August 12, 2015
Originally published in the August 2015 issue of Veterinary Practice News. Subscribe today!
A loud murmur may not indicate heart disease in a dog, and conversely, a dog with heart disease may not necessarily have a loud heart murmur.
That was the top piece of advice to general practitioners offered up by Pamela M. Lee, DVM, Dipl. ACVIM (Cardiology), an assistant professor in veterinary clinical sciences at Washington State University College of Veterinary Medicine.
In older, small- to medium-size breed dogs, the most common heart diseases are degenerative issues, such as endocardiosis, also called chronic degenerative-valve disease or acquired valvular heart disease, Dr. Lee said.
For large-breed dogs, the most common heart disease is dilated cardiomyopathy, where heart muscle contracts poorly, Lee said.
When checking for endocardiosis, it’s the type of heart murmur, not the loudness, that a practitioner should listen for.
“One of the big things to know, at least with endocardiosis: The severity of the heart disease does not correlate with a loud heart murmur,” Lee said.
This may be important to keep in mind, because experts spoken with, including Lee, pointed to degenerative-valve disease as the most common heart disease in older dogs.
Chloe Thorn, DVM, with the Ryan Hospital at University of Pennsylvania School of Veterinary Medicine, sees a lot of degenerative-valve disease in older dogs.
“The mitral and tricuspid valves separate the atria from the ventricles,” Dr. Thorn explained. “In a normal dog, the valve leaflets are thin and close with a tight seal, preventing any blood from going backward in the heart with each heartbeat. As some dogs age, the valve leaflets become thickened and cannot seal properly, which causes blood to leak backward in the heart and results in a heart murmur, which a veterinarian can detect by listening to the chest with a stethoscope.”
This valve disease may be mild, and cause no symptoms in a dog’s lifetime, but in other dogs, the leaks in the valves can be severe and can cause the heart to enlarge. This can ultimately result in fluid build-up in the lungs, she said.
“This fluid is by definition congestive heart failure, and results in symptoms at home, including cough and trouble breathing,” Thorn said.
Sandra Tou, DVM, Dipl. ACVIM (Cardiology and Internal Medicine), clinical assistant professor of cardiology at North Carolina State University College of Veterinary Medicine, also said that the culprit behind the majority of older dogs she sees with heart problems is chronic valvular heart disease.
However, many dogs show no symptoms, Dr. Tou said.
“Thankfully, many affected dogs will remain asymptomatic in their lifetime, but severely affected dogs can develop complications, including congestive heart failure,” Tou said. “The earliest sign of the disease is often the detection of a left-sided systolic heart murmur, which stresses the importance of a complete annual health exam. Detection of such a murmur warrants further diagnostic testing to best assess the stage of disease.”
If a worst-case scenario like congestive heart failure develops, Thorn said the fluid in the lungs can be cleared with diuretic medications.
“Once an animal develops heart failure, they must be on lifelong medications,” Thorn said.
Most dogs with congestive heart failure can be managed with medications and have great quality of life and be symptom-free for several months.
“Over time, heart failure can become difficult to control due to development of resistance to treatment or side effects of the medications,” Thorn said.
To treat severe heart disease, Lee uses Pimobendan, Enalapril or ACE inhibitors.
“The need for medication depends on the severity of the heart disease,” Lee said.
Different mediations have varying reports of success, and Lee noted that she’s waiting on an ongoing study on Pimobendan.
The drug has already showed promise in prolonging an affected dog’s life.
An early study from 2012 on the medication, “Efficacy of Pimobendan in the prevention of congestive heart failure or sudden death in Doberman Pinschers with preclinical dilated cardiomyopathy,” was conducted on 76 dogs in the U.S. and U.K.
The results, published by the American College of Veterinary Internal Medicine, was nearly 200 more days of life.
“The administration of Pimobendan to Dobermans with preclinical DCM prolongs the time to the onset of clinical signs and extends survival,” the study’s conclusion states. “Treatment of dogs in the preclinical phase of this common cardiovascular disorder with Pimobendan can lead to improved outcome.”
No drugs can cure heart disease in dogs, but Lee said the drugs she prescribes can help with the goal of slowing down its progression.
“At this time, it’s not 100 percent successful,” Lee added.
While some experts said asymptomatic dogs do not need to be treated, Tou with NCSU said that even dogs with enlarged hearts, but no symptoms, may benefit from medical therapy.
“Dogs with congestive heart failure warrant additional medical therapy to prevent pulmonary edema and optimize cardiac function,” Tou said.
Lee was optimistic about ongoing research to better treat dogs with heart disease. Beside studies on Pimobendan, there are also experts examining the benefit of surgical valve replacement, she noted.
Of course, preventing congestive heart failure is priority number one, Lee said.
“A big concern with the heart disease is that [it can] become severe enough to cause complications,” she said.
However, endocardiosis, though a big concern, doesn’t always result in death.
Sometimes, this disease progresses slowly, and a dog may die from something else. The primary indicator of whether a dog will develop congestion heart failure depends on how fast the disease progresses, Lee said.
“One thing I think veterinarians should be aware of is not all dogs with endocardiosis develop congestive heart failure,” Lee added.
The most common heart disease in cats is hypertrophic cardiomyopathy, Thorn said.
“This is a disease of the heart muscle which causes it to become thickened and stiff,” Dr. Thorn said. “This limits the ability of the heart to fill properly, and can also, ultimately, result in congestive heart failure.”
Tou noted that hypertrophic cardiomyopathy results in hypertrophy of the myocardium.
“Middle-age cats are most commonly affected by HCM, although the disease does affect a wide age range,” Dr. Tou said.
Tou’s advice to veterinarians who encounter cats with heart murmurs or gallop sounds is to have them evaluated for underlying cardiac and metabolic disease.
However, changes in a cat’s heart can be due to other factors, Lee said.
Diseases like high blood pressure (systemic hypertension), or hyperthyroidism, can cause heart changes as well.
Detecting heart disease in cats isn’t as easily as finding it in their canine cousins.
“Cats hide heat disease much more easily,” Dr. Lee said.
Cats can have normal auscultation of heart and still have heart disease, but in some cats, a loud murmur may not indicate heart disease, Lee said.
There are a variety of medications to treat the disease, Pimobendan being one of the preferred.
A 2014 study, “Case-control study of the effects of Pimobendan on survival time in cats with hypertrophic cardiomyopathy and congestive heart failure,” looked at seven cats receiving treatment with Pimobendan and 27 cats receiving treatment without Pimobendan.
“Cats receiving Pimobendan had a significant benefit in survival time,” the study concluded. “Median survival time of case cats receiving Pimobendan was 626 days, whereas median survival time for control cats not receiving Pimobendan was 103 days.”
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