Acquired Valvular Heart Disease in Animals

Acquired Valvular Heart Disease

• Acquired valvular heart disease is a common condition in various animal species, including dogs and horses.
• Mitral valve disease is frequently affected by acquired valvular issues. Aortic valve issues are also common in horses.
• In dogs, the condition progresses with age, and prevalence is higher in males (1.5x).
• Cavalier King Charles Spaniels are at a higher risk, along with Dachshunds, Cocker Spaniels, beagles, and various terrier breeds.
• Approximately 30% of dogs with myxomatous mitral valve disease (MMVD) will develop congestive heart failure (CHF).
• Acquired valvular disease is not restricted to canine species; it also affects horses.

Learning Objectives

• Understanding the valves affected by this disease in various species (dogs, horses, and others).
• Knowing the pathophysiology of acquired valvular disease and how it leads to heart failure in different species.
• Proficiency in appropriate diagnostic procedures to detect the disease in dogs and horses.
• Comprehending the different stages of ACVIM Classification for valvular disease in dogs and the appropriate treatment at each stage.
• Recognizing the clinical signs and physical examination findings in cases of acquired valvular heart disease, with or without congestive heart failure (CHF), in various species.
• Understanding the treatment therapies for CHF secondary to acquired valvular disease in animals.

Outline

• Definition of acquired valvular heart disease, including the various types of valve diseases (mitral, aortic).

• Clinical features of acquired valvular heart disease, including symptoms, physical exam findings (murmurs, palpation), and progression in different species.

• Pathophysiology of acquired valvular heart disease, including the disease process leading to heart failure, volume overload, and its effect on the cardiovascular system in different species.

• Physical examination findings (murmurs) of acquired valvular heart disease, specific to dogs and horses.

• Diagnostics for acquired valvular disease, including

  • Echocardiography (finding thickened/irregular valve leaflets, assessing for regurgitation (MR), LA and LV enlargement)
  • Thoracic radiographs (evaluating cardiac silhouette, vertebral heart score (VHS), looking for cardiomegaly in lateral and DV/VD views)
  • Electrocardiography (ECG) (assessing for arrhythmias)
  • Other diagnostics (blood work, blood pressure, NT-proBNP)

• Management/Staging of the disease (following ACVIM classification scheme)

• Understanding the etiology of the disease in various species (Myxomatous valvular heart disease, Degenerative valvular heart disease, Endocardiosis).

  • Etiology, presentation, and clinical courses for the different species.

Normal Valve Structure

• Atrialis: Composed of elastic and collagen fibers
• Spongiosa: Contains an extracellular matrix (ECM) rich in proteoglycans and occasional interstitial cells
• Fibrosa: Tightly packed collagen fibers

Myxomatous Valve

• Non-inflammatory, progressive disarray of valve structure
• Interstitial cells become active
• Excessive deposition of the extracellular matrix (ECM)
• Fragmentation of collagen and elastic fibers
• Damage to the endothelial cell lining, leading to valvular dysfunction.

Dogs (Clinical Features)

• Acquired valvular disease is a frequent cause of heart disease in dogs (>70%) across various breeds.
• Small and medium breeds (<20 kg) are more susceptible.
• Prevalence and severity increase with age.
• More common in male dogs than in female dogs.

Valve Involvement

• Mitral valve alone is a common cause, with or without affecting the tricuspid valve.
• The majority of dogs have mitral valve alone or combined with tricuspid; aortic/pulmonary valves are less frequently affected. In horses, Aortic issues are the most frequently detected.

Normal Mitral Valve

• Separates the left atrium (LA) and left ventricle (LV), functioning as a one-way valve.
• Open during diastole and closed during systole.
• The structure includes:
  • Annulus
  • Leaflets
  • Chordae tendineae
  • Papillary muscles
• Valve leaflets should be thin, translucent, and smooth

Myxomatous Mitral Valve

• The mitral valve structure is disrupted with thickened, nodular leaflets.
• Chordae tendinae are thickened.
• The valve may prolapse or become flail, potentially leading to chordal rupture.

