Large-Scale International Study of Feline HCM Provides Survival & Morbidty Data
Heart disease affects 10 to 15 percent of cats, and the most common feline cardiac disorder is hypertrophic cardiomyopathy (HCM). A heartbreaking disease, HCM can cause congestive heart failure, blood clots or sudden death in young, middle-aged and older cats with no prior signs of being ill.
Two things are certain: The disease does not affect every cat the same, and there is no cure for HCM. First identified in people in the 1950s, HCM was recognized in cats in the mid-1970s. Similarities between feline and human HCM led veterinarians to believe that the disease in cats would mimic the sudden death so common in humans.
“Our findings showed that HCM does not cause sudden death in cats anywhere as frequently as it does in people,” says Philip Fox, DVM, MS, DACVIM/DECVIM (Cardiology), DACVECC, head of cardiology and director of the Caspary Research Institute and Education Outreach at the Animal Medical Center in New York City.
“Affected cats do not usually display signs that can suggest they have heart disease, and diagnosis is often suspected after a heart murmur, gallop heart sound or irregular heart rate is detected during a routine veterinary visit,” he says. “Some affected cats develop acute signs such as lung congestion (congestive heart failure) or blood clots, which show up without much warning.”
The lead investigator of a nine-year international epidemiological study to learn more about HCM in cats, Dr. Fox wanted to better understand the risk of congestive heart failure, blood clots and cardiac disease caused by this disease in cats that appeared healthy when first examined. He also wanted to learn how this disease affects survival over time.
“The goal was to determine the incidence rates of cardiac morbidity, that is development of new morbidity (congestive heart failure or blood clots) in cats that were never clinically affected with these complications up to study entry, and also to compare survival between cats diagnosed with both the obstructive and nonobstructive forms of hypertrophic cardiomyopathy, and compare this to healthy cats without echocardiographic evidence of this disease,” he says. “We set out to learn what might happen over time after a healthy cat is diagnosed with hypertrophic cardiomyopathy. This information has not been available.”
The largest feline heart disease study to date began in 2009 and ran four years longer than planned. Funded by Morris Animal Foundation and the Winn Feline Foundation, a nonprofit organization that funds and supports feline health research, the study included 1,730 cats from 50 veterinary centers in 21 countries.
The findings were published in the May-June 2018 issue of the Journal of Veterinary Internal Medicine. The article, titled “International Collaborative Study to Assess Cardiovascular Risk and Evaluate Long-Term Health in Cats with Preclinical Hypertrophic Cardiomyopathy and Apparently Healthy Cats: The REVEAL Study,” provided an insightful glimpse of many aspects of this feline heart disease.
How Veterinarians Diagnose HCM
Hypertrophic cardiomyopathy (HCM) is not easily recognized in affected cats, partly because some cats show no clinical signs before developing a blood clot or breathing difficulty due to heart failure. Sudden death is an uncommon but devastating consequence of this disease in some cats.
A heart murmur or gallop heart sounds may occur in many but not all cats with HCM. Biomarkers such as NT-proBNP or troponins are sometimes used for screening cats suspected of having this disease. The gold standard to diagnose HCM is an echocardiogram. Less expensive than years ago, this diagnostic imaging technique is safe and noninvasive.
“An echocardiographic examination is the most accurate test available for screening cats for this disease or to diagnose disease in cats with clinical signs,” says Philip Fox, DVM, MS, DACVIM/DECVIM (Cardiology), DACVECC, of the Animal Medical Center in New York City.
If rapid or difficult breathing develops, a chest radiograph, or X-ray of the heart and lungs, is used to document the presence of heart failure or help rule out cardiac disease as a cause of breathing distress, particularly when combined with echocardiographic examination.
“If an echocardiogram isn’t practical due to cost or availability, testing for blood concentration of BNP, or the BNP snap test, should be considered,” Dr. Fox says. “If the BNP test is positive, follow-up testing with an echocardiogram is certainly warranted.”
Vicki L. Thayer, DVM, DABVP (Feline), executive director of Winn Feline Foundation, says, “Beyond serving as a screening tool, the BNP test may be helpful in determining quickly in a critical situation if a cat has underlying heart disease. This is being looked at as a possibility by researchers, so I definitely think it’s a helpful tool.”
Understanding the Clinical Signs of HCM
The cause of HCM is suspected to have a genetic basis, but that is not known definitively in most cases. Gene mutations associated with HCM in Maine Coons, discovered in 2004, and Ragdolls, identified in 2007, may play an important role in the disease in these breeds. However, even with the genetic tests, the complexity of HCM can be confusing, as cats that test negative might still develop the disease. In addition to Maine Coons and Ragdolls, other high-risk breeds for developing HCM include British Shorthairs, Sphynx and Persians. Many other cat breeds as well as domestic shorthaired cats are susceptible.
The principal abnormality in affected cats is associated with abnormal thickening (hypertrophy) of the left ventricular chamber. In many affected cats that develop clinical signs, congestive heart failure from fluid accumulation in the lungs (pulmonary edema) occurs rapidly and causes sudden breathing difficulty. Another devastating complication is blood clot formation in the left atrium or left ventricle, which can dislodge or break off and travel suddenly to block blood flow in systemic arteries.
