Veterinary CPD webinar – Understanding Heart Murmurs and Congestive Heart Failure in Dogs

What Is a Heart Murmur?

A heart murmur is simply turbulence in the blood flow, which changes the sound of the heart. Murmurs can result from several causes, including:

• Increased blood velocity (e.g. hyperthyroid cats or rapid heart rates)
• Increased blood volume (e.g. fluid overload)
• Reduced blood viscosity (e.g. anaemia)
• Valve regurgitation (leaky valves, the most common cause in dogs)

Murmurs are classified by timing, systolic, diastolic, or continuous and by location, intensity, and grade (1–6), which indicates loudness and the presence of a palpable thrill.

Evaluating Heart Murmurs

When a murmur is detected, Dr Boatright recommends considering:

• Age: Soft murmurs in young puppies are often innocent, while loud or continuous murmurs may indicate congenital disease.
• Breed: Small breeds (e.g. Cavalier King Charles Spaniels) are predisposed to mitral valve disease, while large breeds may develop dilated cardiomyopathy (DCM).
• Clinical signs: Exercise intolerance, coughing, lethargy, weight loss, or respiratory changes increase concern for heart disease.

Diagnostic Approach

To confirm and stage heart disease, Dr Boatright suggests:

• Echocardiography: The gold standard for evaluating valve function and heart structure.
• Chest radiographs: Assess heart size and signs of pulmonary oedema.
• Bloodwork: Check for anaemia, thyroid disease, and overall organ function.
• Electrocardiography (ECG): Identify arrhythmias or electrical abnormalities.
• Blood pressure measurement: Establish a baseline for monitoring.

Monitoring at Home

Owners can help by tracking:

• Resting respiratory rate: Less than 30 breaths per minute is ideal; trends upward may signal worsening CHF.
• Exercise tolerance and appetite: Decreases can indicate advancing disease.
• Weight changes: Loss of body condition may require intervention.

Congenital vs. Acquired Heart Disease

Common congenital murmurs, though rare in practice, include:

• Patent ductus arteriosus (PDA): Continuous murmur; can lead to left-sided CHF.
• Pulmonic stenosis and subaortic stenosis: Systolic murmurs; may cause right- or left-sided heart failure depending on severity.

The most common acquired heart disease in dogs is myxomatous mitral valve disease (MMVD), especially in small breeds. MMVD progresses slowly, and treatment depends on the stage of the disease:

• Stage A: High-risk breeds with no murmur; monitor only.
• Stage B1: Asymptomatic with a murmur, no structural changes; monitor.
• Stage B2: Asymptomatic with structural heart changes; may benefit from early treatment such as pimobendan.
• Stage C: Current or past CHF; requires chronic management.
• Stage D: Refractory CHF; requires specialist-level care.

Chronic Management of CHF

For dogs with MMVD progressing to CHF, treatment typically includes:

• Furosemide: Loop diuretic to reduce fluid overload.
• Pimobendan: Improves heart contractility and provides mild vasodilation.
• ACE inhibitors: Support blood pressure and heart function.
• Spironolactone: Aldosterone antagonist to aid in long-term management.
• Diet: Maintain body condition, limit sodium, and consider omega-3 supplements.

Monitoring involves regular bloodwork, radiographs, ECGs, and blood pressure checks to adjust therapy as needed. Owners must be prepared for long-term management and follow-up.

Arrhythmias in Heart Disease

Atrial fibrillation is common in dogs with cardiomegaly secondary to MMVD or DCM. Treatment focuses on controlling ventricular rate, often with diltiazem or digoxin.

Key Takeaways for General Practitioners

• Heart murmurs are common but not always indicative of disease.
• Breed, age, and clinical signs guide initial concern and diagnostics.
• Echocardiography remains the gold standard for definitive diagnosis.
• Staging heart disease is critical for determining appropriate treatment and monitoring.
• Chronic management of CHF involves a combination of medications, diet, and close monitoring.

Dr Boatright’s practical approach emphasises early detection, careful monitoring, and client communication, allowing general practitioners to manage canine heart disease effectively and improve patient outcomes.