The fundamentals of treating congestive heart failure in dogs and cats have not changed appreciably over the years, but one fairly new drug along with fairly new diagnostic tests have given veterinarians additional tools for patient care.
Pimobendan, marketed under the trade name Vetmedin by Boehringer Ingelheim Vetmedica of St. Joseph, Mo., is used in dogs with congestive heart failure secondary to dilated cardiomyopathy, chronic mitral valve insufficiency and degenerative mitral valve disease.
The drug increases heart muscle contractions and dilates the blood vessels, so as to strengthen the heart’s ability to pump and allow easier blood flow.
The Cardiocare test, manufactured by Idexx Laboratories of Westbrook, Maine, helps determine whether an animal’s labored breathing is caused by primary respiratory disease or congestive heart failure. The test measures a hormone released in the bloodstream in response to increased stretch or strain of heart muscle. A similar test was developed by Antech Diagnostics of Irvine, Calif.
The standard of care for canine congestive heart failure treatment, written by a committee of American College of Veterinary Internal Medicine cardiology diplomates, calls for triple therapy including furosemide, an angiotensin-converting enzyme (ACE) inhibitor, and pimobendan, noted Kristin MacDonald, DVM, Ph.D., Dipl. ACVIM (cardiology).
Speaking at the 2011 Canine Medicine Symposium, Dr. MacDonald said pimobendan increases cardiac efficiency without increasing myocardial oxygen consumption. Several scientific studies concluded that pimobendan appeared to increase survival time in heart failure patients.
The drug is a phosphodiesterase inhibitor licensed for use in dogs with heart failure in the United States, Canada, Europe and Australia, according to a monograph on Veterinary Information Network authored by Mark Rishniw, BVSc, MS, Dipl. ACVIM (SAIM) and Dipl. ACVIM (cardiology). Some cardiologists have used it without marked benefit in cats suffering from dilated cardiomyopathy, and it is contraindicated for hypertropic cardiomyopathy.
Further, pimobendan is intended for use after congestive heart failure occurs, rather than prematurely in cases of degenerative mitral valve disease. Studies are ongoing to determine its value in cats and in the occult or pre-clinical stages of heart failure.
Then there is this: Pimobendan appears to make dogs feel better.
“While the company claims that there is no known psychotropic effect, many clinicians and owners report improvement in quality of life of dogs with congestive heart failure after starting pimobendan, even where heart failure has been well controlled,” Rishniw wrote. “The reason for this improvement in demeanor is unknown.”
Evidence also exists that the drug suppresses pro-inflammatory cytokines, which are implicated in heart disease, the monograph stated.
Idexx’s Cardiocare test measures the cardiac biomarker NTproBNP, the precursor of brain natriuretic peptide. NTproBNP belongs to a family of hormones that are released in response to increased stretch or strain of heart muscle and are natriuretic, a term meaning they promote salt and water excretion. NTproBNP is released early in the heart disease process in both dogs and cats, and rises in proportion to the severity of disease, according to Andrew W. Beardow, BVMS, MRCVS, Dipl. ACVIM (cardiology).
Writing for DX Consult, an Idexx publication, Beardow stated that NTproBNP differentiated cardiac versus respiratory disease, assessed patients with signs of heart disease and with signs of heart failure in both dogs and cats. The test also detected occult heart disease in cats, the article stated.
Antech’s Cardio-BNP test, which came out in May 2011, is a canine-specific assay that measures the blood concentration of B-type natriuretic peptide, a hormone released from the heart in increased amounts due to volume or pressure overload , according to a company press release.
Meanwhile, the basics of congestive heart failure treatment aim to minimize fluid retention, increase blood flow and improve the heart’s pumping efficiency.
Furosemide has long been the diuretic of choice to control fluid buildup. A sodium-restricted diet has been recommended, and several dog and cat food companies make clinical diets designed for heart patients. Making such food palatable could be a challenge, however, and late-stage heart-failure patients are notorious for muscle-wasting and poor appetites.
Finally, ACE inhibitors are used in congestive heart failure treatment in dogs, cats and humans. Enalapril maleate is a vasodilating drug that decreases total peripheral blood flow resistance, pulmonary vascular resistance, and mean arterial and right atrial pressures. It also increases renal blood flow, according to Plumb’s Veterinary Drug Handbook.
MacDonald noted that dilated cardiomyopathy patients, referred to as being in “myocardial failure,” could benefit from digoxin therapy. This drug increases the contractility of heart muscle, thus increasing cardiac output. It decreases sympathetic nerve tone, which promotes fluid diuresis and edema reduction. Digoxin also reduces pulmonary and venous pressure.
In stubborn cases of congestive heart failure, where the maximum furosemide dose is doing an inadequate job, a second diuretic such as thiazide is sometimes added, MacDonald said.
While aldosterone receptor agonists such as spironolactone and eplerenone were reported to improve survival in human heart patients, veterinary studies are so far inconclusive, MacDonald said.