Pimobendan is a relatively new drug here in the United States, but it is rapidly becoming a standard part of treating congestive heart failure (CHF) resulting from some types of heart disease in dogs. Little research has been done into its potential usefulness in cats, however, so I was glad to see an article addressing just this question in a recent issue of the Journal of the American Veterinary Medical Association (JAVMA).
Part of the reason for the relative lack of interest in studying pimobendan in cats has to do with the type of heart disease that cats are diagnosed with most frequently — hypertrophic cardiomyopathy (HCM). HCM involves a thickening of the muscles in part of the heart (the left ventricle), which prevents this chamber from filling with a normal amount of blood. Therefore when the left ventricle contracts, an inadequate volume of blood is pushed out into the body and blood can “back up” in the lungs.
Pimobendan is a positive inotrope. This type of drug causes heart muscle to contract more strongly, which has traditionally not been thought of as what a cat with HCM needs. But pimobendan has other effects as well, including an ability to widen the channels (arteries and veins) through which blood flows and decrease the formation of blood clots. The authors of the JAVMA paper hypothesized that the benefits of adding pimobendan to standard HCM treatment would outweigh the risks and lead to an improvement in survival times.
The researchers tested this hypothesis by looking at the medical records of 54 cats with congestive heart failure caused by HCM or a related condition called hypertrophic obstructive cardiomyopathy (HOCM). Twenty-seven of the cats received pimobendan as a part of their treatment (case cats) and 27 did not (control cats). The control cats were chosen in such a way as to match the case cats “on the basis of age, sex, body weight, type of cardiomyopathy, and manifestation of CHF.” The study revealed:
Addition of pimobendan to standard treatment regimens for cats with CHF secondary to HCM or HOCM appeared to confer a clear benefit in survival time … Furthermore, pimobendan was tolerated well by cats with CHF secondary to HCM and HOCM, and no additional adverse effects were noted in case versus control cats enrolled in the study.
The effect of pimobendan was quite remarkable. The median survival time of the cats who received the drug was 626 days and only 103 days for those who did not — a greater than 6-fold difference.
This is a small study that does not answer all questions regarding the safety and efficacy of using pimobendan in cats, but it certainly offers new hope to veterinarians and owners who are treating cats with congestive heart failure secondary to hypertrophic cardiomyopathy.
Dr. Jennifer Coates
Case-control study of the effects of pimobendan on survival time in cats with hypertrophic cardiomyopathy and congestive heart failure. Reina-Doreste Y, Stern JA, Keene BW, Tou SP, Atkins CE, DeFrancesco TC, Ames MK, Hodge TE, Meurs KM. J Am Vet Med Assoc. 2014 Sep 1;245(5):534-9.