heart.
Restrictive: the stiff wall
This is the sneaky one. The wall may not look dramatically thick or dilated, but it's stiff — it won't relax to let blood fill in. The chambers fill poorly, and pressure backs up. Because the geometry can look almost normal, restrictive disease is easy to underestimate by eye. The infiltrating diseases that cause it — abnormal proteins or other material packed into the muscle — often leave fingerprints that MRI can read even when the shape looks unremarkable.
Why MRI is the hero
Echocardiography is usually first through the door, and it's great for function. But cardiac MRI does the thing nothing else does well: it tells you what the muscle is made of.
The key trick is late gadolinium enhancement (LGE). Give contrast, wait several minutes, and it lingers in scarred or abnormal tissue while washing out of healthy muscle. So scar lights up bright against dark normal myocardium. Better yet, the location and pattern of that bright scar is a clue to the cause.
LGE pattern is the decoder ring. Scar that follows a coronary artery territory and reaches the inner lining (subendocardial) points to old infarction. Scar that ignores coronary territories — patchy in the mid-wall, or hugging the outer surface — points toward a primary muscle disease instead.
The trap worth naming
A subtly enlarged, hard-working heart can look like a cardiomyopathy when it's really just responding to something else — long-standing high blood pressure, an athlete's normal adaptation, or an unrecognized valve problem. Always ask whether the muscle is sick on its own or simply reacting to a load placed on it. And don't confuse muscle disease with the sac around it — pericardial disease can mimic the restrictive picture clinically while the muscle itself is fine.
Putting it together
When you meet a cardiomyopathy, walk the same path every time. First, what shape is the heart — dilated, hypertrophic, or restrictive? Second, is this just coronary disease in disguise? Third, what does the tissue tell you on MRI, and where does the scar sit?
The single most useful question in this whole topic: "Does the scar respect coronary territories or not?" Answer that, and you've usually separated a plumbing problem from a true engine-block problem — which is the entire point of imaging these patients.
Get the shape, exclude the arteries, then let the tissue talk. That's the muscle, demystified.