Atrioventricular (Complete) Heart Block in Dogs: 2025 Vet Guide 🩺🐾

By Dr. Duncan Houston BVSc

Welcome—I'm Dr Duncan Houston, BVSc, veterinarian and founder of Ask A Vet. This in-depth 2025 guide covers canine complete (third-degree) AV block: what it is, diagnostic steps, treatment options including pacemaker implantation, prognosis, breed risk, home care, telemedicine, and future directions.

1. 🐾 What is Complete AV Block?

Complete AV block (third-degree) happens when electrical signals from the atria (via SA node) can't pass through the AV node. As a result, the atria and ventricles beat independently, with a slow ventricular escape rhythm.

2. 🧬 Underlying Causes

• Congenital defects: Some dogs are born with AV node abnormalities.
• Idiopathic fibrosis: degenerative scarring of the conduction system—a common cause.
• Myocarditis/endocarditis: an inflammatory disease damaging AV conduction.
• Infiltrative disease: amyloidosis, neoplasia.
• Electrolyte imbalances: hyperkalemia (e.g., from Addison’s) can lead to reversible block.
• Drug toxicity: digitalis, etc..
• Ischemia: MI affecting conduction.
• Age-related degeneration: Older dogs tend to develop it.

3. 🐕 Breed & Risk Factors

• Cocker Spaniels, Pugs, Dobermans: predisposed breeds.
• Older dogs: AV node fibrosis increases with age.
• Dogs with myocarditis, Addison’s, Lyme, Chagas, neoplasia, or on cardiac meds.
• Cavalier King Charles Spaniels: cases reported, but not a primary risk.

4. ⚠️ Recognizing Symptoms

Signs include:

• Marked bradycardia (<40–60 bpm).
• Weakness, exercise intolerance, fainting, or collapse.
• Coughing, difficulty breathing due to low cardiac output.
• Cranial “cannon A waves” and jugular pulsations in some dogs.
• Some asymptomatic dogs, incidentally found on ECG.

5. 🧪 Diagnostic Pathway

1. History & Physical: Check pulse, heart sounds, and respiratory signs.
2. ECG: Confirms AV dissociation—P waves at sinus rate, QRS at slower escape rhythm.
3. Holter monitoring: Useful for intermittent or asymptomatic cases.
4. Bloodwork: CBC/chemistry to detect inflammation, infection, or electrolyte issues.
5. Echo & X-rays: Evaluate heart structure, myocarditis, chamber size.
6. Atropine challenge: Helps differentiate vagal vs intrinsic AV block.
7. Special tests: Infectious serology, endocrine testing if Addison’s suspected (hyperkalemia).

6. 🛠 Treatment & Management

6.1 Immediate Medical Support

• Stabilize with oxygen, IV fluids.
• Treat reversible causes—e.g., normalize electrolytes in Addison’s cases.
• Temporary pacing (transcutaneous or transvenous) if bradycardia causes syncope or hypotension.
• Atropine, theophylline, terbutaline may offer short-term heart rate support.

6.2 Permanent Pacemaker—Standard of Care

Pacemaker implantation is recommended for symptomatic dogs or those at risk of sudden death.

• Types: Single or dual-chamber, transvenous or epicardial.
• Cavalier case: Dual-chamber epicardial pacemaker resolved AV dissociation and improved heart function.
• Success rates: 90% clinical improvement; median survival post-implant ~26 mo (range up to 70 mo), 41% still alive at study end.
• Long-term survival: Another study reported median survival ~856 days (3 years) across 13 dogs.

6.3 Post-Implant Care

• Monitor for infection, lead displacement.
• Regular check‑ups: ECG, thoracic X-rays, pacemaker telemetry every 6–12 months.
• Medications: manage CHF or underlying disease.
• Exercise: moderate, gradually resumed; no vigorous activity until stable.
• Emergency plan: know the warning signs of device failure or infection.

7. 📈 Prognosis & Life Expectancy

• Without a pacemaker, the prognosis is poor, risk of sudden death.
• With a pacemaker, many dogs enjoy 2+ years, some even beyond 5 years post-implant.
• Underlying disease (e.g., myocarditis) influences outcome.
• Cats have a better prognosis with AV block & pacemaker, but the risk remains for dogs.

8. 🏡 Home Monitoring & Owner Care

• Daily pulse and respiratory checks.
• Observe energy, appetite, fainting, and coughing.
• Maintain medications for CHF or concurrent conditions.
• Avoid extreme exertion; engage in gentle exercise.
• Ensure scheduled pacemaker check-ups.
• Emergency vet access if symptoms return.
• Track alerts and updates via Ask A Vet’s telehealth app.

9. 🔬 Advancements & Future Trends

• Biological pacemakers: Gene therapy approaches (AAV1-HCN4) show promise in canine models.
• Miniaturized devices: Next-gen pacemakers are smaller, longer-lasting.
• Remote monitoring: Telemetry and wearables feed directly to vets via apps.
• Imaging innovation: AI-based ECG detects early conduction issues before full block.
• Telehealth clinics: Collaboration between Ask A Vet and specialty centers enhances care access.

10. 💬 FAQs from Pet Parents

Is pacemaker surgery risky? 

Minimal risk in experienced hands; complications are rare and manageable.

Can the device fail? 

Battery or lead issues may occur; remote monitoring notifies early, enabling replacement before failure.

Do dogs need meds post-implant? 

Yes—CHF management or treatment for underlying conditions continues.

Will activity restrictions be long-term? 

Low-intensity exercise is generally allowed; avoid strenuous activities.

Is a pacemaker inherited?

No—the need for a pacemaker is due to disease, not directly inherited; however, some underlying conditions may be genetic.

11. ❤️ How Ask A Vet Enhances Care

With Ask A Vet, you get:

• Remote ECG and telemetry review.
• Medication reminders and side-effect tracking.
• Scheduling and interpreting pacemaker check-ups.
• 24/7 access for symptoms like syncope or bradycardia.
• Connection with nearby cardiology centers for implants.

Our app supports owners in caring for dogs with pacemakers or arrhythmias—keeping heartbeats safe and steady!

12. 🔚 Summary

Complete AV block is serious but treatable. Recognizing slow heart rate, collapse, or weakness is vital. Diagnosis relies on ECG and evaluation to identify reversible causes. Treatment centers on pacemaker implantation, which restores quality of life and extends survival dramatically, often into years. With modern remote monitoring, miniaturized devices, and integrated telehealth, dogs with third-degree AV block in 2025 can thrive under expert and compassionate care.

— Dr Duncan Houston, BVSc