The latest hubbub in cardiology

No matter what your specialty is in veterinary medicine, chances are good you will come across a patient with a heart murmur and patients with underlying cardiac disease; occult or apparent. While you may not ultimately treat patients with heart disease, staying current on trends classifying heart disease and the medical management of disease and treatment and prevention of congestive heart failure (CHF) remains paramount.

Keys to preventing the onset of severe disease include recognizing a patient’s risk, understanding how to treat, and knowing what tools, including pharmaceuticals, are available and currently recommended.

Cardiac disease management

Veterinary cardiology has come a long way in the past 30 years. With the advent of digital radiography, we have improved our ability to identify cardiac and noncardiac thoracic changes in the chests of various species. With cardiac biomarkers, we have improved our ability to diagnose cardiac vs. non-cardiogenic causes of respiratory disease and related problems. Smartphones and associated apps allow clients to monitor patients at home, and we can have bedside tests that efficiently transmit various parameters in our patients, from heart and respiratory rates to ECGs and more. There is even an app out there now to assist owners in monitoring a pet’s resting respiratory rate.¹

Modern technological advances, however, do not replace a thorough examination, auscultation, and history-taking. Further, if warranted, we need to know how and when to utilize these various tools to establish a treatment plan for each pet. Treatment is based on the underlying cardiac condition, and mainstays include monitoring, re-assessment, medical therapies, and keeping abreast of current recommendations.

A brief review

As vets, we know all too well not all species are created equal. The same can be said about the types of heart disease seen in various species and even among breeds within a species.

Hypertrophic cardiomyopathy (HCM)
A disease of the heart sarcomere, the unit of cardiac contractility, HCM causes abnormal myocardial left ventricular hypertrophy and abnormal diastolic function, with or without obstruction of the left ventricular outflow tract. This condition is most commonly appreciated in feline patients.

A genetic link has been identified in Maine coons. Otherwise, it can afflict any cat at any age, with an estimate of almost 15 percent of all cats being afflicted, with the majority being asymptomatic.^2,3

Dilated cardiomyopathy (DCM)
DCM occurs as a result of myocyte loss either due to decreased function or number loss with an accompanying decrease in the contractility of the heart. This condition most commonly affects dogs; and rarely cats.

Breed predispositions commonly affect large and giant breed dogs, (e.g. Great Danes, boxers, Dobermans, and Irish wolfhounds). Nutritional deficiencies and toxicities can also contribute to the development of DCM.⁴

Myxomotous valvular disease (MMVD)
Accounting for about 75 percent of canine heart disease cases in North America, MMVD affects the valves in the heart. The mitral and left atrioventricular nodes are affected in 70 percent of cases.

Generally, breeds under 20 kg are overrepresented, with males at 1.5 times higher risk than females. Over time, the structure of the valve of concern becomes deformed, leading to valve leakage. Gradually, this leads the heart to work harder, resulting in eccentric hypertrophy of the left ventricle and atrium and eventual cardiac failure.⁵

The American College of Veterinary Internal Medicine (ACVIM) has established guidelines to unify the terminology and classification of heart disease in our patients (See Figure 1 for a schematic of the grading system used.) It is critical to remember medical management for dogs with MMVD stage B2 or higher is medically indicated.^5–7 Medications used to treat MMVD vary depending on the stage of disease, the severity of clinical signs, and other pet and owner-specific factors.

Arrhythmogenic right ventricular cardiomyopathy (ARVC)
ARVC, or “boxer cardiomyopathy,” is most notably associated with boxers. Still, it has been reported in other breeds; rarely in cats. In this condition, the right ventricular heart muscle’s gradual deterioration occurs due to eventual replacement by fibrous adipose tissue. Faulty conduction of the electrical activity within the heart contributes to irregular heartbeats and arrhythmias. Negative impacts on cardiac function contribute to clinical signs commonly seen, including syncope.⁸ Medical management may include a beta-blocker (e.g. sotalol) +/- mexilitine (antiarrhythmic).^9,10

Systemic hypertension/pulmonary hypertension
We recognize systemic hypertension as a primary illness in our feline patients. At the same time, in dogs, it is usually secondary to other underlying diseases (e.g. cardiac or renal conditions). Failing to treat systemic hypertension early on can lead to target organ damage and long-term ill effects.

