Many atrial and ventricular arrhythmias can occur with cardiomyopathy. The most common ventricular arrhythmia is premature
ventricular complexes. A paroxysmal or sustained ventricular tachycardia is rarely seen. Supraventricular arrhythmias do occur,
but are not common. Atrial fibrillation will be seen and must be considered to be associated with a poor prognosis. Atrial
fibrillation usually only develops with massive left atrial enlargement. This tachycardia further compromises ventricular
filling and also seems to be associated with a higher risk for thromboembolic disease.
ECG primary diagnosticEchocardiography is the primary diagnostic procedure for diagnosing cardiomyopathy in cats. Echocardiography detects the presence
of early or advanced heart failure by detecting the presence of atrial enlargement. It also allows differentiation of the
various forms of cardiomyopathy through assessment of ventricular dimensions as well as contractility.
The 2-D echocardiographic views can also document the presence of left ventricular outflow tract obstruction. Advanced cardiac
hypertrophy is easy to document on echocardiography. Septal or left ventricular free wall measurements of greater than 5 mm
in diastole are consistent with left ventricular hypertrophy. With hypertrophic cardiomyopathy, reduction of the size of the
left ventricular lumen will be seen. Contractility will be normal or increased in most instances.
The differentials for these findings include primary hypertrophic cardiomyopathy and hypertension, and hyperthyroid heart
disease. When hypertrophy is detected on an echocardiogram, a blood profile that includes thyroid testing is indicated. Since
hypertension is almost always secondary to either hyperthyroidism or chronic renal failure in cats, the blood work will be
able to identify risk factors for hypertension. Ideally, blood pressure should be measured using either Doppler or oscillometric
Echocardiography also allows the diagnosis of hypertrophic obstructive cardiomyopathy as well as systolic anterior motion
of the mitral valve. Left atrial enlargement is indicative of beginning pulmonary congestion and may be a precursor to heart
failure. In addition, thrombi can occasionally be seen in the left atrium. Occasionally, a swirling effect termed "smoke"
can be seen in the left atrium. This is thought to be a sign of pooling of blood in the left atrium and may also be a marker
of impending thromboembolism.
Dilated cardiomyopathy is also relatively easy to diagnose by echocardiography. Dilated cardiomyopathy tends to involve both
the right and left ventricle. Both ventricles tend to be dilated with very poor contractility and thinning of the ventricular
walls. Biatrial enlargement and pleural effusion are commonly found and sometimes pericardial effusion.
Restrictive and intermediate cardiomyopathyThe more difficult echocardiographic diagnoses to make are restrictive and intermediate cardiomyopathy. These tend to have
a combination of findings that are not consistent with the diagnosis of hypertrophic cardiomyopathy or dilated cardiomyopathy
but are associated with significant atrial enlargement.
The wall thicknesses of the left ventricle are often near normal or only mildly thickened. The ventricular lumen tends to
be mildly dilated. Contractility tends to be in the normal range. In restrictive cardiomyopathy, contractility can be quite
reduced and the endomyocardium can be quite bright on echocardiography. It is quite possible that these forms of cardiomyopathy
represent a spectrum of changes so that they often do have features of both dilated and hypertrophic cardiomyopathy.
TreatmentTreatment should attempt to control the signs of clinical heart disease as well as prolong the lifespan of the cat. It is
uncertain whether any of the treatments currently available definitely prolongs the cat's lifespan.
It is also uncertain whether asymptomatic animals benefit from early intervention with cardiac medications. Controlling the
signs of heart disease does tend to be possible with a wide variety of medications. Treatment for cardiomyopathy varies depending
on the type of cardiac muscle disease present, at least in regard to maintenance therapies.
The treatment for acute heart failure tends to be independent of the form of cardiomyopathy present. The cats with acute heart
failure tend to present in severe respiratory distress and can easily decompensate. Initial management focuses on managing
the dyspnea. The dyspnea can be from pleural effusion, pulmonary edema or a combination of these two.
