Abstract
Background: Pimobendan has been shown to impart a significant survival benefit in cardiomyopathic cats who receive it as part of heart failure therapy. However, use of pimobendan remains controversial in cats with hypertrophic cardiomyopathy (HCM) due to lack of pharmacodynamic data for pimobendan in cats with HCM and due to theoretical concerns for exacerbating left ventricular outflow tract obstructions.Hypothesis/Objectives: Our objective was to investigate the cardiac effects of pimobendan in cats with HCM. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function.Animals: Thirteen purpose-bred cats were studied from a research colony with naturally-occurring HCM due to a variant in myosin binding protein C.Methods: Cats underwent two examinations 24 h apart with complete standard echocardiography. On their first day of evaluation, they were randomized to receive oral placebo or 1.25 mg pimobendan 1 h prior to exam. On their second examination, they were crossed over and received the remaining treatment. Investigators were blinded to all treatments.Results: The pimobendan group had a significant increase in left atrial fractional shortening (pimobendan group 41.7% ± 5.9; placebo group 36.1% ± 6.0; p = 0.04). There was no significant difference in left ventricular outflow tract (LVOT) velocities between the groups (pimobendan group 2.8 m/s ± 0.8; placebo group 2.6 m/s ± 1.0). There were no significant differences between the number of cats with LVOT obstructions between groups (12 in pimobendan group; 11 in placebo group; p = 1.00). There were no detectable differences in any systolic measures, including left ventricular fractional shortening, mitral annular plane systolic excursion, and tricuspid annular plane systolic excursion. Doppler-based diastolic function assessment was precluded by persistent tachycardia.Conclusions: Improved left atrial function in the pimobendan group could explain some of the reported survival benefit for HCM cats in CHF. Pimobendan did not exacerbate LVOT obstructions and thus may not be contraindicated in HCM cats with LVOT obstructions. Future studies are needed to better characterize other physiologic effects, particularly regarding diastolic function assessment, and to better assess safety of pimobendan over a longer time-course.
Highlights
Pimobendan is a benzimidazole pyridazinone drug that has shown tremendous benefit in treatment of both canine congestive heart failure (CHF), pre-clinical dilated cardiomyopathy and preclinical degenerative valve disease [1,2,3,4,5,6]
47.5–67% of Hypertrophic cardiomyopathy (HCM) cats presenting to referral hospitals have concurrent left ventricular outflow tract obstructions (LVOTO) [9, 10]
There was no significant difference in heart rate (HR), left atrial (LA) size, and segmental wall thickness between the two treatment groups (Table 1)
Summary
Pimobendan is a benzimidazole pyridazinone drug that has shown tremendous benefit in treatment of both canine congestive heart failure (CHF), pre-clinical dilated cardiomyopathy and preclinical degenerative valve disease [1,2,3,4,5,6]. The positive effects in prolonging survival times, improving quality of life, and prolonging time to the development of CHF in dogs is unequivocal [2,3,4,5,6] This benefit is not universally accepted or characterized in feline cardiac disease. 47.5–67% of HCM cats presenting to referral hospitals have concurrent left ventricular outflow tract obstructions (LVOTO) [9, 10]. These obstructions can be secondary to several etiologies including systolic anterior motion of the anterior mitral leaflet (SAM), asymmetric septal hypertrophy, or a dynamic midventricular obstruction lesion caused by mid-ventricular and/or papillary muscle hypertrophy. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function.
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