What is Heart Block (Complete)?
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 ventricles to the atria and vice versa. A normal heart rate can fluctuate from 60 to 175 beats per minute, but with complete heart block, your dog’s heart rate can drop below 40 beats per minute, causing fainting, collapse, or sudden death. It is a life-threatening emergency, so if your dog’s heart rate is lower than 50 beats per minute you should get to the emergency animal hospital or see your veterinarian immediately.
Third degree heart block, or complete heart block, occurs when the upper (atria) and lower (ventricles) heart chambers are blocked so badly that the electrical impulses are not getting through at all. This does not mean that the blood is not flowing to the heart, it is the electrical impulses that are not getting through. When this happens, there is a pacemaker in the lower heart chambers that will take over until the heart block is repaired. However, the heart rate may drop extremely low (below 40 beats per minute), which can be fatal if not treated immediately.
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Symptoms of Heart Block (Complete) in Dogs
Often, there may be no obvious signs of heart block besides tiredness, which you may not notice. However, some of the most often reported symptoms are:
- Loss of appetite
- Weight loss
- Acting weak or sleepy
- Pale or blue tint to gums and tongue from low oxygen levels
- Breathing troubles (too fast or too slow)
- Inability to exercise
- Very slow heart rate (below 50 beats per minute)
- Swelling of the abdomen due to fluid build-up
Causes of Heart Block (Complete) in Dogs
Although first and second-degree heart block can be caused by nothing but a vitamin deficiency or intense exercise, a complete heart block almost always has an underlying condition that needs treatment. Some of the most common causes are:
- Bacterial infection
- Birth defect
- Cancer (amyloidosis or neoplasia)
- Certain breeds, such as the Pug, Cocker Spaniel, and Doberman Pinscher
- Chagas Disease
- Duchenne muscular dystrophy
- Electrolyte imbalances
- Endocarditis (swelling of the lining of the heart)
- Golden Retriever muscular dystrophy
- Heart attack
- Hyperkalemia (too much calcium in blood)
- Hypertrophic cardiomyopathy
- Ingestion of certain drugs, such as digitalis
- Lyme disease
- Myocarditis (heart inflammation)
- Polymyositis (chronic inflammatory muscle disorder)
- Scarring of the heart from an unknown cause
Diagnosis of Heart Block (Complete) in Dogs
Because a complete heart block is a life-threatening emergency, you should take your dog immediately to an animal hospital or clinic if you cannot get an immediate appointment with your veterinarian. However, let your veterinarian know where you are going and give the name and number of your veterinarian to the animal hospital. The veterinarian will first need to get your dog stabilized before performing an examination or tests. This may include draining any fluid built up in the abdomen by abdominocentesis, oxygen, and IV therapy.
Once your dog is stable, you need to provide the veterinarian with as much information as you can about what led up to the symptoms you have seen. They will also need information about previous illnesses and injuries, shot records, and any changes in behavior or appetite you have noticed.
The veterinarian will then examine your dog thoroughly and check vital signs, weight, height, heart rate, and respiration. He will pay special attention to the heart rate, and will probably hook your dog up to an ECG machine at this point to get an electrocardiogram. This is a recording of the heart’s electrical impulses which is performed by attaching electrodes to your dog’s knees and elbows. The test is not painful and your dog will not feel anything unusual during the procedure. Another test that can help determine the cause of the heart block is an echocardiogram, which is an ultrasound of the heart that gives the veterinarian the ability to see inside your dog’s chest and see the heart walls, valves, and chambers. Some blood tests will be done as well, such as a CBC, blood gas, and chemical panel.
Treatment of Heart Block (Complete) in Dogs
No matter what the cause, surgery will probably need to be done to insert a pacemaker to keep your dog’s heart beating at the right pace. The veterinarian may prescribe medication, such as propranolol or atenolol.
Recovery of Heart Block (Complete) in Dogs
If your veterinarian does not think your dog is well enough to make it through the surgery, he may not want to insert a pacemaker. The veterinarian may choose to give medication and see if your dog’s condition improves enough for surgery. However, without a pacemaker, your dog’s prognosis is not good. With a successful pacemaker implantation, your dog can live a relatively normal life, although you will have to see the veterinarian for regular check-ups.
Heart Block (Complete) Questions and Advice from Veterinary Professionals
I have a 2 year old male chihuahua who was diagnosed with Stage 3 AV. Occasionally, he coughs. No other underlying disease(s) found. Is it really worth putting him through the stress of surgery, recovery, and altered life with a pacemaker? It is not the cost I am concerned about, but the quality of his life after PM insertion. I have 2 other dogs, much bigger than him, and he will need to be kept away from them and kept calm, at least through recuperation. Love to know your thoughts, as he is so young.
Pacemaker placement is the treatment of choice for third-degree atrioventricular block; I am not so familiar with pacemaker implantation and use and therefore would recommend visiting a Cardiologist to give you more information and guidance regarding pacemakers and recovery. I have added some links below for your information from reputable sources. Regards Dr Callum Turner DVM
My 3lb yorkie has a pacemaker since July 7th was never ever sick she’s 9years old the recuperation was not bad and hers was done I. Her stomach in side as she is to small to have it in neck so far so good on Meds every 12 hours 3 in am 4 in pm a d doing so far ok back for recheck nov 9th at University of Florida
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My 12 yr old dachshund was just diagnosed with Heartbock Type 2. She is very tired all the time, no longer real interested in food, and she no longer plays with toys or chews on bones. All this showed up rather suddenly in a two week period. My vet said there is nothing to do. Is there no medicines to help? Vet does not feel she will survive a surgery. I hate to see her so inactive and unengaged in life now.
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