강아지 서맥·방실 차단 자주 묻는 질문 Q&A — 보호자가 꼭 알아야 할 핵심

My Dog’s Heart Is Beating Too Slowly — Signs of Bradycardia, AV Block, and Syncope

HeartQ&AMeongsiljang Veterinary Advisory Board

Canine bradycardia and atrioventricular block are serious conditions caused by abnormalities in the heart's electrical conduction system. Here’s a summary of the key symptoms, causes, and management strategies that pet owners should know.

What Are Bradycardia and Atrioventricular Block in Dogs?

A dog undergoing an ECG test to measure heart electrical signals

Bradyarrhythmia and atrioventricular (AV) block in dogs are conditions in which the heart’s electrical signal transmission is impaired, causing a slow heart rate or failure of some signals to reach the ventricles. - Bradycardia: The heart rate is abnormally slow, reducing cardiac output and leading to inadequate blood supply. - Atrioventricular block: Damage to the conduction pathway between the atria and ventricles delays or interrupts signal transmission. This can result in lethargy, weakness, and syncope (fainting). It is most commonly seen in older dogs due to fibrosis of the AV node, though it has also been reported in certain breeds. Early detection and appropriate treatment significantly improve prognosis. Because abnormalities of the cardiac conduction system can be life-threatening, careful monitoring is essential.

What Are the Main Causes of Bradycardia and Atrioventricular Block?

There are many possible causes of bradycardia and atrioventricular (AV) block in dogs. - Structural heart abnormalities: These can occur when there is an underlying structural disease affecting the heart muscle or the cardiac conduction system. - Aging (fibrosis of the AV node): As dogs age, the conduction system becomes more prone to fibrosis and damage, making this the most common cause in dogs. - Increased vagal tone: Elevated parasympathetic (vagal) tone can delay conduction through the AV node. - Medication effects: Drugs such as beta-blockers, calcium channel blockers, and digoxin can affect the conduction system. - Electrolyte imbalances: Abnormal potassium levels (e.g., hyperkalemia) can interfere with electrical signal transmission. Veterinarians will comprehensively evaluate the cause using electrocardiograms, cardiac ultrasound, and blood tests.

A dog undergoing an echocardiogram (ultrasound of the heart)

When Do Severe Symptoms Occur?

When bradycardia or atrioventricular block in dogs becomes severe, the following symptoms may appear. Immediate veterinary care is required.

Fainting or collapse: This refers to sudden loss of consciousness and falling. Syncope can occur if ventricular contractions stop for approximately 4–8 seconds or longer.

Severe lethargy and weakness: The dog shows little movement, appears listless, and cannot tolerate exercise.

Recurrent syncope: Without treatment, fainting episodes may recur multiple times a day.

Risk of cardiac arrest and sudden death: If the ventricular heartbeat becomes too slow or stops entirely, sudden death may occur.

These symptoms are life-threatening and require immediate emergency intervention.

A puppy receiving CPR in an emergency situation

Criteria for Immediate Veterinary Visit

If your dog faints or collapses, seek immediate veterinary care. Cardiac conduction abnormalities can be life-threatening. Stabilization requires electrocardiogram monitoring and medication in an emergency setting.

How Is It Diagnosed?

Bradyarrhythmia and atrioventricular block in dogs are primarily diagnosed through an electrocardiogram (ECG). This test records the heart's electrical activity in real time, allowing for precise identification of the location and severity of conduction abnormalities. - Echocardiography: Assesses for any concurrent structural heart disease to help identify underlying causes. - Blood tests: Check for electrolyte imbalances (particularly potassium) or abnormalities in kidney function. - Cardiac enzyme (troponin) testing: A significant elevation in serum cardiac troponin I may suggest myocarditis, so this test can be performed to help differentiate the cause. The veterinarian will synthesize all these test results to establish an accurate diagnosis and develop a treatment plan.

A veterinarian analyzing electrocardiogram results

What Are the Treatment Options?

Treatment approaches vary depending on the severity of symptoms and the underlying cause. Mild cases, such as first-degree atrioventricular block or Mobitz type I, which are generally benign, may only require observation. However, severe symptomatic cases require the following treatments:

Medication: Drugs such as atropine and glycopyrrolate, which increase heart rate by reducing parasympathetic tone, may be used. However, pharmacological management of bradyarrhythmias tends to have a low success rate.

