[From Tufts Febuary 2010 Issue]
CONGESTIVE HEART FAILURE IN DOGS: OVERVIEW
1. Keep your dog fit and trim. Excess weight can stress the heart and lungs.
2. Walk him on leash but avoid vigorous activity.
3. If your dog takes a diuretic, provide access to water at all times.
4. Feed a well-balanced diet with a moderate amount of sodium. Specially formulated commercial diets are available for dogs with heart conditions.
5. Keep a diary of his behavior, appetite and medications.
6. Monitoring his breathing rate and effort may allow detection of worsening heart failure before it warrants hospitalization. The normal breathing rate: fewer than 35 breaths per minute with no abdominal effort. Contact your veterinarian if you detect a faster rate.
Despite its ominous sounding name, congestive heart failure (CHF) doesn’t necessarily mean a dog can’t live out his life fetching, foraging and frolicking. With advances in medicine, dogs with heart failure enjoy longer, healthier lives than once thought possible.
“A diagnosis of heart failure is not a death sentence,” says cardiologist Suzanne Cunningham, DVM, at Cummings School of Veterinary Medicine at Tufts University. “Dogs can do well for many months or more with close monitoring and the care of a dedicated owner.”
In the future, dogs also may find relief in several promising catheter-based procedures under investigation at Cummings School and other institutions. If successful, the new treatments will provide minimally invasive techniques for repairing bad valves and slowing the progression of chronic valvular disease, the leading cause of heart failure in dogs.
Tracking The Dog’s Blood Flow
Heart failure is the inability of the heart to pump effectively. The heart consists of a right and left side, with each subdivided into an upper and lower chamber, called the atrium and the ventricle. The right ventricle receives blood from the body, then propels it to the lungs, where carbon dioxide is exchanged for oxygen. The left atrium then accepts the oxygen-rich blood and passes it to left ventricle, which forces it back into the body.
The heart contains four one-way valves to keep the blood flowing forward as it pumps: two are situated between the atria and ventricles, and two are located where the blood exits the ventricles on its way to the lungs or body. When there’s a breakdown in this pumping machinery — for example, a chamber weakens or valve deteriorates — the heart is no longer able to propel blood at the needed volume, pressure and direction. This causes blood to logjam in the vessels around the heart, and the congestion disrupts the delicate balance of pressure between the inside of the vessel walls and the tissues they feed.
Eventually, fluids from the blood leak through the vessels and into the surrounding tissues, most notably, the lungs and abdomen. This sparks any number of symptoms: fainting, coughing, shortness of breath, labored breathing, loss of appetite, lethargy, rapid or irregular heart beats, abdominal distension and discomfort when lying down. Unfortunately, no prevention or cure exists.
Common Causes of Heart Failure in Dogs
The two most common causes of heart failure are chronic valvular disease, which typically affects older, small breeds, and dilated cardiomyopathy, usually found in large and giant breeds beginning in middle age. While the root cause of these conditions remains a mystery, heredity plays a key role.
Approximately 10 percent of all dogs seen by primary care veterinarians in the U.S. have some form of heart disease. And 75 percent of the dogs — slightly more males than females — have chronic valvular disease. It occurs when one of the heart’s valves slowly deteriorates and can no longer sufficiently stop the backflow of blood. This frequently involves the mitral valve, located between the left atrium and left ventricle. Breeds most at risk are Cavalier King Charles spaniels, miniature and toy poodles, Chihuahuas, Yorkshire terriers, schnauzers and cocker spaniels.
The first sign is often a heart murmur. It becomes louder over time as the valve progressively deteriorates and the volume of blood flowing backward increases. A veterinarian can often detect this with a stethoscope years before the dog displays outward symptoms.
Because of conflicting information and unanswered questions about what therapies work best at what stage, the American College of Veterinary Internal Medicine charged a panel of 10 cardiologists to develop a consensus statement. The report, “Guidelines for the Diagnosis and Treatment of Canine Chronic Valvular Heart Disease,” appeared in the November/December 2009 issue of the Journal of Veterinary Internal Medicine. The panelists divided the disease into four progressive stages and detailed specific treatments they agreed and disagreed on for each stage. If your dog is diagnosed with this disease, ask your veterinarian to consult the report.
Of their many recommendations, contributor Sonya Gordon, DVM, at Texas A&M University College of Veterinary Medicine and Biomedical Sciences, says: “Dogs with murmurs should have their disease staged, by [X-rays] … to determine how big their heart is so we can have a very active surveillance program, and heart disease doesn’t go unnoticed in its very early stages and patients don’t have to seek an emergency room.”
Dilated Cardiomyopathy in Dogs
The second most common cause of heart failure is dilated cardiomyopathy, a progressive weakening of the heart’s muscle. Typically, both the left and right ventricles are affected, but the left-sided disease is often more pronounced. In dogs with this condition, a heart chamber’s walls thin as the chamber grows in size. Like a rubber band that’s been stretched too much, the chamber slowly loses its elasticity until it’s unable to snap back forcefully enough during contraction. This causes fluids to back up, which ignite the telltale symptoms of heart failure, generally beginning between 4 and 10 years of age. Male dogs weighing 50 pounds or more are predisposed to the condition, with the highest rate of incidence in Doberman pinschers, followed by boxers. Great Danes, Irish wolfhounds and Newfoundlands are also at risk.
