Heart Inflammation (Myocarditis) in Dogs

Your dog’s heart is the most important organ in the body, keeping the other organs and the rest of the body pumped full of fresh, oxygenated blood. If there is something wrong with your dog’s heart, everything in his body will suffer. Just like with a motor in a vehicle, the heart is the main pump that keeps everything moving the way it should so when there is a problem in the heart, your dog’s other organs will be affected as well. Heart inflammation (myocarditis) causes the heart to swell and will slow the rest of the body down, causing symptoms that can mimic many other illnesses. It is because of this that myocarditis is rarely able to be diagnosed until it is too late. That is why it is essential to take your dog to the veterinarian regularly and whenever they are acting “different than usual” because you are the best judge of what is “normal” for your dog.

Heart inflammation (myocarditis) is a cardiac disease in dogs caused by the swelling of the heart muscle. Often, there are no symptoms with myocarditis until it gets severe enough to cause heart failure, at which time it causes weakness, difficulty breathing, coughing, and heart arrhythmia among other symptoms. There are many causes, but the most common causes are viral diseases, fungal, bacterial, protozoan infections, mineral deficiency, injury, or exposure to toxins. It is difficult to find the exact cause of myocarditis in dogs since the only way to prove the dog has myocarditis is a histopathological examination from a heart biopsy sample or from a post-mortem examination.

Symptoms are relatively similar, but some may differ slightly with each cause:

Lyme Carditis

• Fever
• Lethargy
• Not eating
• Lameness of one or more legs
• Swelling of the joints
• Joint pain
• Skin lesion from the tick bite
• Lymphadenopathy
• Heart block
• Endocarditis

Canine Parvovirus

• Vomiting
• Diarrhea
• Weakness
• Elevated temperature (to 106 degrees or more)
• Coughing
• Abnormal heart rate
• Heart murmur
• Difficulty in exercising
• Breathing problems
• Fainting spells
• Collapse
• Loss of appetite
• Weight loss
• Water retention (edema)

West Nile Virus

• Cough
• Weakness
• Fever

Mineral Deficiency (i.e. copper, iron)

• Gradual weakness
• Coughing
• Sleepiness
• Appetite and weight loss

Acute and Chronic Trypanosomiasis (Chagas' disease)

• Vomiting
• Diarrhea
• Coughing
• Fever
• Weakness
• Extreme sleepiness
• Lack of energy
• Swollen abdomen
• Inability to exercise or walk for long period

Ischaemic Heart Disease

• Coughing at night
• Coughing during exercise
• Rapid breathing
• Fainting
• Weakness
• Swollen abdomen

Physical Injury/Exposure to Toxins

• Usually no symptoms until collapse

 Types

Infectious Myocarditis include any kind of infection, bacteria, or fungus such as Lyme carditis, canine parvovirus, and Chagas’ disease.

Non-infectious Myocarditis includes Ischaemic heart disease, mineral deficiency, physical injury and exposure to toxins rather than an infection, bacteria, or fungus.

• Lyme carditis (from a tick bite)
• Canine parvovirus (three to nine weeks old)
• West Nile virus
• Trypanosomiasis (Chagas' disease)
• Ischaemic heart disease
• Mineral deficiency (i.e. copper, iron)
• Injury
• Exposure to toxins

Your veterinarian will perform a complete physical examination including blood pressure, body temperature, and heart rate. He will be particularly interested in listening to your dog’s heart rate to check for irregularities, murmurs, and arrhythmias. You will need to provide your veterinarian with your dog’s complete medical history, including any recent illnesses or changes in behavior. The veterinarian will have to run some tests, such as:

• Complete Blood Count (CBC)
• Blood chemistry panel
• Blood gases
• Urinalysis
• Digital radiographs (x-rays) of the chest and abdomen
• Electrocardiographic examination (ECG)
• Echocardiographic examination (Echo)

If the veterinarian finds an abnormality, your dog will have to wear a Holter ECG Monitor for 24 hours to determine exactly what is causing the issue. The Holter is just a portable heart monitor that the veterinarian will strap securely onto your dog to wear at home for 24 hours. Here are some cause-specific tests that may need to be done:

• Lyme disease carditis – Increased antibody titre
• Canine parvovirus – Elevated antibodies
• Trypanosomiasis (Chagas’ disease) – Shows up in bacterial or serum culture

The veterinarian will first make sure your dog’s heart is stable, and will do what is necessary to improve the strength of the heart muscle, control arrhythmia, and prevent the fluid from building up in the lungs and abdomen. Specific treatment will depend on the underlying cause of the myocarditis:

Lyme carditis is treated with antibiotics, such as penicillin. Canine parvovirus is a serious disease that requires hospitalization and IV fluids. This illness can be fatal for many dogs and the only way to prevent parvovirus is vaccinations when your dog is young. West Nile virus is also serious and will often require hospitalization and IV fluids but it is quite rare in dogs. Trypanosomiasis (Chagas' disease) has no cure, although some veterinarians use Benznidazole to help control the progression of the disease.

Ischaemic heart disease is commonly treated with one or more of these medications:

• Ace inhibitor (Enalapril)) to decrease the stress on the heart
• Beta blocker (Atenolol) to lower blood pressure
• Vasodilator (Nitroglycerin) to dilate the veins
• Digitalis (Digoxin) to slow the heart rate
• Diuretic (Lasix) for fluid retention

Mineral deficiency is treated with vitamin and mineral supplements. Injury or exposure to toxins are treated with hospitalization to treat the injury or remove as much of the toxin as possible.

The recovery rate for your dog varies depending on the cause of the myocarditis, how soon you get treatment, and how well your dog responds to treatment. Some veterinarians advise adding taurine and carnitine to your dog’s food. With good medical care and regular visits to the veterinarian, your dog can live for more than a year after diagnosis. Be sure to keep your follow-up appointments and give medication as prescribed by your veterinarian.