Heart Block (Mobitz Type II) in Dogs: Symptoms, Diagnosis, and Treatment
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A heart block in dogs occurs when the electrical signal that travels through the heart is delayed or stopped. This disruption in the signal can lead to changes in the heart rhythm or dropped beats. While some heart blocks are minor, others can be very dangerous.
Key Takeaways
- Mobitz Type II is a second-degree heart block that occurs when some of the heart’s electrical signals fail to reach the ventricles.
- Some dogs have no symptoms, while others may develop a slow heart rate, weakness, exercise intolerance, collapse, or fainting.
- Treatment depends on the cause and severity of the heart block; some dogs need monitoring and treatment of an underlying condition, while more severe cases may require a pacemaker.
- Dogs with Mobitz Type II need veterinary monitoring because the heart block can persist or progress to a more serious conduction abnormality.
What Is Heart Block (Mobitz Type II) in Dogs?
Mobitz Type II heart block is a type of second-degree atrioventricular (AV) block in dogs. It occurs when some electrical signals fail to travel from the heart's upper chambers (atria) to the lower chambers (ventricles), causing skipped heartbeats and a slower heart rate.
An electrocardiogram (ECG) is used to diagnose a heart block.
Dogs with Mobitz type II heart block may have no symptoms, but more severely affected dogs can develop weakness, exercise intolerance, collapse, or syncope (fainting).
If your dog faints, seek veterinary care immediately.
Symptoms of Heart Block (Mobitz Type II) in Dogs
Symptoms of heart block (Mobitz type II) in dogs include:
- Bradycardia (slow heart rate)
- Lethargy
- Exercise intolerance
- Syncope (fainting)
- Weakness
Some dogs with mild Mobitz Type II block show no symptoms at all.
Causes of Heart Block (Mobitz Type II) in Dogs
Heart blocks in dogs can occur following conditions that damage or change how well the heart’s electrical conduction system functions.
Senior dogs can develop heart blocks following age-related degeneration and hardening of the tissue in the heart around the conduction system. These sclerotic changes can interfere with electrical signaling.
Sometimes dogs develop this condition following an infection that leads to inflammation or damage to the heart. This can be seen with bacterial infections, including Lyme disease, which can cause inflammation of the heart muscle.
Primary heart disease can also lead to damage to the conduction system. Dilated cardiomyopathy and heart-based tumors may be associated with AV block.
Medical conditions that alter the electrolytes or minerals involved in contraction of the heart can also affect the electrical signal in the heart. Potassium and calcium are very important for the heart muscle.
Diseases that cause significant metabolic or electrolyte abnormalities—such as Addison’s disease and diabetes—can interfere with conduction and contribute to heart blocks.
Certain medications can also interfere with heart rate and electrical conduction.
Dogs may get into their humans’ medication or ingest too much of their own prescribed medication, leading to heart blocks.
Calcium-channel blockers, beta blockers, and digoxin can all interfere with AV conduction and may contribute to second-degree heart block.
How Veterinarians Diagnose Heart Block (Mobitz Type II) in Dogs
AV blocks are diagnosed using an ECG (short for electrocardiogram, also referred to as an “EKG”).
Your vet will likely start with a thorough examination. They will listen to your dog’s heart with a stethoscope.
If any abnormalities are noted, such as an abnormally slow heart rate or dropped beats, a cardiology consultation may be recommended.
Blood work, blood pressure measurements, and X-rays may also be recommended to screen for abnormalities.
Your dog may be referred to a veterinary cardiologist for imaging of the heart (called an echocardiogram) in addition to a complete ECG.
Sometimes Mobitz Type II heart blocks are detected while a dog is sedated or under anesthesia.
ECG monitoring may be used during sedated or anesthetized procedures.
The doctor or the veterinary nurse monitoring anesthesia may notice profound bradycardia (slow heart rate) and/or changes in the heart waves on the ECG.
The veterinary team will determine how to respond, based on the severity of the rhythm abnormality, the dog’s condition, and the medications being used.
In severe cases, this finding may prompt reversal of sedation/anesthesia medications and waking the patient up. Dogs with Mobitz Type II heart blocks may be at increased risk during anesthesia and require careful monitoring.
If your dog has ever experienced a heart block before and you now take them to another clinic, be sure to let your current veterinarian know.
Treatment of Heart Block (Mobitz Type II) in Dogs
The treatment of your dog’s heart block depends on the underlying cause.
