Treating heart failure (Proceedings)

Chronic heart failure (CHF) traditional therapy (for CHF secondary to chronic degenerative valvular disease etc.) still provides only an average a 4-6 months survival time in dogs. Though current standard treatment regimens provide a good quality of life for many canine patients, complications can lead to early patient loss. Ongoing congestion or syncope can be concerns, sudden death due to arrhythmias, or client-elected euthanasia due to poor quality of life may also lead to loss.

Combination therapy is essential and must be customized to each patient. Different stages of heart failure, and differences in types of failure depending on breed, etiology, and concurrent illness make it necessary to fine tune therapy both on a per-patient basis, and within the patient, to adjust therapy based on response or non-response during the treatment timeline.

Mild to Moderate Heart Failure

Clinical signs of heart failure are evident at rest or with mild exercise and adversely affect the quality of life. Typical signs of heart failure include exercise intolerance, cough, an increased respiratory rate, dyspnea, and mild to moderate ascites. Home treatment is often indicated at this stage. For mitral valvular endocardiosis patients, diuretic therapy, ACE inhibitor therapy, and sodium-restricted diets are indicated. Digitalis therapy would also be indicated, especially if the ECG shows any atrial arrhythmias. For the dilated form of cardiomyopathy, treatment recommendations would include digitalis (especially with atrial fibrillation), pimobendan, diuretic therapy, ACE inhibitors, antiarrhythmic drugs for atrial and/or ventricular arrhythmias, sodium restriction, possible indications for carnitine and/or taurine supplementation (especially for Cocker Spaniels) and, on some occasion, beta-blockers.

Advanced Heart Failure

Clinical signs of advanced congestive heart failure are immediately obvious. These clinical signs could include respiratory distress (dyspnea), marked ascites, profound exercise intolerance, or hypoperfusion at rest. In most cases, hospitalization is mandatory. Treatment for advanced heart failure includes: oxygen therapy, aggressive diuretic therapy, topical nitroglycerin, ACE inhibitors, pimobendan, digitalis (especially if atrial arrhythmias are present) and, in very severe cases, dobutamine or sodium nitroprusside. If ascites is refractive to therapy, combining spironolactone with furosemide can sometimes be effective. The fluid will also have to be periodically tapped. Antiarrhythmic drug therapy is also sometimes indicated to control the heart rate in atrial fibrillation and will often include digoxin, diltiazem, and also a beta-blocker.

It is important in all cardiac failure cases to monitor renal status, electrolytes, hydration, respiratory rate, heart rate and body weight. If azotemia develops, reduce the dosage of the diuretic. If azotemia persists and the animal is also on an ACE inhibitor, reduce or discontinue the ACE inhibitor. Use digoxin with caution if azotemia develops.

To prevent cardiac failure, it is important to restrict exercise and sodium intake in patients with heart disease. Recent studies are now showing that prescribing an ACE inhibitor early in the course of heart disease in patients with dilated cardiomyopathy may slow the progression of heart disease and delay the onset of heart failure. ACE inhibitors should be considered in asymptomatic animals if they have dilated cardiomyopathy. Studies are still pending on the use of ACE inhibitors for preventative care.

Benazepril

Benazepril is an angiotensin converting enzyme inhibitor (ACEI), licensed in Canada in dogs (0.25 mg/kg SID) and in Europe for use in cats greater than 2.5 kg (0.5-1.0- mg/kg SID); indications are for chronic renal insufficiency (CRI), and in dogs for congestive heart failure (CHF). This drug shows great promise as an adjunctive therapy because there is also new evidence to suggest that this drug may play a role in treatment of hypertrophic cardiomyopathy in cats, though this is currently an off-label use.

In cats with CRI, in vivo effects include increased blood flow in the kidneys, with efferent arteriolar vasodilation, variable GFR, reduced protein loss in the urine, significantly increased appetite and weight gain, prolonged survival, mild reduction in blood pressure, reduced risk of hypokalemia, and improved quality of life. The extent of proteinuria in CRI cats has been shown to be a predictor of rate of progression of CRI, and so U-protein levels may potentially serve a screening function, and reducing proteinuria may slow progression of CRI.

The usual benazepril dose for cats for CRI is 0.5-1.0 mg/kg once daily PO and dosage adjustment in mild to moderate renal insufficiency is not necessary since 85% of metabolites are excreted through biliary pathways, and only 15% via the kidneys.

Pimobendan: What You Need to Know

This drug is a:

• Positive inotrope, [inodilator]-- a benzimidazole pyridazinone derivative

• Drug used as an adjunct with other CHF drugs

• (in combination with furosemide and benazepril, for example)

• Calcium sensitizer [ at Ca++ binding sites of troponin C]—leads to improved systolic efficiency without leading to significantly increased myocardial oxygen requirement and intracellular calcium buildup

• Mixed arterio- and veno-dilator

The Use of Carvedilol in Heart Failure in Dogs

The primary action of this drug is a beta blocker. Chronic beta receptor blockage helps to prevent the progression of congestive heart failure disease. Heart pathology in the early phases is associated with chronic sympathetic nervous system activation.

This was the first beta blocker licensed in people for treatment of congestive heart failure. Studies in people with advanced heart failure prove carvedilol benefits patients by lowering risk of death, lowered the risk of advancing heart failure, and reduced the incidence of ventricular tachyarrhythmias. This drug is now just being adopted in dogs with heart failure secondary to idiopathic dilated cardiomyopathy or less commonly, chronic degenerative valvular disease. A 12 hour dosing interval provided protection in healthy dogs subjected to experimentally (isoproterenol) produced tachycardia.

Significant antiarrhythmia action can takes place (80% reduction in ventricular ectopy—measured with Holter 24 hour monitoring). This effect was seen in Boxer and Doberman Pinscher dogs with dilated cardiomyopathy. Unfortunately, controlled clinical trials are still not available in heart failure dogs, and experience with this drug still not widespread.

Treatment of Feline Cardiomyopathy

Thoracocentesis should be performed in all dyspneic cats when pleural effusion is suspected. Give furosemide when pulmonary edema is present. In the crisis setting, give 2-4 mg/kg IV initially, then 1-2 mg/kg IV or IM every 4-6 hours until the edema has resolved. Furosemide is often continued as needed (6.25-12.5 mg SID-BID) to control edema formation. Apply 1/4 inch of nitroglycerin to a hairless area every 4-6 hours until the edema has resolved. Administer via face mask if tolerated; otherwise use an oxygen cage or tent (50% oxygen).

Diltiazem may improve myocardial relaxation and control arrhythmias. Give 7.5 mg TID or 30 mg of a sustained-release preparation SID-BID. Alternatively to diltiazem, a beta-blocker, such as atenolol (6.25 mg SID-BID) may be used. The use of benazepril: 0.25 mg/kg SID may be beneficial. ACE inhibitors have been shown to possibly reduce left ventricular hypertrophy in cats. Aspirin may reduce chance of thrombus formation; give 81 mg every third day. Cats with persistent tachycardia may benefit more from a beta-blocker than a calcium channel blocker. Monitor renal function if enalapril is used.

References

Tilley, L.P., and Smith, F.W.K. (Eds): The Five Minute Veterinary Consult-Canine & Feline Medicine 4th Edition. Ames, Iowa, Wiley Blackwell Publishing, 2008.

Tilley, L.P., Smith, F.W.K., Oyama, M., and Sleeper, M.: Manual of Canine & Feline Cardiology, 4th Edition.Elsevier, St. Louis, 2008.

Kittleson, M.D., Kienle, R.D.: Small Animal Cardiovascular Medicine. Philadelphia, Mosby, 1998.