Reading the echo report — between 5 mm and 6 mm
After the echocardiogram you are handed a report dense with letters and numbers: IVSd 6.2, LVPWd 5.8, LA/Ao 1.7, FS 45%… You heard the explanation in the consult room, but back home, it is hard to tell which numbers actually matter.
This article is the map for that report. The numbers that truly matter in HCM are fewer than you would think — two wall thicknesses, one left-atrium ratio, and three risk findings. Read those and the rest of the page is background.
One line — wall thickness (IVSd·LVPWd) answers "is there disease"; the left atrium (LA/Ao) answers "how dangerous"; SAM, smoke and appendage velocity answer "what to watch right now". Read every recheck in that order.
1. The map — what to find on the page
| On the report | What it is | The question it answers |
|---|---|---|
| IVSd | Interventricular septum thickness, diastole | Is there disease (section 2) |
| LVPWd | Left ventricular free wall thickness, diastole | |
| LA/Ao (or LA:Ao) | Left atrium size ÷ aorta size | How dangerous (section 4) |
| SAM / LVOT | The mitral valve swinging into the outflow tract | What to watch now (section 5) |
| SEC / smoke | "Smoke" inside the atrium — blood is stagnating | |
| LAA velocity | Blood speed in the atrial appendage | |
| FS%, E/A etc. | Systolic/diastolic function indices | Supporting detail — your vet's territory |
One letter matters enormously: the lowercase d after a thickness means diastole (relaxed); s means systole. HCM is judged only on the thickness at the heart's most relaxed, thinnest moment (d) — systolic values are thick even in normal hearts, so do not be alarmed by them.
2. Wall thickness — the 6 mm line, and the space between 5 and 6
| Diastolic wall thickness (max of IVSd / LVPWd) | Reading (ACVIM 2020) |
|---|---|
| Under 5 mm | Normal |
| 5 – 6 mm | Equivocal (grey zone) — judgement deferred, follow up |
| 6 mm and above | HCM phenotype — after excluding the causes in section 3 |
| 9 mm and above | Severe hypertrophy — a prognostic factor |
- The single thickest segment decides — HCM often thickens patches of wall rather than the whole wall evenly ("6.5 mm at the basal septum only"). That is why reports may list several regional measurements
- Body size matters — the same 6 mm yardstick is imperfect for a 2 kg cat and a 7 kg cat. For borderline values you may hear about weight-normalised measurements; that is a sign of careful work, not confusion
- "Equivocal" is not a diagnosis — many cats in the 5–6 mm zone never progress. The correct prescription for a grey-zone result is not a drug but a recheck in 6–12 months
3. Other reasons walls look thick — it may not be HCM
| Cause | Why walls look thick | How it is separated |
|---|---|---|
| Dehydration (pseudohypertrophy) | An under-filled ventricle makes the empty walls look relatively thick — healthy cats have measured above 5.5 mm when volume-depleted | Rescan after rehydration |
| Hyperthyroidism | Genuinely thickens the myocardium | T4 test — can improve with treatment |
| Hypertension | Walls bulk up against high pressure | Blood pressure — can improve with control |
| Transient myocardial thickening (TMT) | Temporary thickening after anaesthesia, trauma or systemic illness that reverses over months — especially in young cats | Time — if a rescan at 2–6 months shows thinning, it was never HCM |
| Infiltrative disease (e.g. lymphoma) | Other tissue invading the muscle | Rare — specialist territory |
Especially if a young cat was called "thick-walled" right after being ill (anaesthesia, an accident, severe sickness), ask about transient myocardial thickening. There are real cases where the recheck months later is normal and the HCM diagnosis is withdrawn. This is why one first echo never fixes a lifelong label.
