Ricky Fund Supported Study on a Drug Used for Cats with HCM
Here’s a trivia question: What’s the number one cause of death in (indoor only) cats from around 2 years of age to 8 or 10 years of age? No one really knows for certain, as there is no CDC for pets, but likely it’s a kind of heart disease called feline hypertrophic cardiomyopathy (HCM). For sure, we do know that HCM is the number one cause of sudden death in cats. And we know HCM is common, and there is no known treatment.
I had a cat who changed my life. His name was Ricky. He succumbed to HCM in 2002. Back in the day, Ricky was a sort of TV star, appearing on shows, including National Geographic Explorer, CNBC, a Canadian TV show called The Pet Project, and many other national programs, including about every local TV station in Chicago as well as appearances on WGN Radio.
That’s because Ricky played the piano. Yes, you read that right—a children’s piano. You can even watch one of those TV appearances, from PBS Pet Part of the Family. Ricky loved to appear in public. He could also jump through hoops; jump over dogs on a down stay, offer a “high four;” sit when asked to; and come when called.
Today, YouTube videos are filled with cats doing tricks, and Samantha Martin is touring the country with Acrocats. But back then, a cat going out into the world and doing “tricks” was considered an oddity to say the least.
Perhaps as a result of us working together, Ricky and I had an extraordinary bond. He slept with my arm around him every night, greeted me at the door, and frequently spoke to me. He also seemed to read my mind.
During one routine veterinary visit, the veterinarian heard a murmur, and the visit turned out not to be routine after all. A veterinary cardiologist confirmed on an echocardiogram that Ricky had an enlarged thickened heart muscle, a condition known as HCM.
Cats with HCM often do live out normal lifespans, even asymptomatic, and ultimately die of kidney disease or cancer.
However, some cats with HCM may develop an aortic thromboembolism, or “saddle thrombus.” This is a serious condition in cats in which a thrombus (blood clot) affects the blood flow to the hind legs of the cat. It’s painful for the cat, but can be treated as an emergency. Cats do regain movement of their legs again. The problem is that typically once this occurs, it will occur repeatedly. Not only does this cause the cat great pain, but repeated emergency visits get costly. Sometimes the events worsen with each occurrence. After several of these occurrences, the victim is usually euthanized.
Some cats with HCM go into heart failure, a condition that requires supportive care and medications. Cats can live with heart failure for a time, but ultimately their quality of life diminishes and they are also euthanized.
Other cats with HCM can suddenly die. No decision to make regarding euthanization, but that is heartbreaking to see happen. And that is what happened to Ricky. For several weeks, his health seemed to be waning, but then one day he just dropped. And that was it.
I know from reading the email and, at that time ‘snail mail,’ that Ricky had touched thousands, changing their image of what cats’ potential could be. But to me, he was simply my best buddy. No dog will likely ever fill the place in my heart that Ricky occupied.
I thought, This has to stop; we need to do something about HCM. So, I launched the Ricky Fund with the nonprofit funder of cat health studies, the Winn Feline Foundation. We’ve raised more than $100,00, but there’s no cure or treatment in sight. Some drugs that have seemed promising haven’t panned out, but we needed to do the studies to find out. What follow is a report of a recent study funded by the Ricky Fund.
Hypertrophic cardiomyopathy (HCM) is the most common heart disease of cats. In HCM, the myocardium of the left ventricle hypertrophies concentrically and stiffens, which results in diastolic dysfunction and ultimately increased left atrial pressures and distension of the left atrium. This disease may be subclinical throughout some or all of an affected cat’s life, but when it progresses to clinically evident dysfunction, congestive heart failure (CHF), thromboembolic disease, and even sudden cardiac death may be the result. When subclinical HCM is detected in a cat, both clinicians and owners experience great concern as there are no evidence-based prophylactic therapies that are clinically proven to prevent progression to clinical disease, and once clinical disease does occur, even the short-term prognosis may be poor to grave.
Atenolol, a beta-1 adrenergic receptor antagonist, has often been used empirically in the treatment of cats with subclinical HCM, and is thought by many clinicians to be of benefit to these animals. In this study of client-owned cats with subclinical HCM, cats were included if they had echocardiographic evidence of diffuse or segmental left ventricular hypertrophy, but were excluded if they were found to have systemic hypertension or hyperthyroidism. In addition to echocardiography and Doppler blood pressure measurement, the cats were also evaluated with cardiac auscultation, electrocardiography and 24-hour Holter monitoring. Seventeen cats (14 neutered males and 3 spayed females) completed the study; the median age of the animals was 7.0 years (range, 4 years-17 years). Of the 17 cats, 11 had left ventricular outflow tract obstruction (LVOTO) secondary to systolic anterior motion (SAM) of the mitral valve, and 6 did not have this echocardiographic abnormality.
Results of the above described clinical evaluations were compared in the subjects before and then 2-4 weeks after starting atenolol therapy at 6.25-12.5 mg PO q 12 hours. Echocardiography demonstrated that LVOT velocity, and therefore LVOT obstruction, decreased in the patients after at least 2 weeks of atenolol administration. Cardiac arrhythmias were not found in many of the patients until Holter monitoring was performed. In humans, there is a known association between the occurrence of non-sustained ventricular tachycardia and risk of sudden cardiac death, and also in humans with HCM, 88% had ventricular arrhythmias demonstrated by Holter monitoring, and 31% had ventricular tachycardia. One previous study showed that 100% of cats with subclinical HCM have arrhythmias.
Atenolol was also found to decrease heart rate, heart murmur grade, and to a lesser degree, ventricular ectopy, in cats with subclinical HCM. The frequency and complexity of ventricular arrhythmias in the study cats was reduced with atenolol use; atenolol is also a ventricular and supraventricular antiarrhythmic agent. It is still unknown if administration of this drug results in reduced incidence of sudden cardiac death in cats with HCM, or a longer period of time before subclinical HCM progresses to CHF. As only cats with mild subclinical HCM were included in the study it is unknown if atenolol adminstration also positively affects cardiac function parameters in cats with more severe HCM or actual clinically evident heart disease. Given the promise atenolol has shown in improvement of cardiac function in this small population of cats with subclinical HCM, additional studies in cats with more severe or clinically evident disease are warranted. [PJS]