Minimizing stress in these cats is vital and often too much intervention by the veterinarian early on can have a negative
effect on the cat's condition. Initially placing the cat in an oxygen cage is recommended to allow them to calm down from
the trip to the veterinary office as well as to improve oxygenation. An oxygen cage also has the advantage of muffling upsetting
noises found in most veterinary practices. If significant pleural effusion is present, thoracocentesis should be considered.
Since these cats tend to be in very poor condition, it often is possible to perform this without sedation or local anesthesia.
Start meds immediatelyMedications should be started immediately on initial presentation. Furosemide (2-4 mg/kg intramuscularly or intravenously)
can be administered; although the benefits of intravenous administration (more rapid onset of action) must be weighed against
the risk associated with the restraint necessary to place an intravenous catheter. Nitroglycerine ointment (2%) can also be
administered and is appropriate for emergency care. In most cats one-fourth inch of ointment is applied to an area with minimal
hair (inside of an ear or inner thigh) every six to eight hours. After 48 hours, it is thought that animals become refractory
to the effects of the nitroglycerine ointment.
Nitroglycerine ointment should not contact bare skin of people. It will be absorbed and a glove should be worn when applying
nitroglycerine ointment. Nitroglycerine ointment also has the advantage of having some antithrombotic effects that can be
helpful in cats with cardiomyopathy.
In cats it can at times be difficult to tell the difference between an animal suffering from acute heart failure and one suffering
from an acute asthma attack. In those cases where the two cannot be differentiated and in which it is considered too risky
to the animal to take immediate thoracic radiographs, furosemide, nitroglycerine and medications for asthma should be administered.
Asthma treatment with injectable aminophylline (4 mg/kg intramuscularly) is usually adequate. Corticosteroids such as dexamethasone
(0.25 to 1 mg/kg intramuscularly) are also commonly used to treat asthma but this could be deleterious to the heart in cats.
The cat is placed in a cage (preferably with supplemental oxygen) to rest. After the cat has stabilized, it is then possible
to perform diagnostic procedures (thoracic radiographs, ECG, echocardiogram) as needed to establish a definitive diagnosis.
Chronic therapy is directed at controlling signs of heart failure and ideally to slowing down progression of the disease.
Therapy for heart failure is relatively the same, independent of the form of cardiomyopathy present. The therapies directed
at slowing progression can vary between the various forms of cardiomyopathy.
Diuretics are needed to control the signs of pulmonary congestion that occur with cardiomyopathy. The most commonly used diuretic
is furosemide (1-2 mg/kg once to twice daily). For, most cats a furosemide dose of 2 mg/kg twice daily should not be exceeded.
Dehydration can easily occur. In addition, furosemide may lead to potassium depletion, so electrolyte and kidney values should
be checked routinely.
In those cases where furosemide alone without or with addition of an ACE inhibitor cannot control pulmonary congestion, addition
of a second diuretic should be considered, such as spironolactone or spironolactone/chlorothiazide combinations. The diuretic
dose is usually 1-2 mg/kg once or twice daily. These diuretics are potassium sparing and are probably not as potent as furosemide.
Diuretics are titrated to effect, that is until signs of congestive heart failure are controlled.
ACE inhibitorsACE inhibitors have an important function in the treatment of heart failure. Their use in dilated, restrictive and intermediate
cardiomyopathy is usually not contraindicated. In hypertrophic cardiomyopathy, there are theoretical drawbacks for use of
ACE inhibitors. ACE inhibitors are arterial and venous dilators. With the arterial dilation, pressure downstream from the
heart should be reduced. In hypertrophic cardiomyopathy, especially if hypertrophic obstructive cardiomyopathy is present,
this effect could worsen the prolapse of the mitral valve (less pressure downstream counteracting the tendency of the mitral
valve to move into the outflow tract). ACE inhibitors do have a positive influence in cats with hypertrophic cardiomyopathy
and refractory heart failure. The dosage is 0.25 to 0.5 mg/kg of enalapril or benazepril daily. Renal function should be monitored
when these medications are used - generally check BUN, serum creatinine and serum potassium values three to five days after
starting an ACE inhibitor and again 10-14 days later to make sure that azotemia does not occur.