Dilated Cardiomyopathy

a.k.a. Congestive Cardiomyopathy

• Common in dogs

• Rare in cats (with adequate taurine supplementation)

Signalment

Dog: Giant and Large Breeds (e.g. Dobermann pinscher, Boxer, Great Dane); Male>Female; Risk increases with age

Cat: Greatest risk in: Siamese, Burmese, Abyssinian; Male>Female; Middle Age & Old Age

Description

• Dilated cardiomyopathy (DCM) occurs when there is a progressive reduction in systolic myocardial contractility. Decreased myocardial contractility affects the removal of blood from the ventricle at systole. A larger volume of blood increases the end diastolic pressures causing dilation of the ventricle and the development of eccentric hypertrophy.

Diagnosis

History & Clinical Signs

-Asymptomatic (Occult) DCM: See in predisposed breeds (e.g. Doberman pinschers)

-Right-Sided Congestive Heart Failure Signs

• Giant Breeds usually prone to these

-Left-Sided Congestive Heart Failure Signs

• Boxers and Doberman pinschers have a higher risk

-Syncope

-Weight Loss

-Dyspnoea

-Lethargy

-Weakness

-Hindlimb Paresis (cats with saddle thrombi)

Physical Exam

-Systolic Murmur

-Gallop Rhythm

-S3 Heart Sound (+/-)

-Arrhythmias

-Pulse Deficits

-Pulmonary crackles

Laboratory Findings

-Azotemia

-Elevated Liver Enzymes (+ Liver Congestion)

-Signs of congestive heart failure

-Signs of thromboembolism (cats)

-Plasma taurine reduction (cats)

Radiography

-Left Ventricular Hypertrophy (Seen in Dobermans & Boxers)

-Left Atrial Enlargement (Seen in Dobermans & Boxers)

-Generalized Cardiomegaly (Seen in Giant Breeds)

-Left-Sided Congestive Heart Failure signs (pulmonary congestion & edema)

-Right-Sided Congestive Heart Failure signs (pleural effusion, ascites)

Electrocardiography (ECG)

-Rhythm Disturbances (e.g. Atrial fibrillation (Giant Breeds); Ventricular Arrhythmias (Doberman pinchers, Boxers))

-Conduction Disturbances

-Characteristic signs of hypertrophy

Echocardiography

-Hypokinetic left ventricle (i.e. reduced fractional shortening therefore reduced contractility)

-Reduced ejection fraction (i.e. % end diastolic volume ejected at systole)

-Decreased ventricular wall thickness

-Left atrial enlargement

-Mitral regurgitation

Treatment

-Treat congestive heart failure (Reduce Preload & Afterload; Improve Systolic Function; Control Cardiac Arrhythmias)

-Therapeutic thoracocentesis (To remove pleural effusion) (cats)

-Taurine Supplementation (cats)

Prognosis

Dogs

-Poor: Most breeds survive 6-12 months

-Grave: Dobermans and Boxers

Cats

-Good: When cardiomyopathy results from taurine deficiency

-Grave: Other causes of cardiomyopathy

From Pathology

Incidence:

Most common form in the dog. Seen in young to middle aged dogs of large breeds:

• St Bernard
• Great Dane

Clinical signs:

Disease is a slowly progressive dilation of the ventricles with a loss of contractility. This is seen histologically as random myofibrillar thinning and degeneration of myocyte mitochonria, although it is possible that no histological lesions are present.

Clinical signs will appear as a sudden onset disease as there will be an acute decompensation for the pathology that had accumulated gradually. Signs include those of a congestive heart failure:

• Pulmonary oedema.
• Ascites.
• Hepatomegaly and splenomegaly.

Diagnosis:

Gross cardiomegaly with cardiac hypertrophy, dilation and decreased contractility. Histopathologically; increased attenuated wavy fibres within the myocardium. Fibres are thinner than normal and have a wavy appearance. May develop due to a chronic volume overload.

• Ventricular dilation, particularly the left ventricle, distorts the AV-valves which often become incompetant.
• Fibrillation is a common finding as dilation of the myocardium induces abnormal electrical activity and arrhythmias.

Variations of the disease exist in specific breeds:

• Doberman: Present with arrhythmias. Histologically there are lymphocytic infiltrates within the ventricular myocardium. See focal degeneration of the bundle of His, probably due to narrowing of small vessels near the conductive tissue.
• English Cockers: Familial with many dogs having sub-clinical disease.

View images courtesy of Cornell Veterinary Medicine

Secondary to toxic agents

Includes:

• Dilated myopathy in horses with monensin toxicity.
• Dilated myopathy in dogs with long term administration of doxorubicin.
• Dilated myopathy in cats due to taurine deficiency.

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