Ron Hines DVM PhD
In large dogs younger than 10 yrs of age, dilated cardiomyopathy (DCM) is the most common cause of heart disease leading to death. In the general dog population, DCM ranks only behind mitral heart valve disease and congestive heart failure (CHF) as an eventual cause of mortality.
A diagnosis of dilated cardiomyopathy puts enormous emotional strain on a dog owner. Unlike congestive heart failure (CHF) for which your veterinarian has many medical treatment options, veterinarians like myself must inform you that we have very limited ways to buy more time for cardiomyopathy dogs. Costly open heart surgery is sometimes even an option for heart valve problems. ( read here ) , but not for cardiomyopathy. Conveying that news is the hardest part of my being a veterinarian. You can read how that grief affects us all here.
What Is Occurring When DCM Affects My Dog’s Heart?
In dogs that develop dilated cardiomyopathy, changes have occurred in the cardiac muscle that composes their heart that decrease the organ’s ability to forcefully contract. Although those changes are generally present in all of your dog’s four heart chambers, they are usually most severe in the lower left chamber, the left ventricle. That chamber is the most muscular of the four because its job is to force blood throughout your dog’s entire circulatory system of arteries and veins. When it can no longer do that efficiently, blood pools (congestion) in the pet’s lungs and various other organs and body cavities (eg ascites , pulmonary edema). As the dog’s heart struggles to meet its body’s circulatory needs, its walls become thinner, the heart’s size enlarges (=dilation) and the heart assumes a more rounded (globular) shape.
Are Certain Dog Breeds More Susceptible Than Others?
Your dog’s individual genetics are thought to account for a great deal of its susceptibility to dilated cardiomyopathy. I already mentioned that the larger dog breeds face DCM considerably more frequently than smaller dog breeds. But even large breeds do not suffer the problem with equal frequency. Of the 11 breeds most likely to develop DCM in one Stockholm study, Great Danes, St. Bernards, Newfoundlands, Leonbergers, Dobermans, Finnish hounds, Boxers, Giant Schnauzers, English cocker spaniels, and Flat-coated retrievers led the list in DCM frequency. Others put Irish Wolfhounds at the top of susceptibility. Dogs are usually, but not always, middle-age when conspicuous signs of the disease first appear. In the same Stockholm study, the median survival time for all dogs after the disease had been diagnosed was 27-140 days. I will send you the study if you request Haggstrom2008.pdf. Even within those higher-risk breeds, some families, kennels and genetic lines are considerably more likely to develop dilated cardiomyopathy than others. It is only when the gene pool of a breed is dangerously small (too few originating dogs or “progenitors”) that the whole breed tends to suffers. That seems to be the case in Irish Wolfhounds. (read here) According to Purdue University Veterinary School statistics, the prevalence of DCM in male dogs examined in their clinic was nearly twice that of females (0.66% vs 0.34%).
Why Do Dogs Develop Dilated Cardiomyopathy – What Is Going On In My Dog’s Heart ?
As I mentioned, veterinarians believe that certain gene combinations present in large dogs predispose them to DCM. If lifestyle, nutrition or other unknown factors increase the risk of large dogs developing the disease is still unclear. But there is a group of dogs for which veterinarians are quite suspicious that nutrition does play a part. That is generally when dogs of smaller breeds that are not known to carry a DCM tendency develop cardiomyopathy. I’ll get to that under Nutrition. In all forms of DCM the heart muscle (the myocardium) and the nerve fibers within the heart are damaged. In some cases, nerve damage (“attenuated wave fibers”) occurs first. In those dogs, heart rhythm defects occur before heart muscle damage is severe. In other cases, it is the reverse. With time, the size of the surviving individual heart muscle cells increase in an attempt to compensate for the muscle cells that have been lost. When that process is no longer adequate (volume overload) the walls of the heart chambers begin to stretch and thin. Space formerly occupied by healthy heart muscle cells is replaced by scar tissue (fibrosis). The amount of inflammation that accompanies this process is variable. A recent Russian study in dogs associated DCM with immune-mediated inflammation that attacks the heart’s electrical system. (read here) The changes reported in the study were real. But it is hard to separate cause from effect. If, in fact, the dog’s immune system was an underlying cause of DCM, medications that affect the immune system might be helpful. But it is just as likely that a failing heart was what caused those immune system changes.
