Congestive heart failure (CHF) is the clinical syndrome of fluid retention due to severe heart disease.
In dogs and cats, the fluid is retained in specific parts of the body, depending on the diseased side of the heart. The left side of the heart brings oxygenated blood to the body; the right side brings blood to the lungs, where it becomes oxygenated.
The heart should be seen as an amazing pump and seems complicated to understand initially; however, once seen as a mechanical device that moves blood to different body parts, it can be demystified.
CHF occurs because the pressure in the veins and capillaries draining into the diseased side of the heart increases to the point that fluid leaks out of the veins and capillaries. The capillaries and veins that drain into the left side of the heart are those coming from the lungs, so fluid leaks into the lungs. The capillaries and veins that drain into the right side of the heart come from the body, so fluid leaks into the belly (ascites) or creates swelling in the legs, the skin under the belly. Swelling of the legs or the skin is uncommon in dogs and cats with right-sided CHF, but much more common in humans and horses.
It can be useful to think of this like a garden soaker hose. If water flows through the hose under low pressure, only a little water leaks through the soaker hose. However, if we increase the pressure inside the hose, water starts to emerge from the soaker hose much faster and floods your garden.
The same happens with the capillaries – under low pressure, only a little fluid leaks out of them, but if the pressure is too high, a large volume of fluid leaks out into the surrounding tissue and overwhelms the ability of the body to absorb the fluid.
CHF requires severe heart disease that increases the resting cardiac pressure. For example, diseases that cause leakage of valves, like mitral or tricuspid valve disease, can result in CHF if the leak is big enough. Pericardial diseases can prevent the heart from relaxing and stretching properly, which can result in right-sided CHF. Heartworm disease can cause right-sided CHF. Many congenital defects that shunt blood can result in CHF like patent ductus arteriosus, ventricular or atrial septal defects. Congenital diseases that obstruct outflow from the heart, , do not normally cause CHF.
The clinical signs of CHF depend on the diseased side of the heart. As fluid starts to deposit fluid into animals’ lungs, the amount of oxygen in the blood decreases because it can’t be absorbed from the lungs. Human patients describe this as shortness of breath, initially during exertion, such as climbing stairs, and eventually even when stationary.
However, animals cannot tell us if they are short of breath. Sometimes, owners will notice a decrease in exercise ability, such as not going as far on walks and getting winded on walks more quickly. Keep in mind many things can cause exercise intolerance.
Coughing has been described as a feature of CHF in dogs, but there is some doubt as to whether CHF really causes coughing or not. Again, many dogs and cats cough for reasons other than heart disease. As the fluid continues to build up, dogs and cats will also show difficulty breathing and a faster respiratory rate. This is especially true of cats, who can hide their disease until it becomes advanced. Consequently, many cats see veterinarians with labored, open mouth breathing that is almost gulping for air, which appears to have started suddenly. In dogs, the clinical signs can be more gradual and subtle.
With right-sided CHF, the most common presentation is a swelling of the abdomen (ascites), making the dog appear pregnant. The discomfort from a belly full of fluid results in difficulty getting comfortable or breathing comfortably when lying down. These dogs will even resort to sleeping in a sitting position at times! Appetite often decreases slightly because of abdominal pressure. If there is a fluid buildup in the chest cavity, the animal might show difficulty breathing.
The diagnosis of CHF relies on pairing the clinical signs of increased respiratory rate and difficulty in breathing with the severe heart disease responsible for these clinical signs. Many times, a murmur can be heard for the first time. The pet’s heart rate will be elevated; their respiratory rate will be elevated. Some cats come in with a low body temperature because they are somewhat shocked from inadequate oxygen.
If I suspect CHF, I will take chest X-rays to see if there is evidence of severe heart disease that appears as an enlarged heart; and look for areas through which light does not pass in the lungs consistent with pulmonary edema or fluid in the chest cavity consistent with pleural effusion. I might recommend a cardiac ultrasound if I am unsure or require additional information. Those are often performed by specialists who have the necessary equipment, typically veterinary cardiologists or radiologists.
Treatment is directed at the underlying heart disease and fluid accumulation. If possible, the cause should be corrected. Repairing a leaking mitral valve will correct the problem almost immediately, although this procedure is currently very expensive and performed by a limited number of surgeons.
The mainstay of medical treatment of left-sided CHF is using certain diuretics, such as lasix. Diuretics reduce blood volume and the pressure in the veins, forcing the fluid out into the lungs or the abdomen.
Other drugs are less effective than diuretics and should never be given as the only drugs for managing CHF. If a dog or cat does not require a diuretic, they most likely do not have CHF.
The fluid buildup in right-sided CHF often requires repeated manual removal, using large catheters to make the patient feel better. In many dogs, this can be done as frequently as every week or two. Ideally, when coupled with medical treatment, the frequency of belly taps can be reduced somewhat.
The most important thing to monitor with left-sided CHF is respiratory rate. Provided the respiratory rate when sleeping is in the normal range, we can reasonably assume that we have good control of the CHF. When the sleeping respiratory rate starts to increase, adjustments in treatment might be necessary; a veterinarian will evaluate the patient to determine exactly what to do. Many veterinarians will monitor bloodwork to ensure that the medications are not causing problems with kidneys or elsewhere. If a pet appears to destabilize after a period of control, additional x-rays might help better evaluate the situation.
The prognosis depends somewhat on the underlying disease. With the more common diseases, such as mitral valve disease in dogs or hypertrophic cardiomyopathy in cats, once CHF is diagnosed and treatment instituted, survival is generally less than two years. With mitral valve disease, approximately 50 percent of dogs will succumb to their disease within eight to 10 months, and only 20 percent live for 18 to 24 months. With hypertrophic cardiomyopathy, survival data are less clear, but some older studies suggest that 50 percent of cats will succumb to the disease within seven to 10 months. As always, a few individuals will live longer than expected.