Spontaneous echo contrast (smoke) in the feline left atrium
7-year-old Ragdoll with no clinical signs, referred for a murmur and gallop rhythm. Echocardiography: LV hypertrophy of 7.5 mm, left atrium of 21 mm (LA/Ao 2.0), reduced left auricular velocity and a slow swirling echogenic pattern inside the atrium. No effusions or oedema on radiographs.
Which interpretation is correct?
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A. Stage B2; the smoke indicates blood stasis and a high risk of thromboembolism, so thromboprophylaxis is indicated
Correct. Spontaneous echo contrast reflects cell aggregation due to slow flow. Together with an enlarged atrium and low auricular velocity, the 2020 ACVIM consensus recommends thromboprophylaxis (clopidogrel) even in an asymptomatic cat.
B. It is an artefact from excessive gain with no clinical significance
Excessive gain affects the whole image. A slow swirl confined to an enlarged atrium is a real finding with a poor prognosis; adjust the gain and confirm it, do not ignore it.
C. Stage C: smoke equals a thrombus and thromboembolism has already occurred
Smoke is a prothrombotic state, not an organised thrombus, and stage C requires CHF or clinical thromboembolism. This cat remains in stage B2.
D. It heralds imminent pulmonary oedema: start preventive furosemide
Diuretics are only indicated when there is congestion. In a cat without oedema or effusions they bring no benefit and cause dehydration and azotaemia.
lightbulb Key takeaway
Always look for smoke, thrombi and left auricular velocity in cats with an enlarged atrium: they are the markers of thromboembolic risk. Stage B2 in cats changes management: thromboprophylaxis and home monitoring of respiratory rate.
References: ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats (2020)
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.