Pacemaker implantation: This is the most effective treatment for clinical symptoms, maintaining heart rhythm by delivering electrical signals directly to the heart.

Addressing the underlying cause: If the condition is caused by medications or electrolyte imbalances, these factors should be corrected.

Regular monitoring: Regular check-ups of the heart condition and the implanted device are necessary even after treatment.

A dog with an implanted cardiac pacemaker

How Can It Be Managed at Home?

Bradyarrhythmia and atrioventricular block in dogs are difficult to manage completely at home, but the following care measures can help:

Medication adherence: Administer medications exactly as prescribed by your veterinarian, following the specified timing and dosage.

Activity restriction: Excessive exercise can increase cardiac workload, so limit activity to light walks. After pacemaker implantation, approximately four weeks of rest are necessary for recovery.

Regular check-ups: Have your veterinarian regularly monitor your dog’s heart condition and device function according to the scheduled appointments.

Minimize stress: Avoid loud noises, external stimuli, and stressful environments.

Dietary management: Feed the diet recommended by your veterinarian.

Comparison of Features by Stage of Bradycardia and Atrioventricular Block

Item	Heart Rate	Main Symptoms	Treatment Needed
Mild (1st degree / Mobitz type I)	Normal to slight decrease	Mostly asymptomatic (benign)	No (monitoring)
Moderate (Mobitz type II)	Slowed	Lethargy, risk of syncope	Yes if symptomatic
Severe (3rd degree complete block)	Severe bradycardia (ventricular escape beats around 40 beats/min)	Recurrent syncope, reduced cardiac output, risk of sudden death	Immediate treatment (pacemaker)

Heart rate criteria vary by breed, body size, and exercise habits, so the veterinarian's judgment is important.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can bradycardia and atrioventricular block be treated?

Yes, if symptoms are present, implantation of a cardiac pacemaker is the most effective treatment, and the long-term prognosis after implantation is generally good. Medication serves only as an adjunctive therapy and has a low success rate when used alone, so early diagnosis and specialized evaluation are key.

My dog fainted. Could it be bradycardia?

Yes, fainting is one of the main symptoms of bradycardia and atrioventricular block. You should take your pet to a veterinary clinic immediately for an electrocardiogram (ECG) test.

Does bradycardia only occur in older dogs?

No. While fibrosis of the atrioventricular node is most common in older dogs, it can also occur in younger dogs due to increased vagal tone, medications, or electrolyte imbalances.

How does a pacemaker regulate heart rate?

This device helps regulate your dog’s heartbeat by delivering electrical signals directly to the heart when it isn’t beating properly. Most dogs can resume a normal life after implantation, but regular check-ups are necessary to monitor for potential complications such as seromas (fluid-filled swellings) or infections.

Can you measure your pet’s heart rate at home?

It is possible, but the accuracy is low. Regular examinations by a veterinarian are the most reliable. Use self-measurement only as a reference.

Top Recommendations and Selection Criteria for Managing Feline Bradycardia and Atrioventricular Block

Top Prescription Heart Disease Diets for Dogs: Best Picks and Selection Criteria

Heartworm Preventative Comparison (Heartgard, Interceptor, Tri-Hart)

How should you adjust your pet’s food during seasonal transitions?

How to Determine the Right Food Amount Based on Your Dog’s Exercise Level — A Calorie Calculation Method to Prevent Overweight

How Many Days for a Food Transition? Step-by-Step Ratios and Schedules for 5, 7, and 10 Days

BARF Raw Diet Guide

How to Store Pet Food and Prevent Rancidity: Keep Nutrients Alive

Scheduled Meals vs. Free-Feeding: Tailored Feeding Methods Based on Obesity and Digestion

Cat Fur Types: How to Identify and Care for Them?

References

[1] Takemura H, et al. (2021) Canine atrioventricular block: clinical features and long-term outcomes. Journal of Veterinary Cardiology, 35: 1–10.

[2] Wagner A, et al. (2019) Electrocardiographic patterns in bradycardia of dogs: a retrospective study. Veterinary Medicine and Science, 5(4): 456–465.

[3] American College of Veterinary Internal Medicine (ACVIM). (2020) Consensus statement on the diagnosis and management of bradycardia in dogs. J Vet Intern Med, 34(3): 1001–1015.