Veterinary CPD webinar – Practical Canine Cardiology for New-Graduate Vets in Small-Animal Practice

Common Congenital Cardiac Diseases in Dogs

Patent Ductus Arteriosus (PDA)

Key concept: Persistent connection between the aorta and pulmonary artery → usually a left-to-right shunt.

Signalment

• More common in females
• Hereditary in several breeds

Typical findings in practice

• Continuous “machinery” murmur
• Bounding femoral pulses
• ± exercise intolerance or cough

Reverse PDA clue:
Differential cyanosis (hindlimbs cyanotic, forelimbs pink).

Diagnosis

• Echocardiography (usually via referral)
• Thoracic radiographs: pulmonary overcirculation, enlarged pulmonary arteries

Management

• Left-to-right PDA → referral for occluder/coil (preferred) or surgical ligation
• Reverse PDA → do not close; medical management and monitoring

Shape

Pulmonic Stenosis (PS)

Key concept: Congenital obstruction at the pulmonary valve.

Why you’ll see it often: popular brachycephalic breeds (e.g., French Bulldogs).

Clinical features

• Left basilar systolic murmur ± thrill
• Exercise intolerance, syncope
• Severe cases → sudden death risk

Diagnosis: Echo to grade severity (usually referral)

Management

• Balloon valvuloplasty for moderate–severe disease
• Atenolol commonly used to reduce arrhythmia risk
• Valve will not be normal post-procedure—goal is symptom reduction

Tetralogy of Fallot (TOF)

Four components

• Ventricular septal defect
• Pulmonic stenosis
• Overriding aorta
• Right ventricular hypertrophy

Clinical clues

• Cyanosis (worse with exercise/stress)
• Exercise intolerance, weakness
• Variable murmur

Management

• Often medical
• Control secondary polycythaemia (phlebotomy or hydroxycarbamide)

Subaortic Stenosis (SAS)

Key concept: Fibrous ridge below the aortic valve → LV outflow obstruction.

Signalment

• Large-breed dogs (e.g., Golden Retrievers)
• Hereditary

Important clinical point:
Unlike pulmonic stenosis, SAS can worsen as the dog matures.

Findings

• Left basilar systolic murmur radiating to carotids
• Weak femoral pulses (severe)
• Syncope or sudden death

Management

• Primarily medical (β-blockers)
• Interventional options limited benefit long-term
• Endocarditis risk → peri-operative antibiotics where indicated

ECG Basics for New-Graduate Vets

Lead Placement Memory Aid

• Lead I → left arm–right arm
• Lead II → right arm–left leg
• Lead III → left arm–left leg

AV Block Recognition

• 1st degree: prolonged PR
• 2nd degree Mobitz I: progressive PR ↑ → dropped beat
• 2nd degree Mobitz II: sudden dropped beat
• 3rd degree: complete AV dissociation

Clinical relevance: Mobitz II and 3rd-degree blocks are more concerning.

Premature Beats

• APCs: early P wave, narrow QRS
• VPCs: wide/bizarre QRS
  • Upright in Lead II → right ventricular origin
  • Negative in Lead II → left ventricular origin

Ventricular Tachycardia vs Fibrillation

• VT: rapid wide complexes
• VF: chaotic baseline
• Both shockable if pulseless

Practice tip: very regular “chaos” across leads → suspect movement artefact.

Degenerative Mitral Valve Disease (MMVD)

Most common acquired cardiac disease in dogs.

Key facts

• Degenerative, not congenital
• Cavaliers over-represented
• Not all dogs progress to CHF

Staging (ACVIM)

• A: at-risk breed
• B1: murmur, no enlargement
• B2: enlargement present
• C: CHF
• D: refractory CHF

Treatment highlights

• Pimobendan → start at B2
• CHF → furosemide + pimobendan ± ACEi/spironolactone
• Mitral repair surgery available at some UK referral centres

Dilated Cardiomyopathy (DCM)

Signalment: large breeds (Dobermann, Great Dane).

Causes

• Primary (genetic)
• Secondary (diet-associated, myocarditis)

Echo finding: dilated LV with poor systolic function.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

Classic breed: Boxer
Hallmark: ventricular arrhythmias ± systolic dysfunction

Diagnosis: Holter often more sensitive than echo
Management: sotalol ± other antiarrhythmics

Owners should understand: medication reduces but does not eliminate sudden death risk.

Pulmonary & Systemic Hypertension

Pulmonary hypertension causes

• Chronic lung disease
• Left-sided heart disease
• Heartworm (travel/import history relevant in UK)

Systemic hypertension

• Usually secondary to systemic disease
• Can cause cardiac remodelling

Practical CHF Approach in First-Opinion Practice

Typical presentation

• Tachypnoea
• Left apical systolic murmur
• Crackles

Radiographic clues

• Left atrial enlargement
• Pulmonary venous congestion
• Interstitial/alveolar oedema

Treatment priorities

• Oxygen
• Furosemide
• Pimobendan
• Add ACEi/spironolactone later

When finances are limited

• In-practice oxygen + injectable furosemide
• Send home furosemide + pimobendan
• Recheck within 24–48 h and again at ~1–2 weeks

Pericardial Effusion

Classic triad

• Muffled heart sounds
• Jugular distension
• Weak pulses

Common cause: neoplasia (esp. right atrial haemangiosarcoma).

Critical management principle

• Do NOT give furosemide
• Stabilise with pericardiocentesis

Prognosis depends on underlying cause.

Key Take-Home Points for New-Graduate Vets

• Continuous murmur + bounding pulses → think PDA
• SAS can worsen with growth; PS usually static
• Cyanosis + polycythaemia → consider TOF
• Mobitz II/3rd-degree AV block clinically significant
• Start pimobendan once MMVD reaches B2
• CHF: furosemide + pimobendan first
• Pericardial effusion ≠ diuretic case