If My Dog Develops Dilated Cardiomyopathy What Signs Might I See?
Dogs who are genetically predestined to develop DCM probably have destructive changes occurring in their hearts at an early age. But your are quite unlikely to notice them. The heart is a powerful organ created with a large reserve of muscle cells. For many years, it can often compensate for the loss of muscle fibers.
The first signs many dog owners notice is a decrease in their pet’s activity level. The dogs don’t have the willingness to exercise as much as they used to. Their heart can no longer meet the increased oxygen needs of strenuous exercise. Some loose weight due to their poorer appetite. In breeds with a high incidence of DCM, even those subtle signs might prompt your veterinarian to have some electrocardiogram tests run – probably with a Holter halter.
But in most cases, early signs of DCM are overlooked and it is not until signs attributable to heart failure occur that these dogs are brought to their veterinarians. The signs then generally include coughing, a rapid irregular and weak pulse, rapid and difficult breathing (dyspnea), pronounced weight loss, and sometimes, fluid accumulation in their abdomen (ascites). Other dogs experience fainting spells due to disturbances in their heart’s electrical system. Their gums are often pale and the tiny blood vessels in the gums more prominent (injected). Their heart beat can often be detected in their jugular vein (jugular pulse). ( read here )
Some breeds, such as standard schnauzers with DCM, tend to go on to heart failure at an earlier age (~1.6 years) – particularly males. Sometimes the progress of DCM is rapid enough for a dog to die from an irregular heart beat before it was even noticed that they were ill.
What Test Will My Veterinarian Need To Run To Confirm That DCM Is My Dog’s Problem?
Your veterinarian will quickly zero in on your dog’s heart as is probably problem. But there are a number of other heart diseases that can produce the same clinical signs. As I mentioned, all forms of heart disease produce quite similar symptoms; and other problems like pneumonia, chest tumors, toxin ingestion, heart developmental defects and autoimmune disease can produce similar heart-related symptoms too. I live in South Texas where Chagas disease in dogs also mimics DCM. ( read here ) This disease and the kissing bug parasites that spreads it are slowing moving northward into the United States. (read here)
Once DCM has progressed to heart enlargement, x-rays of your dog’s chest will indicate that. Those x-rays will also help rule out some of the other causes of difficult respiration that I mentioned. An irregular pulse and heart murmurs detected with a stethoscope in non-anemic dogs help confirm heart involvement. If there is doubt, a proBNP test might be ordered as well.
At that point, your veterinarian will probably let you know that a board certified veterinary cardiologist has the specialized training required to delve deeper into your dog’s heart problem. Their tools are doppler ultrasound (echocardiography) that examines the thickness of your dogs heart chambers, abnormal distortions and the flow of blood through the heart. ( read here ) Veterinary cardiologists also have more experience utilizing some of the specialized medication cocktails in ways more likely to minimize side effects.
They closely examine your dog’s electrocardiogram– the electrical signals that fire the dog’s heart contractions on every beat. That might be done with a 24-hour Holter monitor ECG recording device. Rhythm defects are one of the main things cardiologists are looking for (eg atrial fibrillation, supra-ventricular tachycardia ventricular premature complexes and ventricular tachycardia). All predispose a dog to sudden death.
Your veterinarian and/or the cardiology specialist might suggest some genetic tests to determine if a dog carries gene combinations that predispose it to DCM – particularly if you are selecting the dog for breeding or as a service dog or tests that detect telltale compounds an inapparent but damaged heart might release such as proBNP or natriuretic peptide. Most of these tests are still in their developmental stage. ( read here )
Other than the proBNP or natriuretic peptide tests and confirmation that hypothyroidism is not compounding your dog’s problem, blood serum chemistry and urine tests ( read here ) do not give much insight into organic heart problems – but your vet may want to run them just to be sure there are no coexisting liver, kidney or other problems that might affect the action of the heart medications he/she will dispense.
