Congestive heart failure, or CHF, is the end stage of almost any form of heart disease. While the underlying causes may vary, the effects are consistent and generally quite similar. If the underlying disease is incurable, CHF likewise cannot be “cured”; however, it can still be managed, to give your dog a comfortable and happy life.
What causes CHF?
A wide range of different heart conditions, but the most common are DCM (dilated cardiomyopathy) and endocardiosis (e.g. MVD, or mitral valve disease).
DCM is a condition characterised by swelling of the heart and thinning of its muscular walls. It is most common in large breed dogs such as Dobermans, Great Danes and Wolfhounds; however, it is occasionally seen as a result of poor diet in many other breeds.
Endocardiosis is a degenerative condition where the one-way valves in the heart start to leak. It is the most common cause of heart disease in dogs, and the valve most often affected is the mitral valve. Although any dog can be affected, small breed dogs are over-represented, especially Cavalier King Charles Spaniels.
Why does CHF happen?
Whatever the underlying cause, the result is that the heart becomes less efficient. This results in a drop in blood pressure, due to failure to pump the blood around the body as well. The failure to pump results in tissues becoming oxygen deficient (this is sometimes called “forward failure”), and pooling of blood upstream of the heart, as it isn’t being pumped forward well enough (also known as “backward failure”).
Moreover, the drop in blood pressure “tricks” certain systems in the dog’s body (the renin/angiotensin and aldosterone systems, or RAAS) into thinking that the dog is dehydrated, causing retention of water. In a dehydrated dog, or one in shock, this is a good protective reflex; however, in this case, the effect is occurring because the heart is unable to pump the blood that’s there efficiently; by increasing the amount of water in the bloodstream, it just makes matters worse.
What effect does it have on the dog’s body?
To some extent, it depends on which set of symptoms are predominant, although both sets will occur to some extent.
Forward failure results in blue gums, exercise intolerance, weakness and lethargy (as the muscles and other tissues are starved of oxygen), and sometimes even fainting.
Backward failure tends to be more obvious, and is associated with fluid building up in the abdomen (“ascites”, looking like a pot-belly) and the blood vessels of the neck (meaning that a pulse is visible in the neck in affected animals). However, most dangerous of all, it results in a build-up of fluid in the lungs, known as pulmonary oedema.
Why is this bad news?
Most dogs with heart failure die of drowning. As more and more water is retained in the body, and the heart is less and less able to pump it, the fluid accumulates in the lungs. Here, it obstructs the absorption of oxygen from the air, eventually suffocating the dog. This is why fast breathing rates, a cough, and difficulty breathing are major danger signs for heart failure.
Can it be treated?
Fortunately, yes it can! In a few cases, the underlying condition can be treated or cured, but normally, we focus on slowing down the deterioration, and managing the congestive heart failure. There are three major components to effective treatment:
- Diuretics, or water tablets. The most commonly used is furosemide (also known as frusemide), although spironolactone and, recently, torasemide, may also be used. These trigger water loss through the kidneys, pulling water out of the blood, and therefore out of the lungs. Diuretics keep the dog alive long enough for the other drugs to kick in!
- ACE Inhibitors help to deactivate the renin/angiotensin system, again reducing the fluid accumulation and helping to stabilise the dog’s blood pressure. Statistically, ACE inhibitors generally act to improve the dog’s quality of life.
- Positive Inotropes, e.g. pimobendan, are a class of drugs that help the heart beat more powerfully. These delay the onset of CHF, and slow down the progression of the disease, dramatically increasing the dog’s lifespan.