4. The left atrium (LA/Ao) — this disease's risk gauge
As the diagnosis-day article said: the fork is not the wall but the atrium. Blood that cannot enter the stiff ventricle backs up into the left atrium; the larger it stretches, the closer the cat stands to heart failure (fluid) and clots (stagnant blood congealing).
| LA/Ao (2D short-axis) | Reading | Direction of response |
|---|---|---|
| Below ~1.5–1.6 | Normal size — toward B1 | Monitor (recheck 6–12 months) |
| ~1.6 – 1.8 | Grey zone of mild-to-moderate enlargement | Shorter recheck interval, watch the trend |
| Roughly 1.9 and above | Moderate or worse enlargement — toward B2 | Discuss clopidogrel; recheck 3–6 months |
One caution — LA/Ao values from different methods (2D short-axis vs M-mode) are not interchangeable. If this report's LA/Ao differs from the last one, first ask whether the heart changed or the measuring method did. Tracking belongs at the same clinic, by the same method.
5. The three risk findings — their presence changes the plan
- SAM (systolic anterior motion) — the mitral valve gets dragged into the outflow tract during contraction, narrowing the exit. Present in 30–50% of HCM cats and the main source of murmurs. It sounds frightening, but SAM by itself does not mean a bad prognosis, and it can appear or disappear over the years. When severe, a heart-rate-slowing drug (atenolol) may be considered
- Spontaneous echo contrast (SEC, "smoke") — a swirling haze inside the left atrium. It means blood is stagnating on the verge of clotting — the strongest precursor of a thrombus. If this word is on the report, clopidogrel moves from "discuss" toward "essential"
- Low left atrial appendage (LAA) velocity — blood speed in the atrium's pouch-like corner. The slower it flows (roughly below 0.25 m/s), the more stagnant the blood — the same message as smoke
In short: section 4's atrial size is the total of risk; these three findings are what is happening right now. From the moment smoke or low velocity appears, clot prevention becomes the centre of care — read alongside the blood-side signals in NLR and PNR.
6. The blood tests beside the echo — NT-proBNP and troponin
- NT-proBNP — released when heart muscle is stretched. On the quantitative test, above 100 pmol/L suggests heart disease and justifies an echo; above 270 pmol/L in a breathless cat strongly supports the heart as the cause. The in-clinic SNAP version is a normal/abnormal screen only
- Troponin I (cTnI) — a protein leaking from damaged heart-muscle cells. Higher means active injury; as a trend it also helps judge the effect of treatment or diet interventions
Neither replaces the echocardiogram — they are the bridge between echoes, and the signal for moving the next one up.
7. Comparing rechecks — two reports side by side
- Track three numbers — maximum wall thickness (mm) · LA/Ao · presence of risk findings (SAM/smoke/velocity). Logged with dates in the app, they answer the only question that matters next time: "is it growing?"
- 0.5 mm of change may be no change — echo measurements sway with the operator, the angle, the day's heart rate. Treat ±0.5 mm of wall or ±0.1–0.2 of LA/Ao as noise, and call it a trend only when the direction repeats twice
- Same clinic, ideally same hands — machines and measurers change the numbers. If you switch hospitals, bring the previous reports (images if possible)
- Note sedation — sedatives shift heart rate and flow, affecting some values. Whether it was used, this time and last time, is part of the comparison
8. What to ask your vet
- "How thick was the thickest spot, and which segment was it?"
- "What was the LA/Ao, and by which method (2D or M-mode)? Same as last time?"
- "Was there SAM or smoke? Was the appendage velocity measured?"
- "Were dehydration, thyroid and blood pressure excluded? (If young) could this be transient thickening?"
- "So is my cat B1 or B2 — and when is the next echo?"
- "May I have a copy of the report, ideally with the full measurement table?"
9. Related
- The day of diagnosis — why the stage splits on the left atrium
- NLR and PNR — the blood-side risk signals between echoes
- Resting respiratory rate — the worse the report, the more this number matters
- The HCM Bible — contents
One line — from the report, keep only the maximum wall thickness, the LA/Ao, and the three risk findings.
The wall names the disease, the atrium sizes the danger, and the smoke sets today's to-do list.