Veterinarians have known for a long time that a taurine sulfo-amino acid deficiency can be responsible for dilated cardiomyopathy in cats. ( read here ) Turkey and chicken are particularly rich in taurine, as are shellfish. In dogs, carnitine deficiencies were once implicated in heart failure as well. ( read here ) But more recent studies have not confirmed that. With time, the prevalence of DCM in cats decreased as pet food manufacturers made sure that their diets contained sufficient amounts of taurine after processing (good meat is expensive so some manufacturers add industrially-produced taurine) . Cases of taurine deficiency-induced DCM have also reported in dogs – particularly golden retrievers. ( read here )
The incidence of DCM in which diet is suspected of playing a factor has been creeping up. That increase has paralleled the trend to feed dogs higher priced dog foods that base their acceptance on being grain-free or containing exotic ingredients. They are often among the “boutique premium brands” with trendy ingredients. There is more profit in selling these products than in selling traditional dog food, so many small companies manufacture them and sell them through groomers, pet superstores, the internet and the like. But these smaller companies rarely have veterinary nutritionists on staff or the resources for sophisticated nutritional analysis. Even the larger dog food manufacturers see financial opportunities in providing these untested products.
It may not be that these dog foods are deficient in taurine. But their formulas – especially the ones that advertise as “grain-free” – might in some way decrease taurine absorption. Many of these diets claim to meet the canine nutritional standards of the AFIA , a pet food trade association. But few if any were ever tested in dog feeding trials that observed for later heart or other disease issues. Your vet might suggest a blood taurine level test. But taurine supplementation – even with confirmed low taurine levels – does not necessarily revere the damage that DCM has already caused.
What Are My Dog’s Treatment Options?
The best your veterinarian has to offer your dog are medications that might improve the remaining abilities of its heart to pump blood. Those are the same drugs that veterinarians use to treat all forms of heart failure in dogs. (ref)
Those medications include ACE inhibitors like enalapril and benazepril to lower resistance to blood flow. They also include pimobendan (Vetmedin®) to strengthen the force of each heart contraction. When the dog’s heart is no longer pumping forcefully enough to keep fluids from pooling in the lungs and abdomen, furosemide (Lasix®), a diuretic, is usually dispensed. One of these heart drugs, pimobendan, appear to gain more time for your dog when DCM is discovered early. More exotic medications like carvedilol and metoprolol and drugs given in an attempt to correct heart rhythms such as mexiletine, atenolol and sotalol are sometimes given by veterinary cardiologists as well. When furosemide no longer suffices to control pooled fluids in your dog’s lungs or abdomen, other diuretics such as spironolactone and hydrochlorothiazide can be added as well.
Some veterinarians dispense l-carnitine, taurine, omega-3 and Coenzyme Q supplements. But none have been proven to be of help other than those containing taurine (when blood taurine levels were confirmed to be low). Both Hills and Purina make low-sodium dog foods. But none have been confirmed to extend the lives of dogs with DCM.
What Is The Outlook For My Dog?
That varies from case to case but the end result is never favorable. Some breeds, like dobermans tend to go down hill rapidly – even with medications. Others, like cocker spaniels often go down hill slower. The outlook for dogs improves slightly when their heart is enlarged but no electrical (rhythm) abnormalities are detected. The only cases of DCM that have occasionally been reversed or halted are those that were due to a taurine deficiency that was corrected. Very few dogs survive more than 6 months to 1.5 years after a diagnosis of DCM has been made.
Can We Predict Which Dogs Will Develop DCM When Purchasing A Puppy Or Selecting A Breeding Dog?
When contemplating the purchase of a high DCM risk breed, exhaustive research into the dog’s parents and their siblings for evidence of increased susceptibility (family history) to DCM is desirable. Some breeders go so far as to schedule yearly echocardiogram and Holter monitor screening of their breeding dogs. Prospective dog owners need to be certain that the family line from which their dog is selected was not prone to early death – regardless of the reported diagnosis. That is the sort of information that some breeders are very reluctant to release.
There has been some progress in finding genes that are associated with doberman pinchers developing cardiomyopathy later in life. ( read here ) The problem is that some dogs that carry these genes will never develop heart disease (= incomplete or variable gene penetrance) while others that appear free of those genes still develop cardiomyopathy (DCM). Others are looking for blood tests that might be specific for compounds released early in the dilated cardiomyopathy disease. ( read here ) Genetic tests for DCM in specific breeds are also available. ( see here )