Veterinary Guide to Canine Tetralogy of Fallot 2025: Diagnosis, Treatment & Management 🐾❤️

By Dr. Duncan Houston BVSc

Overview

Tetralogy of Fallot (TOF) is a rare congenital cardiac disorder in dogs, characterized by four structural heart defects: a ventricular septal defect (VSD), pulmonic stenosis, an overriding aorta, and right ventricular hypertrophy. These abnormalities create a right-to-left shunt, leading to low oxygenation and clinical signs like cyanosis, exercise intolerance, and weakness.

📊 Etiology & Breed Predisposition

• Genetic & developmental: Abnormal conotruncal septum formation in utero.
• Breed predisposition: Keeshonds, English Bulldogs, Wirehaired Fox Terriers, and less commonly Labradors and mixed breeds.
• Incidence: Estimated 1 in 4,000 dogs—likely underreported due to early mortality.

🔍 Clinical Signs to Watch For

• Cyanosis (blue gums or tongue), especially during exertion.
• Exercise intolerance, weakness, collapse.
• Stunted growth or failure to thrive in puppies.
• Heart murmur on auscultation—reflects turbulent flow.
• Polycythemia from chronic hypoxia—thick blood volume.
• “Tet spells”—acute episodes of worsened cyanosis and fainting may occur.

📋 Diagnostic Approach

1. Physical Exam & Blood Work

Identify murmur, cyanosis, and polycythemia. CBC often shows elevated hematocrit.

2. Thoracic X-rays

“Boot-shaped” heart due to RV hypertrophy, reduced pulmonary vascular markings.

3. Electrocardiogram (ECG)

Right axis deviation, possible arrhythmias.

4. Echocardiography: The Gold Standard

Echo reveals:

• VSD location and size
• Overriding aorta
• Severity of pulmonary stenosis
• Right ventricular hypertrophy and shunting via Doppler.

5. Advanced Imaging

CT or MRI used selectively to assess anatomy or plan complex surgery.

💊 Management Strategies

Medical Management

• Beta-blockers: Propranolol reduces dynamic obstruction and symptoms.
• Phlebotomy: To control severe polycythemia and related symptoms.
• Supportive care: Oxygen therapy, sedation to reduce stress during tet spells, and periodic monitoring.

Surgical & Interventional Options

• Palliative procedures: Modified Blalock–Taussig shunt to increase pulmonary blood flow—limited veterinary application but reported success.
• Balloon valvuloplasty: To relieve pulmonic stenosis in select cases.
• Open-heart repair: VSD closure and RV outflow tract reconstruction. Rare in veterinary medicine, high complexity, but possible.

📈 Prognosis & Long-Term Management

• Without intervention, most dogs do not survive past 1 year.
• Dogs with mild defects managed medically can live longer, though growth and stamina remain limited.
• Surgically repaired dogs have improved survival and quality of life—data limited to case studies.

🏠 Home Care & Quality of Life

• Strict exercise restriction—avoid overexertion.
• Manage stress and avoid overheating to reduce tet spells.
• Regular check-ups with CBC, echo, and oxygen saturation tests.
• Phlebotomy schedule if polycythemia persists.

💡 Why 2025 Is Different

• Advanced echo techniques (3D imaging, Doppler) enhance diagnostics and surgical planning.
• Minimally invasive interventions—ballooning and shunts—are emerging in specialty centers.
• Telehealth care via Ask A Vet allows remote monitoring, emergency advice during cyanotic episodes.
• Improved anesthetic protocols make procedures safer for cyanotic patients.

🔧 Role of Ask A Vet

• Ask A Vet: Offers 24/7 guidance during cyanosis or collapse, assists in monitoring, medication adjustments, phlebotomy timing.

👨⚕️ Final Thoughts from Dr Duncan

Tetralogy of Fallot in dogs is a serious congenital heart defect—but with prompt diagnosis, tailored medical intervention, and advanced imaging, many affected pups can live comfortable, managed lives. Ongoing follow-up, home monitoring, and specialty referral are essential for optimal care in 2025. 💙

Visit AskAVet.com or download the Ask A Vet app for expert telehealth support—from diagnosing cyanosis to guiding phlebotomy and beyond.