If a mild first- or second-degree block is noted during anesthesia in a puppy and this resolves after surgery, no treatment may be necessary.
However, if your dog has developed a chronic second-degree AV block following degenerative aging changes, the cardiologist may recommend a pacemaker. A pacemaker works to keep your dog’s heart rate steady and consistent by sending out regular small electrical signals.
To implant this device, the veterinary cardiologist will put your dog under anesthesia and make a small incision in the neck over the jugular vein.
A thin wire, called a lead, is advanced to the heart and secured there. It feeds back to a small device placed under the skin.
This procedure, while it may sound scary, is minimally invasive.
A dog with underlying heart disease that contributed to the heart block may be prescribed heart medications to manage the preexisting condition.
The specific medications will depend on the type and severity of the underlying heart disease.
For example, dogs with certain types of heart disease or congestive heart failure may be prescribed Vetmedin (pimobendan), enalapril, or furosemide.
If your dog developed a heart block secondary to an electrolyte or mineral imbalance due to an underlying disease, it must be managed to treat the heart block. For example, if your dog has Addison’s disease, they may be prescribed prednisone and Percorten-V (desoxycorticosterone pivalate) to manage the Addison’s disease.
Recovery and Management of Heart Block (Mobitz Type II) in Dogs
Frequent rechecks and monitoring are a large part of recovery and management of Mobitz Type II blocks.
A dog who had a transient Mobitz block because of an underlying medical condition may no longer have an issue after their disease is managed.
For example, a dog who had undiagnosed Addison’s disease may have had a second-degree heart block on their ECG when they were in an emergency setting. After they start treatment and their disease is managed, they may no longer have trouble with the electrical conduction in their heart. Alternatively, if your dog has primary heart disease, they may have a Mobitz block long term that requires careful monitoring.
If a second-degree block was diagnosed, your vet will likely recommend repeat ECG testing to ensure it’s not worsening over time.
Additionally, monitoring energy levels at home is helpful to track cardiovascular health. Having an established routine of leash walking your dog can help you notice sooner if they’re developing exercise intolerance and are hesitant to go their normal route or distance.
An activity monitor may help you track changes in your dog’s activity level, but it should not replace veterinary ECG monitoring for a heart block.
Sometimes, special prescription diets are recommended for dogs with underlying heart disease, like Hill’s Prescription Diet h/d Heart Care or Purina Pro Plan Veterinary Diets CC CardioCare.
These diets may be used for conditions such as mitral valve disease (MMVD) or other forms of cardiac disease.
Prevention of Heart Block (Mobitz Type II) in Dogs
Mobitz Type II heart block in dogs can’t always be prevented.
However, regular wellness checks can help your veterinarian detect heart disease and other medical problems that may affect cardiac function.
Regular monitoring of the heart and screening for disease with lab work can help identify medical conditions that may contribute to heart problems.
Manage underlying heart disease and don’t skip out on follow-up monitoring. Medication doses sometimes need to be adjusted.
If your dog is started on a new medication, monitor them closely for any changes in behavior and give all medications exactly as prescribed.
Keep your dog heart-healthy with regular exercise and a well-balanced diet.
Heart Block (Mobitz Type II) in Dogs FAQs
What is the prognosis for Mobitz Type 2 heart block?
The prognosis for dogs with a Mobitz block varies depending on the severity of the block, whether the dog has symptoms, whether the condition progresses, and whether there is underlying heart disease. Dogs with more persistent AV blocks may require a pacemaker.
Can Mobitz Type II heart block in dogs get worse?
Yes. Mobitz Type II can progress to a more severe AV block, so your veterinarian may recommend repeated ECGs or other cardiac monitoring to watch for changes. Dogs who develop symptoms such as weakness, collapse, or fainting should be evaluated promptly.
Does a dog with Mobitz Type II heart block need a pacemaker?
Not always. Treatment depends on the underlying cause, prevalence of the heart block, and whether your dog has symptoms. Dogs with more severe AV blocks, particularly those with symptoms such as fainting, may need a pacemaker to maintain an appropriate heart rate.
Can Mobitz Type II heart block go away?
Sometimes, depending on the cause. If the heart block is associated with a reversible problem, such as anesthesia or a treatable medical condition, it may resolve. Heart blocks caused by disease or degeneration of the heart’s conduction system may be persistent and require ongoing monitoring or treatment.
