Atrioventricular (Mobitz I) Heart 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 detailed 2025 guide, we explore second-degree AV block – Mobitz type I in dogs, known as the Wenckebach phenomenon: what it is, why it usually isn’t harmful, when it warrants attention, how to diagnose and monitor it, and how modern telehealth integrates into long-term care.

1. 🫀 What is Mobitz I AV Block?

Mobitz I is a form of second‑degree AV block where the PR interval progressively lengthens with each beat until a P-wave fails to conduct (a “dropped” QRS), after which the cycle resets.

It typically stems from increased AV nodal refractoriness, often linked to high vagal tone, certain drugs, low calcium, or transient systemic illness.

2. 🧠 Why It’s Usually Benign

Mobitz I is commonly seen in healthy, young dogs, especially during sleep, anesthesia, or high vagal tone states. Most dogs remain asymptomatic, and the condition often resolves spontaneously or remains stable.

3. 👀 Causes & Risk Factors

• High vagal tone (GI, ocular, respiratory stimulation, anesthesia)
• Medication effects—digoxin, bethanechol, pilocarpine, calcium-channel or beta-blockers
• Electrolyte imbalances—hypocalcemia
• Occasionally associated with structural heart disease, neoplasia, or age-associated nodal fibrosis

4. 🧪 How It’s Diagnosed

1. Physical exam & history: rule out meds, vagal triggers, systemic disease
2. ECG: progressive PR prolongation before a dropped beat confirms Mobitz I
3. Blood panels: check electrolytes, calcium, thyroid, and digoxin levels
4. Echo/X-ray: to exclude structural heart disease when suspected
5. Holter monitoring: helpful when block is intermittent or parasympathomimetic effects are suspected
6. Atropine test: rapid PR normalization suggests vagal origin

5. ✅ Treatment & Management

• No treatment required for asymptomatic dogs without underlying disease
• Address underlying causes: correct calcium, adjust medications, treat systemic illness
• Monitor progression: ECG/Holter every 6–12 months or with new signs

6. 🏥 When to Be Concerned

If Mobitz I AV block occurs with:

• Syncope, exercise intolerance, or lethargy
• Underlying structural heart disease, conduction system scarring, or drug toxicity
• Progression to Mobitz II, high‑grade block, or third‑degree AV block

In these cases, further diagnostics and interventions—including atropine response, Holter, or temporary pacing—may be needed.

7. 📈 Prognosis

• Excellent in isolated Mobitz I: most dogs remain asymptomatic and stable long-term
• Potential progression is rare; more likely in dogs with nodal fibrosis or systemic illness
• Symptomatic cases or progression may require intervention, but this is uncommon

8. 🧠 2025 Tools & Telehealth Support

• Wearable ECG patches linked to your phone—monitor rhythm at home
• AI‑powered ECG review via Ask A Vet for early detection of change
• Holter streaming integrated with app for remote specialist review
• Teleconsults to discuss ECG tracings, symptoms, or medication management
• Medication & ECG reminders for consistent follow-up

9. 🏡 Home Care & Lifestyle Notes

• Maintain normal activity unless symptoms emerge
• Track heart rate, breathing, appetite, and energy levels daily
• Avoid AV-nodal suppressants unless directed by your vet
• Use wearable monitors for alerts on rhythm change
• Ensure scheduled checkups (ECG/Holter) via Ask A Vet

10. 🐾 Breed & Age Notes

• Mobitz I is often seen in young, athletic dogs under vagal stress
• Older dogs—Cocker Spaniels, Dachshunds—can develop it due to nodal fibrosis
• Dogs on medications that slow AV conduction require monitoring with ECG or wearables

11. 💬 FAQs

Will this progress? 

Rarely—most cases remain benign unless drugs or structural disease are involved.

Do I need a pacemaker?

No. Pacemakers are reserved for high-grade or symptomatic blocks. 

Should I worry under anesthesia? 

Not usually, but vets may give atropine pre-anesthesia to safeguard rhythm. 

How often should I check my ECG? 

Every 6–12 months, sooner if symptoms start or medications change.

12. ❤️ Ask A Vet Telehealth Benefits

With Ask A Vet, you can:

• Upload ECG or Holter data for expert review
• Receive smart alerts for symmetry or rhythm changes
• Schedule video consults to discuss results and care plans
• Track medications, follow-up dates, and symptom logs

Download our app for smart rhythm monitoring and reassurance throughout your dog’s care journey.

13. 🔚 Final Thoughts

Mobitz I AV block is typically mild and well-tolerated in dogs. Diagnosis is straightforward with an ECG, and management focuses on monitoring and addressing causes. With modern wearables, AI analysis, and telehealth support, owners in 2025 can ensure their dog’s heart stays healthy and stable for years to come.

— Dr Duncan Houston, BVSc