Pimobendan in cats with outflow tract obstruction

Question

7-year-old domestic shorthair cat stabilised after an episode of pulmonary oedema. Echocardiography: concentric LV hypertrophy, systolic anterior motion of the mitral valve (SAM) with a 70 mmHg dynamic outflow tract gradient and a moderately dilated left atrium.

Which statement about treatment is correct?

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A. Furosemide is contraindicated because reducing preload worsens the obstruction

Excessive preload reduction can accentuate dynamic obstruction, but with congestive heart failure a diuretic is essential. It is used at the lowest effective dose.

B. Clopidogrel is not indicated because the cat has not had a thromboembolism

The 2020 ACVIM feline cardiomyopathy consensus recommends thromboprophylaxis in cats with a dilated left atrium or heart failure, even without a previous episode.

C. Pimobendan is indicated to improve contractility and filling

In HCM contractility is preserved or increased; the problem is diastolic dysfunction. Increasing contractility in the presence of SAM may raise the gradient.

D. Pimobendan is best avoided: its positive inotropic and vasodilator effects may worsen the dynamic obstruction

Correct. Pimobendan is an inodilator (it sensitises troponin C to calcium and inhibits phosphodiesterase 3). Greater contractility and lower afterload reduce systolic cavity size and promote SAM, which may raise the gradient and cause hypotension.

lightbulb Key takeaway

In cats with heart failure without outflow tract obstruction (e.g. end-stage HCM with systolic dysfunction or restrictive cardiomyopathy), pimobendan may be considered off-label. Before prescribing it to a cat, confirm by echocardiography that there is no SAM or significant gradient.

Which statement about treatment is correct?

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