Cardiovascular (CV) diseases in cats include congenital malformations, acquired heart, and vascular disorders. Myocardial
disorders or cardiomyopathies, the major cause of heart failure, thromboembolism, and persistent arrhythmias in cats, constitute
the focus of this presentation. The clinical signs, diagnostic evaluation, complications, and management strategies pertinent
to these disorders overlap considerably. Accordingly, an overview of feline heart muscle diseases is presented followed by
general recommendations for diagnostic testing. Next, some of the unique features of specific myocardial diseases are addressed.
Finally, specific therapeutic approaches are presented for the syndromes of acute and chronic congestive heart failure; the
prevention and management of arterial thromboembolism; and the control of heart rhythm disturbances.
Overview of feline CV diseases
Genetic and idiopathic myocardial diseases are often termed 'primary' cardiomyopathies. These include hypertrophic, dilated,
restrictive, right ventricular, and unclassified cardiomyopathies, as well as myocarditis. Myocardial infarction is a poorly
characterized disorder in cats that causes regional or global ventricular dysfunction. Of these conditions, hypertrophic cardiomyopathy
(HCM) is most common.
Secondary myocardial diseases develop from defined disorders such as systemic hypertension, hyperthyroidism, taurine deficiency,
and growth hormone excess (acromegaly). Echocardiographic findings do overlap between primary and secondary myocardial disorders,
however, these conditions should be distinguished as patient management and long-term prognoses can differ.
Other causes of feline heart disease must be considered in the differential diagnosis of feline cardiomyopathies. Congenital
malformations of the heart and great vessels are observed regularly in cats. Mitral valve malformation, ventricular septal
defects, and atrial septal defects are encountered most often, but other lesions, including peritoneopericardial diaphragmatic
hernia and patent ductus arteriosus must be considered. Although cardiac malformations usually are considered problems of
kittens and young cats, these defects may go unrecognized until maturity.
Moderate to severe anemia is an under-recognized reason for cardiac enlargement. Cats with diabetes mellitus may exhibit myocardial
heart disease, in some cases related to growth hormone excess. Additionally, severe respiratory diseases in cats can induce
pulmonary hypertension and cor pulmonale, sometimes resulting in marked enlargement of the right heart. In contrast to other
species, both degenerative valvular disease and infective endocarditis are very rare in cats. Pericardial effusions in cats
are generally caused by congestive heart failure (CHF) and often resolve with effective treatment of the underlying condition.
Moderate to severe anemia is an under-recognized reason for cardiac enlargement. Cats with diabetes mellitus may myocardial
heart disease, in some cases related to growth hormone excess.
Cardiac rhythm disturbances requiring treatment seem less common in cats when compared to dogs. However, atrial and ventricular
ectopic rhythms do develop in association with cardiomyopathies, cardiomegaly, myocardial fibrosis, myocarditis, ischemia,
infarction, increased sympathetic activity, electrolyte disturbances, hyperthyroidism, and cardiac or systemic neoplasia.
Some persistent rhythm disturbances, including atrial fibrillation, can be idiopathic in cats. Atrioventricular blocks are
observed most often in older cats.
In terms of vascular disorders, idiopathic aortic dilatation, systemic hypertension, and arterial thromboembolism (ATE) are
common diseases of mature cats. Idiopathic aortic dilatation (aortoannular ectasia) is a seemingly benign disorder often observed
in middle-aged and older cats. Whether or not aortic stiffness is altered in this disease, or whether this vascular change
contributes to systolic hypertension, has not been studied. This lesion is frequently associated with subaortic septal hypertrophy
and a systolic murmur, clinical findings that can create confusion about the underlying cardiac diagnosis. Systemic hypertension
is a common cause of LV hypertrophy as well as cardiac murmurs in cats; it rarely advances to CHF or aortic rupture. When
blood pressure (BP) is severely elevated, retinal detachments and hemorrhages, renal injury, CNS depression, and hemorrhagic
stroke are more common outcomes.