Dilated Cardiomyopathy: Chronic Therapy

By | 2013-06-07

Diuretic Therapy

Diuretics are the only drugs that can routinely control the clinical signs referable to congestion and edema due to heart failure. Consequently, it is mandatory for cats with congestive heart failure to be on a diuretic, usually furosemide. The chronic orally administered dose for furosemide in cats is wide and ranges from 0.5 mg/lb a day to 2 mg/lb every 8 hours. The most common doses are 6.25 to 12.5 mg per cat every 8 to 12 hours, orally. In general, cats need a lower dose of furosemide when compared with dogs, although the upper end of the dose range can be similar. The goal of diuretic therapy is to keep pulmonary edema and pleural effusion controlled. This should be done with the lowest possible furosemide dose, although in the author’s experience, underdosing appears to be a more frequent problem than does overdosing. Every owner should be instructed to count his or her cat’s respiratory rate at home when the cat is sleeping or resting quiedy in a cool environment and to keep a written log. The normal respiratory rate for a cat is in the 20 to 40 breaths per minute range. If the rate is greater than 40 breaths per minute or the owner notes that the character of breathing is more labored, these are signals that an increased dose of furosemide, pleurocentesis, or both are needed. Changes in furosemide dose should be done in consultation with a veterinarian during the initial stages of management. Some owners will require continued contact with a veterinarian to manage dose changes, whereas others will reach a point where they feel comfortable doing this on their own. Cats with severe disease that require a maximum dose of furosemide are often mildly to moderately dehydrated and mildly to moderately azotemic. As long as they continue to eat, drink, and appear comfortable, the dose of furosemide should not be decreased. If the dehydration or azotemia becomes severe enough to cause anorexia, the furosemide administration must be discontinued as long as the cat is not taking in fluid. Owners must be warned that continued use of high-dose furosemide administration in a cat that is not drinking or eating can result in severe, life-threatening dehydration. Judicious use of parenteral fluid administration may be required. These, of course, are poor prognostic signs. Cats that are refractory to the maximum dose of furosemide may need to have another diuretic administered along with the same maximum dose of furosemide. Choices include a thiazide diuretic and possibly spironolactone. () Parenteral administration of furosemide may also be beneficial because the oral bioavailability of the drug is only around 50%.

Pleurocentesis

Repeated pleurocentesis is often required in cats with pleural effusion. Pleurocentesis may need to be done as infrequently as once a month or as frequendy as every 4 or 5 days. As much fluid as possible should be removed at each visit. Ultrasound guidance often helps identify regions where fluid has pocketed. Chylothorax secondary to heart failure can result in chylofibrosis, making it very difficult to remove as much fluid as one would like. Risks of repeated pleurocentesis include infection, pneumothorax, and bleeding, but all are rare.

Angiotensin-Converting Enzyme Inhibitors

Any cat with idiopathic dilated cardiomyopathy should be on an angiotensin-converting enzyme (ACE) inhibitor for long-term management unless they have an adverse reaction to the drug. Enalapril is most commonly used at a dose of 1.25 to 2.5 mg per cat orally every 24 hours. angiotensin-converting enzyme inhibitors can almost never be used on their own to control signs of heart failure and are not effective for controlling heart failure in the acute care setting. Rather they must be administered in concert with a diuretic and help in the long-term control of the disease. Generally, angiotensin-converting enzyme inhibitor therapy should be started when the cat is reasonably stable and not dehydrated.

Digoxin

Digoxin, in theory, may be administered to cats with dilated cardiomyopathy. However, in the initial trial that identified taurine deficiency as a cause of feline dilated cardiomyopathy, digoxin was not administered and most of those cats survived; therefore clearly in cats with dilated cardiomyopathy due to taurine deficiency, no clear mandate exists to administer digoxin.

Dietary Modifications

Any cat with dilated cardiomyopathy should be supplemented with 250 mg taurine orally every 12 hours until the results of the plasma and whole blood taurine concentration analysis are evaluated. Taurine is inexpensive and can be purchased from health food stores or chemical supply houses. Cats that are taurine deficient should be continued on taurine supplementation, whereas those that are not may be taken off or left on at the discretion of the owner. Sodium-restricted diets may be useful, particularly in cats that are refractory to drug therapy. However, it is more important to keep the cat eating than it is to force sodium restriction.