Summarised by Dr Marlies Bohm BVSc DSAM, MMedVet(Med), DipECVIM.
Why they did it
Pimobendan has been shown to improve survival time in dogs with dilated cardiomyopathy (DCM) and myxomatous valvular degeneration by improving systolic function and acting as a balanced vasodilator. It also has anti-platelet properties. Pimobendan has been used in cats with a variety of cardiac diseases but there is a theoretical concern that this drug could worsen the dynamic left ventricular outflow tract obstruction (LVOTO) that is observed in some cats with hypertrophic cardiomyopathy (HCM). Dynamic LVOTO develops when the section of interventricular septum just under the aorta hypertrophies and / or when the anterior mitral valve leaflet is sucked into the outflow tract just under the aorta during systole. This means that the hole through which the blood leaves the ventricle is narrowed resulting in turbulent blood flow in the aorta, an audible murmur and increased work for the LV myocardium to empty blood out of the chamber through this narrowed exit. If Pimobendan increases the LVOTO, its use could accelerate the progression of HCM by encouraging myocardial hypertrophy and could potentially decrease cardiac output. In addition, cats with HCM have normal systolic function so shouldn’t really need inotropic support.
What they did:
They identified 2 groups of 27 cats retrospectively. All had HCM and 5 in each group had dynamic LVOTO. All were in congestive heart failure (CHF) at the start of treatment. They were matched according to age and weight. Cats with fixed outflow tract obstruction were excluded. All were treated with frusemide and most with an ACEI (24/27 in each group). More control cats received atenolol (9/27 vs 3/27) while more pimobendan treated cats received anticoagulant treatment (25/27 vs 19/27 in the control group). Pimobendan dose was 0.15 – 1.0 mg/kg/d in 2-3 divided doses.
What they found
The median survival time (date at which the 14th cat in each group died or was ethanased aro cardiac disease) was 626 days in the group treated with pimobendan and 103 days in the control cats. There were too few cats with LVOTO to come to any firm conclusions about the effect of pimobendan in this subset of cats.
Take home message
Pimobendan does not seem to be harmful to cats with HCM and CHF. There may be a survival benefit in using pimobendan in cats with HCM. Ideally, this should be confirmed with a prospective study performed in a larger group of cats.