Cardiac amyloidosis — an infiltrative cardiomyopathy

MRI · Nuclear

First and second year — the floor first, then every step

Thick walls with a small cavity, diffuse subendocardial or transmural LGE, myocardium that will not null, very high native T1 and ECV — then bone-avid tracer scintigraphy and a light-chain screen to separate ATTR from AL.

Orient first

Amyloid expands the extracellular space: walls thicken without true hypertrophy, the atria enlarge, and ECG voltage is low for the wall thickness.
Gadolinium is taken up by the infiltrated myocardium, so blood pool and myocardium null at similar inversion times — the TI scout shows it.
Two main types: AL (light chain, haematological, urgent) and ATTR (wild-type or hereditary). Bone-avid scintigraphy grade 2–3 WITHOUT a monoclonal protein diagnoses ATTR non-invasively.

Acquire the study

Cine SSFP short-axis stack and long axes; native T1 mapping; TI scout (Look-Locker) before LGE; LGE with PSIR; post-contrast T1 mapping for ECV (needs a same-day haematocrit).

The manoeuvre

Cine: concentric LV thickening (often RV and atrial septum too), small cavity, preserved EF early, biatrial enlargement, small pericardial and pleural effusions.
TI scout: myocardium nulls BEFORE or WITH the blood pool — abnormal gadolinium kinetics.
LGE (PSIR): diffuse global subendocardial enhancement not in a coronary territory, progressing to transmural; atrial wall enhancement.
Mapping: markedly raised native T1; ECV very high (often > 40% — verify local range).

What confirms it

Typical CMR (diffuse subendocardial/transmural LGE, abnormal nulling, high T1/ECV) plus grade 2–3 bone-tracer uptake on SPECT with no monoclonal protein (ATTR); AL needs tissue.

What licenses you to exclude it

Normal native T1 and ECV with no LGE make cardiac amyloidosis very unlikely.

The classic misread

Using magnitude-only LGE with a nulling TI chosen from "normal" myocardium — the whole heart looks dark or uniformly grey and the diagnosis is missed.

Reference values

Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.

Normal limits

Left ventricle · End-diastolic wall thickness, normal adult
commonly around 6–10 mm at end-diastole in a non-athletic adult; 11–12 mm is a grey zone and 15 mm is the HCM conversation (see that entry)
Must be end-diastole and perpendicular to the wall. This entry is the NORMAL range; the HCM entry is the diagnostic threshold — do not collapse them.
CT · MRI

Diagnostic criteria

Left ventricle · End-diastolic wall thickness for hypertrophic cardiomyopathy
a wall thickness of 15 mm or more in any segment (13 mm or more with a family history or positive genotype) meets the conventional HCM criterion in adults
Must be measured at END-DIASTOLE perpendicular to the wall — an oblique or systolic measurement over-reads. Hypertensive heart disease and athletic remodelling overlap the 13–15 mm range; the pattern of hypertrophy and the clinical context decide. Versioned criterion — verify against the current edition before clinical use.
MRI · CT