Our main options for therapy include calcium-channel blockers (e.g. amlodipine, angiotensin-II receptor blockers (ARB) (telmisartan), and angiotensin-converting enzyme inhibitors (ACEI) (enalapril). Species variations and other variables play a role in therapy selection.^11,12

Pulmonary hypertension is a diagnosis made on echocardiography, and given this condition is rare as a primary condition, except in humans, identifying the underlying cause and treating both conditions is paramount.

Therapy usually includes treatment of the underlying cause, and in dogs, sildenafil, a phosphodiesterase type 5 inhibitor, is our mainstay. Pimobendan also has benefits in managing pulmonary hypertension in dogs with left-sided CHF because it aids in lowering arterial pulmonary pressure.¹¹

Medical management strategies

Classically and more recently, we have amassed a decent pharmaceutical armory to address the various types of heart disease seen in our veterinary patients (See: “Managing the heart.”) We utilize multiple classes of medications and often combinations of therapies to medically manage disease, prevent disease progression, and treat CHF and related decompensatory states.

Managing the heart Medication classes commonly used in the management of small animal cardiology include:5,9,13,16,20–31 • ACEIs, e.g. enalapril and benazapril • Pimobendan, an inodilator • Loop diuretics, e.g. furosemide and, more recently, torsemide • Aldosterone antagonist, namely spironolactone • Vasodilators, e.g. hydralazine (arterial dilator), nitroglycerin, and the most potent, nitroprusside • Cardiac glycosides, e.g. digoxin • Thiazide diuretics e.g. hydrochlorothiazide • Beta-blockers, e.g. atenolol (most commonly in cats) and Sotalol (key for ARVC) • Antiarrhythmics, e.g. mexiletine for ARVC • ARBs e.g. telmisartan in the treatment of hypertension (and PLN) • Calcium channel blockers, e.g. amlodipine in the treatment of hypertension • Anticoagulants e.g. clopidogrel and aspirin

As a small animal practitioner, it is best to recognize the various drug classes, understand their mechanism of action, indications for use, and, most importantly, when not to use them. Gone are the days when we treat a heart murmur simply because we auscult it. We want to make evidence-based medical decisions, ideally with as much information at our fingertips as possible.

Using diagnostics, clinical signs, and professional guidelines, such as those provided by the ACVIM for treating and diagnosing MMVD in dogs, is paramount to ensuring safe, effective care that can support human-animal bond (HAB) and preserve longevity and quality of life.

Combo therapy and hypertension therapy
In addition to commonly used drugs, we now have a labeled combination therapy product to aid in managing dogs with CHF and a veterinary-labeled ARB for managing hypertension in cats.

1. Cardalis. This provides one of the first combined fully veterinary-approved cardiac medications. It contains a chewable combination of spironolactone and benazepril hydrochloride. While not for every patient, for our canine patients, where med administration can be challenging, it can decrease the number of meds needed, and improve compliance and treatment success rates.^5,13–15
   
   Per the ACVIM guidelines and Dr. S. Ettinger, the use of Cardalis is recommended in the management of MMVD classes C and D.⁵
2. Semintra (Telmisartan). While not new to the U.S. market, it is still not used by all practitioners. Whether it has a place on your shelf is purely up to you. However, recognizing that a veterinary-approved product is labeled for managing feline hypertension is valuable knowledge. It comes as a liquid that can aid in administration. While not yet labeled for use in dogs, this can be used off-label for those with challenging systemic hypertension management.^16,17

   

What’s new in the medication pipeline?

