Hypertrophic Cardiomyopathy

• Rare in dogs

• Common in cats

Hypertrophic cardiomyopathy (cat). Courtesy of T. Scase

Hypertrophic cardiomyopathy (cat). Courtesy of T. Scase

Signalment

Dogs: Rare

Cats: Pedigrees (e.g. Persians, Maine Coons) & mixed breeds; Occurs in young pedigrees and young to old mixed breeds; Male>Female

Description

• Left ventricular concentric hypertrophy without an identifiable cause is known as hypertrophic cardiomyopathy. The ventricular myocardium becomes so thick that the lumen is reduced to a size that is not compatible with maintaining the heart's function as a pump. The left ventricle no longer has the capacity to hold normal volumes of blood during diastole. As a result, the left atrium dilates from the increased pressure and volume of blood backing up into the lungs.

Diagnosis

History & Clinical Signs

-Asymptomatic

-Hindlimb paresis or weakness (saddle thrombus see in cats)

-Signs of left-sided heart failure

Physical Exam:

-Systolic murmur

-Ventricular arrhythmias

Radiography

-Left atrial enlargement

-Enlarged heart

-Pulmonary congestion & edema

Electrocardiography (ECG)=

-Tall R wave

-Wide QRS

-Ventricular arrhythmias

-Conduction disturbances

-Sinus tachycardia

Echocardiography

-Left ventricular concentric hypertrophy

-Left atrial enlargement

-Mitral valve insufficiency

Treatment

-Treat the individual symptoms

Contraindications: Arterial Vasodilators; Positive Inotrops

Prognosis

-Poor for symptomatic cats

From Pathology

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.

Feline Hyperthyroidism

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