What is Heart Block (Mobitz Type 1)?
Your dog’s heart is similar to your own, having four chambers, which are the two atria on top and two ventricles on the bottom. When the upper heart chambers are not communicating well with the lower chambers, the body (left ventricle) and lungs (right ventricle) are not getting enough blood, this is a condition called heart block (AV block). There are four types of heart block, which are first degree, second degree (Mobitz type I), second degree (Mobitz type II), and third degree (complete heart block). This disorder happens due to the electrical impulses not being able to get from the atria to the ventricles. Mobitz type I heart block is similar to first degree heart block except the length between heartbeats gets longer each time until it skips, and then it starts over again. This means that your dog’s heart will beat slower and slower until it misses a beat, causing dizziness or faintness. This type of heart block is actually found most often in young, healthy dogs because of their high vagal tone.
Second degree heart block has two types, Mobitz type I and Mobitz type II, which are both serious conditions, although type I is the more common, but less serious type. In second degree heart block, some of the electrical signals from the heart are not communicating with each other as they should, which causes the heart to skip some beats and slow down the heart rate. This is commonly found in healthy dogs, and although it is not as serious as Mobitz type II heart block, it can still be serious if the underlying cause is not found and treated.
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Symptoms of Heart Block (Mobitz Type 1) in Dogs
When second degree type I heart block is caused by increased vagal tone (normal abnormal), there are usually no symptoms at all. Although many affected dogs do not seem to have any symptoms or warning signs, there are some that can get dizzy, weak, and may even faint. The symptoms rely completely on the underlying cause of the type I heart block, if there is a cause.
If the heart block is brought on by medication the symptoms can include:
- Loss of appetite
If the cause is an unrelated disease or illness, the symptoms will depend on which disease or illness is involved.
- Appetite loss
- Breathing difficulty
- Nasal discharge
- Abdominal pain and swelling
Causes of Heart Block (Mobitz Type 1) in Dogs
The most often reported cause of second degree type I heart block is an increased vagal tone, which is actually normal in young, healthy animals and no cause for concern unless it causes symptoms that are concerning. This condition usually clears up on its own in time and may occur in normal, healthy animals. Here are some other common causes:
- Accidental ingestion of certain medications
- Illnesses or diseases that are not related to the heart, but can cause type I heart block
- These can be neurological, respiratory, or gastrointestinal and will continue causing symptoms of type I heart block until the illness is treated
Diagnosis of Heart Block (Mobitz Type 1) in Dogs
Since there are usually no symptoms that are directly related to the abnormal heart rate, many times the heart block diagnosis is made during an unrelated examination. In fact, you may have brought your dog to the veterinarian for the symptoms of the illness that caused the heart block in the first place. Be sure to let your veterinarian know if your dog has recently been exposed to other dogs that may have been ill, such as at a dog park or doggy day care. This can be an important factor if the cause is a contagious illness. The veterinarian will give your dog a thorough physical examination, check vital signs, listen to your dog’s heart, and get some blood and urine to perform some laboratory tests. Some of the tests may include a complete blood count (CBC), blood chemical panel, blood clotting test, and urinalysis.
The veterinarian will probably do an electrocardiogram (ECG) to get a reading of the electrical impulses of your dog’s heart as well as a cardiac ultrasound (echocardiogram) to see the movements of the heart’s chambers. These tests should be able to give the veterinarian an idea of which degree and type of heart block your dog has, if any. He may also want to send you to see a veterinary cardiologist for more tests.
Treatment of Heart Block (Mobitz Type 1) in Dogs
The treatment depends on the cause, as it usually does. In the case of medication toxicity, the medication should be stopped or dosage should be changed. If it is caused by an underlying illness, that will need to be treated according to the nature of the illness. Most often though, there is no need for treatment as it is usually due to natural causes.
Recovery of Heart Block (Mobitz Type 1) in Dogs
As with any illness that has to do with a vital organ such as the heart, regular follow-up examinations must be done regularly to be sure the heart block does not return. Be certain to contact the clinic if you see any changes in your pet's behavior or health condition.