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Congestive Heart Failure and Medical Therapy

Written By:

Nick A. Schroeder, DVM, DACVIM

What is the treatment for congestive heart failure?

The mainstay of medical therapy of congestive heart failure is the careful use of a class of drugs called diuretics. Diuretics cause the kidneys to excrete sodium (salt), which in turn causes water loss through the kidneys, resulting in a reduction of the overall body water and blood volume. This lowers pressure on the veins in the lung tissue and thereby decreases the formation of heart failure fluid (pulmonary edema). Since diuretics affect the kidneys, overzealous use can lead to dehydration and blood salt (electrolyte) imbalances. This may be manifested as lethargy, vomiting and a lack of appetite. Clinicians monitor patients of diuretics with blood tests. The most common diuretic prescribed is a drug known as furosemide (LASIX®, SALIX®). Other diuretics that are commonly used include spironolactone (ALDACTONE®), and hydrochlorothiazide (THIURETIC®, ESEDRIX®, HYDRODIURIL®). Diuretics are the most important medications an animal with acute congestive heart failure receives, and can save the life of a pet in a crisis.

Another group of drugs commonly prescribed to animals suffering from congestive heart failure affect the blood pressure. The most common medications used inhibit an enzyme called angiotensin-converting enzyme (ACE). These include enalapril (ENACARD®) and benazepril (LOTENSIN®). These medications reduce blood pressure and decrease the workload on the failing heart. They also limit the kidneys’ ability to retain salt and water, and temper the effect of certain hormones on the failing heart. Since they also affect the kidneys, blood work is often monitored when pets are on these medications. Other drugs of different types can also be used to treat animals with overtly high blood pressure (hypertension). These medications include amlodipine (NORVASC®) and hydralazine (APRESOLINE®). Regular monitoring of blood pressure is necessary to prevent overdosage.

Phosphodiesterase-inhibitors have been used for over a decade now in the treatment of congestive heart failure. These drugs include pimobendan (VETMEDIN®). This drug acts on the heart muscle to sensitize it to the effects of calcium, which in turn increases the force of the muscle contraction. It also acts on the blood vessels to help them to relax, reducing the workload on the failing heart. Other phosphodiesterase inhibitors that may be used in certain conditions (i.e. pulmonary hypertension) include sildenafil (VIAGRA®, REVATIO®).

Cardiac glycosides (digitalis glycosides) have been used for centuries in medicine to treat congestive heart failure. The most commonly used drug is digoxin (LANOXIN®). This medication can strengthen the contractile force of the heart muscle, making it function better as a pump. Digoxin may also be used to slow the heart rate down, allowing for better filling of the heart chambers. There is a relatively narrow therapeutic range, and animals exhibiting signs of overdose may be inappetent, or have vomiting and diarrhea. If a pet on this medication shows any of these signs, it is wise to stop the medication and inform the veterinarian immediately.

Beta-blocking agents are antiarrhythmic drugs that may be administered to pets with congestive heart failure. Beta-blockers can help slow scarring that occurs with long-standing heart disease. Furthermore, they can help to slow the heart rate, which is frequently high in animals suffering from congestive heart failure. This allows for more effective filling of the heart and can improve heart function. Examples of beta-blockers include propranolol (INDERAL®), atenolol (TENORMIN®), metoprolol (TOPROL®), carvedilol (COREG®) and sotalol (BETAPACE®). Careful monitoring by the veterinarian is necessary to minimize side effects, which can include low blood pressure, collapse and worsening of congestive heart failure.

Calcium-channel blockers are another group of antiarrhythmic drugs that animals with congestive heart failure may be given. These drugs can also be used to slow the heart rate, and are often used in combination with digoxin to effectively treat those patients with fast heart rates that are contributing to or caused by congestive heart failure. The most commonly used drug is known as diltiazem (CARDIZEM®, DILACOR®).

Pets diagnosed with congestive heart failure may ultimately be placed on multiple medications, and careful monitoring by the veterinarian is necessary to minimize adverse effects. Many medications are started at a low dose, and slowly increased depending on how well the animal is tolerating therapy. Since arrhythmias may necessitate specific therapy, additional medications may be required. Some animals with congestive heart failure may also have fluid accumulate in the chest cavity outside the lungs (pleural effusion) or in the abdomen (ascites). Intermittent drainage (thoracocentesis or abdominocentesis, respectively) may be necessary to improve the pet’s ability to breathe. Aspirin or clopridogrel (PLAVIX®) may be prescribed to cats at risk for the development of a thrombus or “clot” within the heart. Dietary manipulation in the form of salt-restricted diets may also improve the quality of life in pets with congestive heart failure. At some point, medical therapy becomes less effective, and despite adjustments in the drugs, animals may become refractory to the medications.