Mary Allen
Mitral nocardiosis is the most common heart disease in dogs. Mitral insufficiency is often used as a synonym, which, strictly speaking, is not entirely correct.
Mitral nocardiosis is a degenerative disease of the connective tissue of the mitral valve (the atrial valve between the left atrium and left the main chamber), which causes the valve leaflets to “roll up”. Heart valves work as non-return valves, meaning they allow blood to flow in one direction and not the other. This function is partially lost when the valve leaflet rolls up, and the valve becomes leaky (or insufficient). This insufficiency, in turn, is of central importance for the progression of the disease and the development of clinical symptoms. In the final stage, blood accumulates in the lungs via the left atrium and pulmonary edema (“water in the lungs”) occurs. In the worst case, mitral valve endocarditis leads to left heart failure.
In addition to mitral endocarditis, there is often tricuspid endocarditis – i.e. a degenerative disease of the right atrial valve. In the advanced stage, blood can back up in the systemic circulation and consequently in the abdominal cavity (“ascites” or abdominal fluid) and chest (“thoracic effusion” or “pleural effusion”).
Which Dogs Get Sick?
As already mentioned, it is the most common heart disease in dogs, cats hardly ever get it. The disease first appears in the majority of cases in small dog breeds from the age of 7 to 8 years. An exception is the Cavalier King Charles Spaniel, which is often affected from the age of 1.5 – 2 years. Large dogs are much less likely to get sick than small breeds. Commonly affected dog breeds include:
- Cavalier King Charles Spaniel
- dachshund
- miniature poodle
- Yorkshire terrier
What Symptoms Does The Owner Notice?
Dogs in the early to mid-stage show no symptoms. By means of various control mechanisms, the body can usually compensate for the disease over a long period of time. From a certain point in time, however, the body can no longer manage this and decompensation occurs. From the moment of decompensation, clinical symptoms become obvious to the owner. The most common symptoms include:
- Cough
- Rapid breathing or shortness of breath
- Underperformance (only in the final stages)
- fainting spells
- End-stage emaciation
- Abdominal enlargement (only in tricuspid endocarditis)
The above symptoms are non-specific and can therefore be triggered by a variety of other diseases. Just because a patient has mitral valve endocarditis doesn’t mean their symptoms are automatically triggered by that condition!
Basically, if symptoms are caused by heart disease, they will continue to worsen over a short period of time.
Therefore, a cardiac cough that is not treated appropriately will become progressively worse over a few days or a few weeks and eventually lead to rapid breathing and even shortness of breath.
Heart-related symptoms always show a tendency to worsen – as long as there is no adequate therapy.
Cough, which occurs sporadically from time to time, can therefore not be caused by an underlying cardiac disease. The same applies to panting, which occurs again and again and disappears by itself.
Symptoms are only noticed by the owner at a late stage, the disease worsens over a long period of time without showing any symptoms!
Many owners are surprised when their dog suddenly shows shortness of breath as a result of mitral endocarditis because until then they had not noticed any changes in their animal!
What Causes Endocarditis?
Endocarditis refers to degenerative changes in the heart valves. The exact trigger is not yet known. Inflammation of the heart valves used to be the cause for a long time, but this theory has been refuted for a long time. It is probably a genetic event, which is also suggested by the frequent occurrence in certain small dog breeds such as the Cavalier King Charles Spaniel. Ultimately, the structure and composition of the connective tissue of the mitral and/or tricuspid valve and their appendages change. Layers of connective tissue loosen their bond, causing the valve to “roll-up” and its often characteristic club-like appearance on ultrasound. At the same time, some of the suspension ligaments of the heart valves (“chordate tendineae”) can tear, resulting in a prolapse, i.e. a “punching through” of the respective valve. This will further aggravate an existing leak. As already described, endocarditis actually only affects the two atrioventricular valves, i.e. the mitral and tricuspid valves. The mitral valve alone is affected in 60% of cases, the tricuspid valve in 10%, and both valves in 30%.
How Is The Disease Diagnosed?
A preliminary diagnosis can often be made on the basis of the clinical examination by means of listening (“auscultation”), during which a heart murmur is noticed. However, the heart murmur usually does NOT allow any conclusions to be drawn about the severity of the disease! In conjunction with an X-ray, however, you can already get a good impression of the degree of severity. However, the most accurate diagnostic tool is the heart ultrasound including a Doppler examination. Here the individual chambers can be measured very precisely and the morphology of the valves can be assessed. The Doppler examination also makes it possible to display and quantify the return flow of blood. Furthermore, statements can be made here about the pumping function of the main chambers and about intracardiac filling pressures.
How Is The Disease Progressing?
The disease usually progresses relatively slowly. Patients with mitral nocardiosis should be monitored regularly in order to be able to better assess the course of the disease and to be able to intervene therapeutically if necessary. There are often several years between the first detection of the disease and the appearance of clinical symptoms. However, this cannot be generalized to every patient. Large dogs in particular are an exception, insofar as the disease progresses much faster here. If a patient is in the terminal stage with water in the lungs (“pulmonary edema”), the survival time is often less than a year.
Is There A Chance Of Recovery?
