ECG remains key diagnosticfor cardiomyopathy in cats - DVM
  • SEARCH:
News Center
DVM Featuring Information from:

ADVERTISEMENT

ECG remains key diagnosticfor cardiomyopathy in cats


DVM360 MAGAZINE


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 technology.

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.


ADVERTISEMENT


Click here