“Dilated cardiomyopathy is thought to be a genetic disease that has some environmental factors that affect the age of onset and the rate of progression,” Dr. Cunningham says. “We don’t really know all of the genetic components of the disease yet. We also don’t know, oftentimes, what causes one dog to develop it at 2 years of age and another dog to develop it at 10.”
Regardless of the unsolved triggers that set dilated cardiomyopathy and valvular disease in motion, the reason dogs don’t display easily recognizable symptoms for months or years is that their bodies compensate in other ways: Blood vessels constrict, the heart rate quickens and the body signals the kidneys to hold onto salt and water to expand the blood’s volume. These physiological tweaks coalesce to maintain the blood pressure needed to keep the vessels coursing with blood and supplying blood to the organs.
However, increased blood volume eventually leads to greater fluid buildup and increased workload on the heart, ultimately making it harder for the heart to move blood forward. These short-term fixes lead to an overall worsening of the dog’s condition.
Diagnostic Testing for CHF in Dogs
To diagnose CHF, veterinarians use a stethoscope to listen to the dog’s heart and lungs for irregularities, and check his blood pressure, which can be too low or too high. Possible tests include a chest X-ray to look at the lungs for fluid accumulation; an electrocardiogram, or EKG, which measures the electrical activity of the heart; blood work to monitor the progression of the disease and the effects of medications on organs; and an echocardiogram — an ultrasound test that uses sound wave technology to generate pictures of the heart’s structure and performance.
A new blood test allows detection of a protein — called NTproBNP — that is released into the bloodstream in significant heart disease and released in greater quantities in the presence of heart failure. This test may allow detection of early asymptomatic dilated cardiomyopathy and aid in the diagnosis of heart failure.
While a dog might not need these or other tests at the same time, expenses can add up. At Cummings School, an echocardiogram costs about $250 and X-rays about $180. Dogs already in heart failure who go to the emergency room there can expect a bill of about $2,000.
Treating Congestive Heart Failure in Dogs
Because no cure exists for most cases of heart failure, veterinarians focus on alleviating symptoms and delaying its progression by ridding the body of excess fluids. This usually requires a combination of medications. Some of the most common include furosemide, a diuretic which blocks the kidneys’ ability to hold onto salt and water, causing the dog to urinate more frequently; ACE inhibitors such as enalapril, which decrease the constriction of blood vessels and helps furosemide work more effectively; and pimobendan, which improves the heart’s effectiveness by strengthening the force of contractions, and dilating blood vessels.
Approved for use in dogs by the Food and Drug Administration in 2007, pimobendan has been deemed a “wonder drug” by many dog owners, including Barb Hoorman of Plano, Texas, a breeder of Cavalier King Charles spaniels. In 2002, two of her companion spaniels — Stormy and Midori, each about 10 years old at the time — went into heart failure within two weeks of each other.
She took them to Texas A&M, where she screens her dogs each year as part of the breeding protocol. Dr. Gordon was conducting one of the first pimobendan clinical trials in the U.S. and asked her if she wanted to participate. Within 36 hours, her dogs were acting like puppies again, Hoorman says. “It was just extraordinary. It was a life-saving drug.”
Furosemide and enalapril are now available as generics and qualify for the $4-prescription programs offered by large retail pharmacies such as Walmart and Target. Pimobendan, however, is more expensive because it’s offered only under its brand name, Vetmedin. Dr. Gordon estimates owners can expect to pay about $12 a month for furosemide and enalapril combined, and about $60 a month for pimobendan — more if the dog is large. Veterinary visits will run an additional $200 to $300 every three or four months.
Veterinarians might also recommend the use of beta blockers. Although they improve the prognosis of heart failure in people, their effectiveness in dogs is unproven. Veterinarians might also prescribe natural supplements such as amino acids or omega-3 fatty acids, which have been shown to have beneficial effects in dogs.
At present, dogs with heart failure have limited surgical options. Cummings School and other universities that previously offered heart bypass surgery aren’t performing them. Costs can range between $10,000 and $15,000 for the procedure and hospitalization alone. The mortality rate may range between 20 to 30 percent, and many dogs are simply too small for the surgery.
Through a combination of medications, a balanced diet with moderate sodium and regular visits to her veterinarian, Hoorman says that Stormy lived until he was 12 and Midori until she was 13 — considerably longer than the six-to-nine month average survival time quoted for dogs with heart failure.
“The hard part in talking about survival in dogs is that a lot of it is owner-dependent,” Dr. Cunningham says. “There are some dogs that have gone 12, 15, 18 months after diagnosis. These are dogs with very motivated owners.”