Cardiology medical management frequently gets updates and modifications on drug doses, combinations, and recommendations to prevent CHF. Heart disease can be costly to treat over time, and if CHF hits, costs can skyrocket. We now have some generic alternatives that are FDA-labeled for use in dogs to treat cardiac disease.

• Vetmedin (pimobendan), a key drug in managing cardiac disease in cats and dogs, still seems novel despite becoming available in the U.S. in 2007. This drug helped revolutionize the management of CHF and continues to help prevent CHF onset in our canine and feline patients, both on and off-label. However, it is not always financially feasible for some owners. Having a generic available may help bring treatment to greater numbers and earlier in the disease process, helping to ward off CHF longer, maintaining quality of life, and the HAB between pet and pet parent.
• Generic pimobendan. With Vetmedin’s patent up, a generic formulation of pimobendan, the active ingredient in Vetmedin, is now feasible. According to an April 2024 CVM update, the FDA recently approved a generic chewable indicated for dogs to aid in the medical treatment of any stage of MMVD or DCM, including severe CHF in dogs.¹⁸ The product uses the same concentration, dose, and active ingredient as the original inodilator, Vetmedin. All inactive ingredients prove safe and do not alter the drug’s bioavailability, making it a safe and effective alternative to the trade-name product. For some owners, this could be life-changing when cost concerns limit treatment options and drug choices.^18,19
• Generic torsemide. Another potentially key generic cardiac medication for dogs recently received conditional approval (May 2024). Known as UpCard-CA1, it is an oral solution containing torsemide, a loop diuretic with double the NA:K excretion rate than furosemide.^18,20 It is labeled for treating dogs in CHF with pulmonary edema secondary to MMVD. Recommendations based on labeling are to use this in combination with spironolactone, an ACEI, and pimobendan.

Approval is conditional for one year with the possibility of up to four yearly renewal cycles. During the conditional time, the manufacturer must continue to provide data and evidence that completes the necessary effectiveness data required for full drug approval. ¹⁹

What’s ahead?

Though not widely available (or cost-effective for most), new treatments for end-stage cardiac disease include gene therapy, surgical repair of damaged cardiac valves, or transcatheter valvular repairs.

Research is ongoing to improve our canine and feline patients’ surgical and nonsurgical therapeutic options in managing heart disease and CHF. Looking ahead, in addition to using a multi-modal approach to cardiac management that includes a pet’s diuretic regimens, we may augment therapy with different medication classes, improving afterload reduction, and using newer drug classes used in humans, such as sodium-glucose cotransporter-2 inhibitors and neurohormone-modulating medications.

Hopefully, we can improve our management of companion animal heart disease and outcomes once CHF develops. For now, we must look at current therapies and the research that exists to date on various drugs and indications for guidance and current recommendations.

Preserving the HAB

Gone are the days when we treat a heart murmur solely based on breed predisposition, age, and related factors. We want to treat only those patients that will benefit from treatment, gaining improved lifespan and health outcomes while doing no harm. We want to ensure we use the correct medications and, when possible, animal-labeled products.

Numerous updates to guidelines help direct our treatment paths for specific cardiac conditions. Several medications licensed explicitly for veterinary cardiac therapy and innumerable others, both veterinary and human-approved, are used off-label and remain key in our therapeutic arsenal when treating cardiac diseases in addition to knowing when, who, how, and with what to treat we want to know what is new and up and coming.

Now more than ever, generic drugs and drugs labeled with species-specific uses are paramount to improving our ability to deliver high-quality, evidence-based medicine while aiding in preserving the HAB.

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Erica Tramuta-Drobnis, VMD, MPH, CPH, is the CEO and founder of ELTD One Health Consulting, LLC. Dr. Tramuta-Drobnis works as a public health professional, emergency veterinarian, freelance writer, consultant, and researcher. She is passionate about One Health issues and believes pet health, food safety, agricultural health, and more can address the interconnection of human, animal, and environmental health.

References

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