Lecture 13: Canine Myocardial Diseases

What is the difference between primary and secondary cardiomyopathy?

 Primary (intrinsic) cardiomyopathy:

• Myocardial disease primarily affecting heart

• Genetic mutation is frequently cause

• Also includes certain non-genetic or acquired

Secondary (extrinsic) cardiomyopathy:

• Myocardial disease secondary to another identifiable systemic (multiorgan) disease

• Endocrine, amyloid, glycogen, etc

• Ischemic cardiomyopathy

• Doxorubicin cardiomyopathy

• Diet-Associated DCM

What are the clinical manifestations of cardiomyopathy?

• Congestive heart failure: Dyspnea, Exercise intolerance

• Cardiac arrhythmias: Syncope, episodic weakness

• Thromboembolism: Acute lameness, other signs, Dyspnea

• Sudden Death

What is a primary myocardial disease characterized by ventricular dilation and systolic dysfunction (usually most prominent left ventricle)?

DCM

What are the clinical consequences of DCM?

• Heart failure

• Arrhythmias

• Sudden death

Who is predisposed to DCM?

• Large & giant breed middle-age to older dogs - Males over-represented

• Genetic: Doberman & Boxer

• Nutritional: Taurine deficiency, carnitine deficiency & grain-free diets

What is the typical presenting history of DCM?

• Variable cough, dyspnea (worse at night), syncope, weakness, collapse, anorexia, exercise intolerance, weight loss

• Sometimes misdiagnosed with “bronchitis” in last 3 weeks

What is the typical presenting physical exam of DCM?

• Muffled or soft heart sounds

• Soft systolic murmur (mitral or tricuspid)

• Gallop or irregular rhythm, +/- tachycardia

• Weak pulses, pulse deficits

• Jugular distension, ascites or crackles (CHF)

What pathology is associated with DCM?

• Fibrosis

• Inflammation

• Lipid accumulation

• Myocyte degeneration

• Edema

• Variable by breed and case

What diagnostics are demonstrative of DCM?

ECG:

• A fib, VPCs, ventricular arrhythmias, APCs

• LA &/or LV enlargement patterns

• Conduction disturbances

Thoracic radiographs:

• Cardiomegaly (esp. L side)

• Pulmonary edema (L CHF)

• Pleural effusion or ascites (R CHF)

Biomarkers:

• ↑ NT-proBNP, ↑ cTnI (supportive)

• Genetic testing (Doberman, Boxer, Schnauzers)

What is seen on an echocardiogram of DCM?

• Dilated ventricles, thin walls

• Decreased systolic function

• Reduced ejection fraction (< 45-50%)

• Secondary mitral +/- tricuspid regurgitation

• Left atrial enlargement

What diets are associated with DCM?

• Association between certain diets and DCM

• Diets high in peas, pea fractions, lentils, chickpeas, +/- sweet potatoes, potatoes or other uncommon sources

• Many of these diets advertised as Grain Free diets

What breed are predisposed to taurine deficiencies and therefore predisposed to DCM associated w/ taurine deficiency?

• Golden Retrievers

• Cocker Spaniels

• Newfoundlands

What breed are predisposed to carnitine deficiencies and therefore predisposed to DCM associated w/ carnitine deficiency?

• Boxers

• Cocker Spaniels

• Dobermans

What are the key diagnostics and information of DCM cases?

• echocardiogram and ECG

• thoracic rads

• CBC, chem, UA, NT-proBNP

• HW status

• blood taurine concentration

• blood pressure

• cardiac troponin I

• diet history

What drugs are used for DCM chronic management?

What is the treatment for DCM?

What is the prognosis for DCM?

What is seen in doberman pinscher cardiomyopathy?

• Occult cardiomyopathy

• Ventricular arrhythmias

• Between 45-63% of Dobermans have DCM

• 40 to 50% with DCM may die suddenly

• Ventricular arrhythmias/ventricular fibrillation

• Cardiogenic shock

• Specific genetic tests

What is seen in boxer cardiomyopathy?

What is seen in DCM of giant breed dogs?

• Left heart failure or biventricular failure

• Atrial fibrillation is common

• Sudden death is possible

• Survival shorter if CHF

• Asymptomatic with arrhythmia alone - often a prolonged survival (Lone atrial fibrillation?)

What is seen in cardiomyopathy of irish wolfhounds?

• Left atrial enlargement & arrhythmias are hallmarks

• Chylous pleural effusion sometimes develops if overt DCM

• Up to 50% of “normal” dogs have a CV abnormality

• Fractional shortening is higher than many dogs with cardiomyopathy

• Atrial fibrillation is common and may be first sign of cardiomyopathy

• Disease can be slowly progressive

• Some dogs with presumed “Lone Atrial fibrillation” progress to DCM

What is seen in english and american cocker spaniel cardiomyopathy?

• Average age 6-10 years (range 10 mo-13 years)

• Nearly equal male : female ratio

• ECG - LVE pattern with tall R wave, APC’s common

• Generalized cardiomegaly with pulmonary edema

• Many have low plasma or whole blood taurine concentrations

• Taurine and carnitine supplementation can result in clinical and echo improvement in some dogs

• Pimobendan may slow progression of disease

What is seen in DCM of newfoundlands?

• Typically, middle age or older

• Some “normal” dogs have fractional shortening between 20-28%

• Atrial fibrillation is common

• Sudden death less common than other breeds?

• Taurine deficiency if eating certain diets (high fiber, lamb and rice, etc)

• Refractory CHF is the most common cause of death/euthanasia

What is seen in juvenile DCM in portuguese water dogs?

• Sudden death and peracute CHF

• 5 weeks to 3-4 months of age

• Necropsy / echo findings = typical DCM

• Conflicting reports about the role of taurine

• Genetic mutation – Chromosome 8

• Arrhythmias infrequent, soft murmur or gallop

• Pulmonary edema, hepatomegaly

• Some with normal echo at 6 weeks of age developed DCM before 6 mo of age

What does doxirubricin (adriamycin) toxicity cause?

• DCM-like syndrome

• Oxidant injury

• Arrhythmias

• Lower dose problematic in dogs predisposed to DCM

• Cats less sensitive

• If cardiomyopathy develops, often poor response to Rx

What effect does canine hypertrophic cardiomyopathy have?

• Very uncommon

• German Shorthaired Pointers +/- German Shepherds, Shi Tzu

• Genetic basis in German Shorthaired Pointer (?)

• Conduction abnormalities, 3rd degree AV block, ventricular arrhythmias

• CHF may develop

• Sudden death first sign in some cases

What are the common possible features of myocarditis?

Common possible features:

• CHF

• Arrhythmias

• Thromboembolic disease

Often the heart is a bystander; other organ systems dominate the clinical picture

What is trypanosomiasis - Chagas disease?

Trypanosoma cruzi from Reduviidae bug – vector (kissing bug) in Texas, Mexico, South and Central America → Severe myocarditis, Right atrium and ventricle may predominate, Left-sided or Right-sided CHF

What is the treatment for Chagas disease?

• Treatment with Ragonil (benznidazole), but this might not improve cardiac outcomes

• Manage cardiac dysfunction and arrhythmias with Rxs