Feline hypertrophic cardiomyopathy, hypertension, and hyperthyroidism (Proceedings)
Feline Restrictive Cardiomyopathy - (RCM)
Restrictive cardiomyopathy is an uncommon myocardial disorder characterized by endomyocardial fibrosis, stiffened ventricular wall and impaired ventricular filling. This is mainly a diastolic disorder. Systolic function may be normal or decreased. Etiology is unknown. Biventricular CHF with pleural effusion and thrombi commonly develop in the markedly dilated atria.
* In many cases, there is significant overlap of clinical signs, ECG and radiographic findings between cats with hypertrophic, dilated and restrictive cardiomyopathy. Echocardiography is needed to complete the diagnosis.Arterial Thromboembolism
Thromboembolism can occur with all forms of feline cardiomyopathy. Three factors are typically required for clot formation. Endomyocardial injury, blood stasis and altered coagulability. Endomyocardial injury is likely due to injury and fibrosis in the large dilated left atria. Exposed collagenous fibers as well as reactive substances that occur with fibrosis act as reactive substances for platelet adhesion and large, dilated atria may have areas of decreased contractility where blood pools. Finally, cats have large, sticky platelets and platelets release serotonin, as well we other factors that lead to a hyperaggregable state. Other coagulation abnormalities may be present in cats with cardiomyopathy
Historically, treatment was directed towards removal or lysis of clot. This is no longer recommended due to high mortality associated with rapid clot removal that is likely a result of reperfusion injury and hyperkalemia among other factors. Now, treatment is directed towards PAIN RELIEF that might include Butorphanol (+/- acepromazine as tranquilizer) and Epidural (requires skill in local anesthesia) or Fentanyl patch (does not provide immediate relief)
The prognosis is frequently poor, but approximately 35-40% regain use of limbs. Although many cats will regain use of motor function within 1-2 weeks, risk of a second episode is high. Many owners elect euthanasia due to the patient's discomfort and concurrent heart disease
The best method for prevention is not known but one could consider a platelet inhibitor such as clopidogrel (Plavix) 18.75 mg/cat q24 hrs (more potent than aspirin, described in JAVMA, 2004;225:106-1411). For cats that have had one episode, many suggest adding a low molecular weight heparin. A less expensive, but likely weaker option would be aspirin (81 mg every 72 hours). There is no clear evidence yet that clopidogrel is any more effective than aspirin although studies are ongoing. Generally, some type of anticoagulant preventative therapy is recommended for all cats with atrial enlargement and any form of cardiomyopathy.