Atrioventricular (First‑Degree) Block in Dogs: 2025 Vet Guide 🩺🐶

By Dr. Duncan Houston BVSc

Hello, I’m Dr Duncan Houston, BVSc, veterinarian and founder of Ask A Vet. In this informative 2025 guide, we explore first-degree atrioventricular (AV) block in dogs—what it is, why it happens, when it matters, how it's diagnosed, and how to monitor it using modern telehealth strategies.

1. 🩺 What Is First‑Degree AV Block?

First‑degree AV block is a mild conduction delay: electrical impulses pass normally from the atria to the ventricles, but the PR interval is prolonged (>130 ms) on ECG. There’s no dropped beat, only slowed signal transmission.

2. ✅ Why It Often Doesn’t Cause Symptoms

This condition rarely produces clinical signs. It may appear in:

• Young, healthy dogs with high vagal tone, particularly during stress or anesthesia.
• Older dogs, especially Cocker Spaniels and Dachshunds, due to age-related conduction system degeneration.

3. ⚠️ Possible Underlying Causes

While often benign, first‑degree AV block can indicate other conditions:

• High vagal tone from GI, ocular, respiratory, or sedation sources.
• Drug effects—digoxin, bethanechol, pilocarpine, calcium-channel blockers, beta blockers.
• Electrolyte imbalances, especially calcium deficiency.
• Structural heart issues—degenerative disease, cardiomyopathy, myocarditis, infiltrative disease, conduction system fibrosis.

4. 🧪 Diagnostic Approach in 2025

1. History & Physical: Attention to medications, breed risks, and vagal-tone triggers.
2. ECG: Assess PR interval, confirm prolonged conduction without dropped beats.
3. Bloodwork: Screen for calcium, electrolytes, thyroid, and organ function.
4. Imaging: Echo to evaluate cardiac structure; chest X-ray as needed.
5. Holter Monitor: Recommended if intermittent higher-grade block is suspected.

Atropine testing can help determine if high vagal tone is the main issue.

5. 🩺 When Is Treatment Needed?

Treatment depends on symptoms and cause:

• No treatment for silent, idiopathic, or vagal-tone cases. Periodic monitoring is advised.
• Drug-induced block—discontinue or adjust offending medication.
• Electrolyte imbalance—correct deficiencies like hypocalcemia.
• Structural heart disease—treat underlying issue, monitor for block progression.

6. 📆 Monitoring & Prognosis

• Recheck ECG and physical exam every 6–12 months.
• Repeat ECG after medication changes or onset of symptoms such as lethargy, collapse, or exercise intolerance.
• Echo frequency guided by breed risk and underlying structural findings.
• Simple cases typically remain stable without progression.

7. 🏥 Role of Telehealth in 2025

With the Ask A Vet app, you can:

• Upload ECG tracings or Holter data for remote cardiologist review.
• Get reminders for ECG check-ins and follow-up appointments.
• Receive alerts if your dog’s heart rate slows or symptoms emerge.
• Schedule video consults to interpret rhythms and adjust care plans.

8. 🐶 Breed and Age Considerations

• Young, athletic dogs often experience vagal-tone block, benign.
• Cocker Spaniels and Dachshunds: age-related degenerative causes.
• Dogs on AV node–impacting drugs or with existing heart disease require extra vigilance.

9. 🧠 2025 Innovations & Emerging Tools

• Wearable ECG monitors—for home rhythm tracking.
• AI-powered ECG interpretation—detect subtle PR prolongations.
• Remote Holter devices—data streamed to vet via Ask A Vet.
• Medication management—integrated into telehealth platforms.

10. 🤔 FAQs for Pet Parents

Will first‑degree block worsen? 

Rarely—most stay stable unless another cause arises. 

Do I need a pacemaker? 

No—pacemakers are reserved for higher-grade blocks with syncope. 

Can meds cause this? 

Yes—especially AV node‑affecting drugs. Your vet may adjust doses.

Is it dangerous before anesthesia? 

Usually benign, but vets may give atropine pre‑anesthesia as a precaution.

11. ❤️ How to Ask A Vet Helps

Using Ask A Vet, you can:

• Submit ECGs for cardiologist interpretation
• Schedule teleconsults after detection of PR prolongation
• Receive alerts if progression toward a higher-grade block occurs
• Track medication schedules and any changes to heart‑healthy regimens

Download our app to seamlessly support your dog’s cardiac health, adding expert rhythm monitoring to routine care. 🐾

12. 🔚 Final Summary

First‑degree AV block in dogs is usually benign, requiring only observation unless caused by drugs, electrolyte imbalance, or structural disease. With advanced ECG tools, AI‑powered analysis, wearables, and telehealth support, owners in 2025 can monitor their dog’s heart rhythm at home, detect changes early, and collaborate closely with their vet. While pacemakers are not needed for this mild block, regular check‑ups and rhythm tracking help maintain heart health and peace of mind.

— Dr Duncan Houston, BVSc