Most commonly, a blood clot travels down the aorta to obstruct the blood supply to the rear legs.
Affected cats usually develop sudden weakness, paralysis and pain, a condition known as arterial thromboembolism (ATE), or “saddle thrombus.” Less commonly, clots can obstruct arteries in the front legs or other organs. Relatively few cats survive ATE.
Among the findings reported by the REVEAL study:
• 30.5 percent of cats with HCM experienced congestive heart failure, ATE or both
• 27.9 percent had cardiovascular death, suggesting that most cats with clinical sigs of HCM die with this disease
• the risk of cardiac death for healthy cats that were not known to have HCM when they were enrolled in the study was about one in 100
“This study was enlightening. It contributed meaningfully to our understanding about the natural history of hypertrophic cardiomyopathy in several ways,” says Dr. Fox. “It identified incidence of
heart failure and ATE across age and over time; it identified risk of cardiac death assessed at one, five and 10 years after cats were enrolled in the study; and it identified long-term survival characteristics. Overall, the risk of cardiovascular death for cats with hypertrophic cardiomyopathy was about one in 15, one in 4.4 and one in 3.5 when assessed at one, five and 10 years following initial diagnosis.”
One finding may change how veterinarians think about this feline heart disease. “Some cats have dynamic obstruction to the left ventricular outflow, called hypertrophic obstructive cardiomyopathy (HOCM),” he says. “People with this condition have a much worse prognosis than those without the obstruction. Because there was no data that demonstrated how HOCM
might affect cats, it was assumed that affected cats were at higher risk, just like affected people with HOCM. But the REVEAL study failed to demonstrate any difference in survival and morbidity between cats with the obstructive and nonobstructive forms of this disease.”
More to Learn
Although much remains to be learned about feline hypertrophic cardiomyopathy, this study provides valuable information. “Hopefully, some of the data from this study provides information that will help veterinarians advise cat owners,” Dr. Fox says. “In addition, these findings are informative and might serve to help develop better health-monitoring strategies or serve as the basis for future clinical trials aimed to discover effective therapies.”
To date, no therapies have been proven to reduce the risk for developing cardiac death in asymptomatic cats with hypertrophic cardiomyopathy. In cats that develop congestive
heart failure, diuretics are administered to resolve pulmonary edema, and other medications are given on an individual basis. Medications to prevent blood clots in at-risk patients include antiplatelet-aggregating drugs. While significant irregular heart rhythms are uncommon, several drugs including a beta blocker may be prescribed in selected cases, usually to slow a rapidly beating heart.
Routine physical examinations continue to contribute importantly to heart health. “If a veterinarian hears a heart murmur, it is usually suggested that additional tests are conducted in order to assess whether significant underlying heart disease is present, or whether the heart murmur is of no consequence,” says Vicki L. Thayer, DVM, DABVP (Feline), executive director of Winn Feline Foundation. “It may turn out that heart disease is not present, but it is worth further evaluation to learn more.”
“A lot still needs to be done to identify effective drugs with proof that they reduce morbidity and risk and improve the outcome for cats with HCM,” says Dr. Fox.
Dr. Thayer agrees. “We would like to see more ways to diagnose HCM earlier and better that might aid preventive care. So much more is needed in the area of treatment. HCM is a tough disease, one in which it will take many small steps before there is a giant leap.”
The Ricky Fund: A Lifesaver for HCM
The heartfelt loss of a beloved Devon Rex named “Ricky” set in motion the beginning of a fundraising campaign to support research of the disease that tragically cut short the cat’s life at 4 years old. Since owner Steve Dale founded the Ricky Fund in 2002 along with the Winn Feline Foundation, more than $200,000 has been raised for studies of hypertrophic cardiomyopathy (HCM).
Dale, a nationally syndicated pet columnist and Chicago radio show host, established the fund to learn more about the heart disease. Since 2003, the Ricky Fund has supported 14 HCM research studies totaling over $183,000. Two were studies that led to the discoveries of the gene mutations for HCM in Maine Coons and Ragdolls.
Highly socialized and quick-witted, Ricky was featured on local and national TV shows playing improvisational piano and performing tricks like jumping through a hoop. Dale and his wife, Robin, often would walk Ricky on a leash with their dogs. They were quite fond of their Ricky when the veterinarian detected a heart murmur that was later confirmed by echocardiogram to be HCM.
A member of the Winn Feline Foundation board of directors, Dale says, “When it comes to feline health studies, Winn had been a primary funder for decades. I am so pleased that the Ricky Fund has done so well. Ricky’s life and death is making a difference to cats with HCM and their families who love them.” For information about the Ricky Fund, click here.
Purina appreciates the support of the Winn Feline Foundation, particularly Vicki L. Thayer, DVM,
DABVP (Feline), executive director, in helping to identify this topic for the Purina Pro Plan Cat Update.