Pathophysiology (Myxomatous Degeneration & Mitral Regurgitation)

• Myxomatous degeneration of mitral valve tissue affects its normal function leading to abnormal motion, and potentially mitral regurgitation.
• Abnormal valve motion leads to mitral regurgitation.
• This abnormal blood flow causes volume overload, increasing LA size (enlargement), and triggering eccentric hypertrophy of the left ventricle (LV).

Pathophysiology (Chronic Decompensated MR)

• Chronic mitral regurgitation (MR) leads to decompensation with increased pulmonary pressure and congestion.
• Right ventricular (RV) function declines, with a subsequent reduction in forward stroke volume.
• Left sided heart failure can potentially arise
• Pulmonary hypertension can also ensue due to these changes.

Physical Exam - Murmur

• Murmur intensity typically increases with disease progression in both dogs and horses.
• PMI is usually localized to the cardiac apex on the left side in dogs. In horses, the murmurs are found at the cardiac base, left of the aorta.
• Murmurs may vary depending on the affected valve, whether they are systolic or diastolic, and their characteristics.

Clinical Signs

• Mild cases may be asymptomatic, but cases often show reduced exercise capacity, colic-like signs, heart rhythm disturbances, and congestive heart failure (CHF), potential leading to sudden cardiac death, in both dogs and horses.

Diagnostics

• Echocardiogram for accurate diagnosis, including evaluation of valve structure, function, and chamber sizes.
• Thoracic radiographs to assess cardiac size and identify possible cardiomegaly in both lateral and DV/VD views.
• Electrocardiogram (ECG) to evaluate for arrhythmias;
• Evaluating for systemic blood pressure & blood work (including NT-proBNP).

Echocardiogram

• Definitive diagnostic in various species, via echocardiogram.
• Shows thickened and irregular leaflets, assessing for regurgitation, and chamber sizes (particularly LA and LV).
• Demonstrates aortic/mitral regurgitations and valve thickening in the different species.

Thoracic Radiographs

• Evaluating cardiac silhouette size, vertebral heart score (VHS).
• Monitoring for progressive disease.
• Assessing the presence of cardiomegaly and distinguish between possible cardiac and respiratory causes of clinical signs

Mitral and Aortic Valve Diseases: Dogs

• Presenting ACVIM classification scheme (asymptomatic, B1, B2, C, D, stages) for staging severity of the disease in dogs.
• Details on clinical features and diagnostic procedures (echocardiogram, ECG, and radiographic findings) are relevant for dogs as well as horses.

ACVIM Classification

• Classifying cases into asymptomatic and symptomatic types (B1, B2, C, D) based on severity.

MMVD with CHF

• Cardiomegaly characterized by left atrial and ventricular enlargement.
• Interstitial to alveolar patterns (typical distribution).
• Pulmonary venous distension.

Electrocardiography (ECG)

• ECG may show normal variations or arrhythmias.
• Secondary to cardiac stretches.
• Examples include atrial, premature complexes, tachycardia, and fibrillation.

Other Diagnoses

• Blood pressure monitoring (not typically elevated in MMVD)
• NTproBNP - Cardiac biomarker, helpful for detecting progressive valve disease and for determining the cause of clinical signs.
• Comprehensive bloodwork (CBC, chemistry, urinalysis (UA), recommended before initiating therapy.
• 24-hour Holter monitors, event recorders – detect arrhythmias outside the hospital.

Other Species

• Acquired valvular disease can affect various species, including cows, parrots, and other animals, with unique considerations relevant for each species.

Horses

• Acquired valvular disease is common in adult horses (>10 years of age), usually male horses.
• Aortic insufficiency is the typical presentation resulting in a diastolic murmur.
• Diagnostic tests (Echocardiography, ECG, 24-hour Holter monitoring, bloodwork) are all important to confirm the diagnosis.
• Clinical outcomes range from asymptomatic cases to severe diseases.