Originally published in the October 2015 issue of Veterinary Practice News. Enjoyed this article? Then subscribe today!
One type of heart disease appears to be responsible for the lion’s share of cases seen in cats.
“The vast majority of the cardiac disease we see in cats is due to some form of cardiomyopathy — primary heart muscle disease,” said Mark D. Kittleson, DVM, Ph.D., Dipl. ACVIM (cardiology), a professor emeritus at the UC Davis School of Veterinary Medicine.
“Hypertrophic cardiomyopathy probably accounts for 60-70 percent of that.”
Dr. Kittleson, who also works for the Veterinary Information Network, said HCM can be passed down from some cats to their offspring.
“It’s known to be heritable in Maine coons and ragdolls, where causal mutations have been identified,” Kittleson said. “Many other breeds get HCM, but most of the HCM seen is in crossbred cats.”
HCM is not present at birth. It develops over time and can show up as early as 6 months of age. However, it is often identified for the first time in a geriatric cat.
Kittleson explained that the disease causes a thick left ventricle, which then “has ongoing cell death in it — probably because of inadequate blood supply,” he said.
This condition results in fibrosis, which leads to a left ventricular chamber that is stiffer than it should be, Kittleson said.
“This leads to a higher than normal pressure in the LV during diastole and that creates higher than normal left atrial and pulmonary capillary pressures,” Kittleson added.
In turn, that increased pressure causes left atrial enlargement and left heart failure (pulmonary edema and/or pleural effusion).
He describes the process as blood flow slowing down in the large left atrium, which predisposes the patient to clotting.
“Once a large thrombus forms, it has a tendency to break loose and embolize the aorta — feline aortic thromboembolism or FATE,” Kittleson said.
Kittleson says there are several forms of cardiomyopathy: restrictive, unclassified and dilated cardiomyopathy.
“Taurine deficiency used to be a major cause of DCM, but is identified only rarely currently,” he said.
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare form of feline cardiomyopathy. Rarely cats will also get other types of cardiac disease, such as myxomatous mitral valve degeneration and myocardial infarction, he added.
“Other than administering taurine to a cat with DCM due to taurine deficiency, there are no known cures for cardiomyopathy and we don’t know of anything that slows the progression of any other form of cardiomyopathy,” Kittleson said. “Consequently, the primary aims of therapy are to prolong the quantity and quality of life in cats that are in heart failure due to a cardiomyopathy and to prevent a left atrial thrombus from forming.”
John Rush, DVM, MS, Dipl. ACVECC, Dipl. ACVIM, a professor at Cummings Veterinary Medical Center at Tufts University, said current treatments for congestive heart failure in cats vary based on personal preferences.
Most veterinary cardiologists use furosemide (a diuretic), and ACE inhibitors like enalapril, benazepril, or lisinopril, once congestive heart failure is present, Dr. Rush said.
Congestive heart failure is identified in cats by the presence of dyspnea or respiratory compromise, plus evidence of pulmonary infiltrates on thoracic radiographs, which Rush said would ideally be supported with an elevated NT-proBNP concentration and/or echocardiography since confirming CHF in cats can be difficult.
“In cats with some forms of cardiomyopathy, many veterinary cardiologists will prescribe pimobendan for management of CHF, but most would be uncomfortable giving pimobendan to cats with documented left ventricular outflow tract obstruction, a condition that commonly accompanies hypertrophic cardiomyopathy,” Dr. Rush said.
“Thus, for most veterinarians in general practice, unless an echocardiogram has been done and left ventricular outflow tract obstruction has been excluded, it might be safest–at this time–to not administer pimobendan.”
Kittleson called prevention of left atrial thrombus formation is “a relatively easy topic.”
“Only clopidogrel (Plavix) has been shown to be efficacious,” Kittleson said. “In my humble opinion, aspirin, which is commonly prescribed for this purpose, is ineffective. Plavix and aspirin can be combined but it is not known if the combination is more effective than Plavix alone.”