heartfailuretherapy

Heart Failure Therapy

Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com

Long-Term Therapy for Heart Failure
When the heart is not able to pump out the volume of blood it receives (backward failure) or cannot pump out enough blood to supply oxygen to the body (forward failure), the goal is to avoid or resolve a life-threatening crisis. Once the short-term disaster is resolved, we look to a more long-term therapy plan.

The Basics of Short-Term Heart Failure
In the short term, the body has an assortment of mechanisms to preserve circulation to the heart and brain and keep blood pressure up. The problem is that these mechanisms evolved for protection against blood pressure drop due to bleeding (as in predator attack). Protection against heart failure is an added benefit in the short term but in the long term problems arise.

So let’s say blood pressure drops. It could be because a predator has taken a bite out of a large blood vessel and there is bleeding or more relevant to the topic of this discussion, it could be because the heart is not moving an adequate quantity of blood forward. Either way the tissues of the body need more blood supply and they need it quickly. What does the body do?

Neurologic reflexes are activated that cause the heart to pump faster and stronger to move the maximum blood with each contraction.

Antidiuretic hormone and aldosterone (an adrenal hormone) are released telling the kidney to hang on to every last sodium atom it sees. Where there is sodium, there is water and water (blood is mostly water) is the medium through which supplies reach our tissues and wastes are removed from our tissues. If we are going to have adequate blood, we need adequate water and that means hoard sodium.

A hormone system called the renin-angiotensin system kicks on to produce a material called Angiotensin II. Angiotensin II is one of the strongest vasoconstrictors known to science. It closes off vessels supplying non-essential areas preserving circulation for the heart and brain, which must be kept perfused at all costs.
So, in short, our heart works harder, our vessels close off, and we retain salt. This is all wonderful but if the heart is weak, it cannot handle the extra blood volume brought on by retaining salt, nor can it push blood through constricted vessels or continue pumping faster and harder all the time.

Long-Term Heart Failure Management
Managing the failing heart is all about creating a balance for what a sick heart can handle and lifting the burden created by the protective mechanisms of the crisis. Our patient should be comfortable and able to perform modest exercise. We want to minimize discomfort due to coughing, fluid build-up, or collapse.

Diuretics
A diuretic is a drug that increases urine production. Diuretics are life-saving in a heart failure crisis where the lungs are filling with fluid because the heart cannot pump blood in quantities large enough to prevent fluid build-up. The dose needed for long term comfort is highly individual and may change depending on the stage of disease. Furosemide is almost always the first diuretic used as it is one of the most powerful. It is often used in combination with an ACE inhibitor for long term therapy.

ACE Inhibitors
ACE stands for angiotensin converting enzyme. We briefly mentioned the renin-angiotensin system above. Angiotensinogen is an inactive product made by the liver. It circulates all the time and converts to a substance called Angiotensin I at a rate so slow as to be completely innocuous. When blood pressure drops, special receptors in the kidney detect the drop and release a hormone called renin. Renin is a catalyst. It makes the conversion of Angiotensinogen to Angiotensin I happen much faster to create a large amount of circulating Angiotensin I. The final activation occurs in the lung where ACE converts Angiotensin I to Angiotensin II, completing the transformation from Clark Kent to Superman.

During an emergency we need Superman but on a day to day basis we want less Superman and more Clark Kent.

By using medication to inhibit ACE, we get less sodium retention and we keep blood vessels open. When the heart is overwhelmed by the amount of blood it is asked to pump forward (i.e., it receives more blood than it can pump out), it is very helpful to dilate peripheral blood vessels. Another analogy might involve a freeway system or turnpike with an inefficient tollbooth. Opening up more side streets, reduces traffic on the main freeway. Opening up peripheral blood vessels means less blood volume for the overloaded heart to pump.

Ace inhibitors help dilate the blood vessels but are not very potent relative to some other medications. Your veterinarian may prescribe other drugs, such as hydralazine or amlodipine, to accomplish this.

Disadvantages
One of the effects of the ACE inhibitor is reduced blood flow through the kidney. The kidney’s normal function depends on receiving good blood flow. If not monitored by checking blood tests that tell us about kidney function soon after starting ace inhibitors, kidney function may suffer from ACE inhibitor use particularly when it is combined with diuretics (as it usually is for heart failure) thus necessitating monitoring tests for kidney function. ACE inhibitors can also drop blood pressure excessively and may lead to retention of potassium.

Digoxin
Dogs are sometimes (less often today than in years past) prescribed digoxin in combination with the above medications. It yields several benefits:

It causes the heart to pump slightly stronger and more efficiently without pumping faster.
It reduces certain types of rhythm disturbances.
It reduces stimulation by the sympathetic nervous system to reduce heart rate.

The biggest down side is what is called a narrow therapeutic range. This means that there isn’t much leeway between a dose that helps and a toxic dose. Blood levels must be regularly monitored. Upset stomach can be a side effect. Concurrent use of certain other drugs can influence the strength of any given dose of digoxin so it is important for your veterinarian to know of all medications your pet is taking. Pets with kidney disease are most susceptible to the risk of developing these side-effects of too much digoxin.

Other Things That Might Help
Sodium Restriction
In most heart failure scenarios, the heart is unable to handle the blood volume with which it is presented. Fluid backs up and leaks out, creating either fluid in the lung (pulmonary edema) or fluid build up in the belly. In the long term, the last thing we want is to retain sodium and give the heart more blood volume to pump.

A sodium restricted diet is helpful in relieving some of the heart’s burden if the pet will eat it. Some theapeutic diets are restricted in sodium but they are so very bland, many pets will not accept them. Diets made for kidney disease are used and generally found more palatable. Using purified water for drinking may also help as many areas contain water with high sodium levels.

Poor appetite bodes poorly in heart failure as does loss of muscle tone. One must balance the blandness of the low sodium diet with keeping the pet’s appetite up.

The benefits of a sodium restricted diet do not outweigh the negative effect on health and quality of life if your pet doesn't eat or enjoy eating. The most important point here is to avoid very salty foods (pretzels, potato chips, processed ham, etc). If your pet with heart failure enjoys a sodium restricted diet, that is great. If not, feed the diet they enjoy and accept that you might need to give a bit more of the diuretic (see below) to control their heart failure.

Omega 3 Fatty Acids
Supplementation with omega 3 fatty acids is currently being researched as a possible treatment for the drastic weight loss (cardiac cachexia) that occurs with some cases of heart failure. If a pet enjoys these fishy flavored supplements, it may be a particularly helpful way to encourage appetite.

Activity Restriction?
People often ask how much restriction in exercise they should impose. Some exercise is good for the pet’s well-being and life quality. Avoid exercise that leads to excessive panting or weakness.

Learn How to Check Your Pet’s Respiratory Rate
A patient with heart failure distress will have an increased respiratory rate. A pet with controlled heart failure may have a respiratory rate that is greater than normal. It is very helpful to know what is normal for your pet and check several times daily. Simply watch the number of chest excursions during a 15-second period. A change in respiratory rate is a good sign the pet needs a check up with the vet. With cats, be sure the cat is not purring when respiratory rate is checked. Do not count panting for dogs.

This work was originally published by Veterinary Information Network, Inc. (VIN)
and is republished with VIN's permission.

The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.