Category:Cardiomyopathy

Degenerative-Cardiomyopathy

The majority of cardiomyopahies in domestic species are idiopathic in aetiology. There are three forms if idiopathic cardiomyopathy:

• Dilated
• Hypertrophic
• Restrictive

Dilated cardiomyopathy

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

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (cat). Courtesy of T. Scase

Incidence:

The cat is most commonly affected. There is some evidence of inheritance, as in man, and the disease is said to be more common in male cats. There is a wide age range of 7 months to 24 years.

Inherited in Maine Coon cats.

Clinical signs:

Grossly there is disproportionate hypertrophy of the left ventricle and often the interventricular septum. The chamber size is dramatically reduced.

Histologically there is haphazard hypertrophy of the myocardial fibres.

The reduction in left ventricular volume and the stiffened ventricular wall results in diastolic dysfunction, the stroke volume is reduced resulting in congestive heart failure and the following clinical signs:

Hypertrophic cardiomyopathy (cat). Courtesy of T. Scase

• Tachycardia.
• Arrhythmia (abnormal myocardium)
• Dyspnoea.

The force of the left ventricular contraction reduces afterload and reduces end-systolic volume to zero in some cases. This is cavity obliteration.

• Thromboembolic disease is a frequent complication. The thromboemboli most often impact in the femoral arteries manifesting as an acute hindlimb paralysis.

Restrictive Cardiomyopathy

Other Cardiomyopathies

Feline Hyperthyroidism

A hypertrophic cardiomyopathy is seen secondary to this disease in elderly cats. Thyroid hormones induce the growth of the myocardium.

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.