Unfortunately, no. The disease can only be treated symptomatically, with the focus here being on improving the quality of life. Fortunately, many patients become ill at a relatively old age, so that they never develop symptoms due to the often rather slow progression of the disease. A surgical therapeutic approach (valve repair) is theoretically possible but has hardly played a role in veterinary medicine due to the immense costs.
What Therapy Options Are There?
There is currently a great deal of confusion on this subject. For a long time, it was customary to treat patients with ACE inhibitors or digitalis preparations solely on the basis of a wiretapping finding. This practice is now obsolete. Before starting therapy, the stage of the disease must be determined by means of an X-ray or, even better, an ultrasound, because the further therapeutic procedure depends on this.
The following stages can be distinguished:
- A: Patient at risk: the dog is not ill, but is one of the predisposed breeds (e.g. small, old dog, Cavalier King Charles Spaniel)
- B1: Asymptomatic dog (or dog with symptoms not related to heart disease) with the valvular disease without enlargement of the heart
- B2: Asymptomatic dog (or dog with symptoms not related to heart disease) with the valvular disease with enlargement of the heart
- C: Symptomatic dog in congestive heart failure (pulmonary edema) due to valvular disease
- D: Symptomatic dog in refractory congestive heart failure unresponsive to standard therapy
Stage A
no therapeutic approach
Stage B1
Dogs without an enlarged heart do not need therapy. This seems incomprehensible to many owners at first, since their animal suffers from heart disease, which is not treated. However, just like in human medicine, there is currently no drug that can positively influence the course of the disease at this stage.
Stage B2
In the meantime, however, there is an effective therapy for dogs from a moderate stage in which there is an enlargement of the heart. In one of the largest veterinary cardiology studies to date, pimobendan has proven to be very effective. The drug leads to a reduction in the size of the heart muscle and a significant extension of the symptom-free time. Pimobendan is therefore the drug of choice for patients with enlarged hearts.
Stage C
Decompensated patients with pulmonary edema are treated with a combination of drainage drugs (“diuretics”, furosemide or torasemide) and pimobendan. The blanket use of ACE inhibitors such as benazepril or enalapril or the mineralocorticoid antagonist spironolactone must be critically questioned and should be decided on a case-by-case basis.
Sometimes there are secondary cardiac arrhythmias, which then have to be treated with an antiarrhythmic, depending on their severity. In contrast to human medicine, additional anticoagulant therapy is not necessary for dogs. As with almost all other heart diseases, once therapy has been started, it must be continued for life in almost every case.
Stage D
In addition to the drugs mentioned in stage C, other diuretics such as hydrochlorothiazide or spironolactone can also be considered here. Sometimes it is also useful to lower blood pressure with amlodipine.
The scheme below is a brief summary of current studies and international expert opinions on the general therapy recommendation for mitral endocarditis. In individual cases, however, it may be necessary to deviate from the therapy scheme given here.
Is It Sensible/necessary To Change The Diet?
A change of diet can be useful in patients with very advanced findings, earlier it is probably of little benefit. Salty treats should be eliminated from the diet of a severely ill animal. Likewise, a mild, low-salt, higher-energy diet can help reduce the severity of symptoms and ensure adequate energy intake. One problem, however, is that our pets often reject low-salt diets. Then it is always better to offer some favorite diet than to insist on a “heart diet” that the dog does not eat, otherwise the patient’s energy needs cannot be met. In severely affected animals, the use of omega-3 fatty acids can also help.
It is important to note that contrary to popular belief, patients with advanced heart disease should NOT lose weight. Weight loss leads to increased mortality in critically ill cardiac patients. Weight reduction to “relieve the cardiovascular system” is wrong in animals with advanced disease!
Do Electrolytes Such As Potassium Or Magnesium Have To Be Supplemented When Treated With High-Dose Dehydration Drugs?
Usually no. A patient who drinks and eats normally does not usually need additional electrolytes such as potassium or magnesium. The role of magnesium in veterinary medicine has not yet been clearly clarified, since the magnesium level in the body is difficult to measure, and conventional blood tests are usually too imprecise for this. The role of magnesium could lie in the treatment of therapy-resistant arrhythmias, which can occur in the context of mitral endocarditis. However, a basic therapy with magnesium should be avoided, since many patients with diarrhea react to the electrolyte.
My Dog Is Being Treated With Dehydration Medication. Should I Limit His Water Consumption?
Only a short answer is necessary here: in no case!
What Can You Do As The Owner Of A Sick Patient?
Especially patients in advanced stages of the disease require special attention from the owner. Especially in animals with previous pulmonary edema, it is extremely important to pay attention to an increasing cough and to regularly count the respiratory rate of your patient. This should not be more than 45 breaths per minute at rest (important: do not count after exertion, this automatically increases the heart rate). It is also important to recognize trends. If the respiratory rate increases – for example, you count 20/min in the morning, 40/min at noon, and 50/min in the afternoon – this can indicate the onset of pulmonary edema and you should contact your veterinarian as soon as possible.
Do I Have To Take Care Of My Dog?
For the vast majority of heart diseases, the basic rule is that affected animals are allowed to exercise within the framework that they offer themselves. Sick dogs are allowed to exercise normally, but if they want to take a break from training, this must be accepted.
However, very intense training or training in high heat should be avoided in animals with severe findings. If in doubt, your cardiologist should be able to provide you with information.