Congestive heart failure can be a devastating disease for both dogs and cats, striking primarily older and obese animals. To properly understand this condition it is important to know how the heart functions. Dogs and cats, like humans, have a four-chambered heart. The top two chambers are called the atria, the bottom two are the ventricles. Each atria and ventricle are separated by an AV valve, preventing blood from flowing from the ventricles to the atria. Blood enters the atria and the atria contract, pushing the blood into the ventricles. When the ventricles contract, blood is pushed out of the heart and travels to the body's tissue through arteries. This is why there are two heart sounds, a lub and a dub, for every heart beat.
There are four causes of congestive heart failure.
- Myocardial Failure: the ventricles don't contract strongly enough, so the blood isn't pushed out of the heart with enough force. This can be caused by: drug toxicities, not enough blood or oxygen to the heart, the chambers are too large, infection or inflammation, or persistent abnormal heart rhythms.
- Volume Overload: there is too much fluid in the heart. This can be caused by: leaky valves, valve degeneration, inflammation of heart valves, chronic anemia, or toxins.
- Pressure Overload: when a higher then normal blood pressure is needed to eject blood, which results in the heart becoming too large due to the increased work load. This can be caused by: high-blood pressure, narrowing of the vessels, or heartworm disease.
- Reduced Ventricular Compliance: the ventricles aren't able to fill all the way. This leads to abnormal function, congestion and diminished output. Reduced ventricular compliance can be caused by heart disease, and too much fluid in the sac around the heart, which interferes with the heart's performance.
It is possible to have left-sided, or right-sided heart failure, or both. The symptoms of heart failure vary depending on which side it is occurring.
Symptoms of Left-Sided Heart Failure
- a violent cough, especially at night or early morning
- difficulty breathing, especially due to exercise or lying down
- fainting
The cough usually occurs because of fluid in the lungs, or because the left atrium is compressing the left bronchus. Fainting or syncope results from decreased blood flow to the brain.
Symptoms of Right-Sided Heart Failure
- an enlarged liver, or spleen
- fluid in the abdomen, the lungs, in the sac surrounding the heart, and in the sub-cutaneous tissue space, which causes difficulty breathing
- high central venous pressure, distended jugular vein
Congestive heart failure is diagnosed by symptoms, and x-ray and ultrasound, which look for fluid accumulation and an enlarged heart.
There is no cure for congestive heart-failure. The goal of treatment is to improve cardiac output, reduce the heart's workload, control excess fluid in the tissues, lungs, abdomen, and around the heart, and manage abnormal heart rhythms.
When an animal comes in to the veterinarian in sudden and severe heart failure, it is placed in strict cage confinement and receives oxygen by an oxygen cage, face mask, or oxygen tubes in its nose. They are given medications to help remove excess fluid, re-distribute blood volume, and reduce constricted bronchi. Excess fluid in the chest, abdomen, and around the heart may also be drained to ease difficulty breathing. Animals may be sedated to minimize anxiety, and any complications are carefully monitored and managed.
Dogs and cats being managed for congestive heart failure at home are on restricted diets and exercise to help reduce the workload on the heart and control fluid accumulation. They may also be placed on diuretics to help reduce fluid in the lungs and around the heart. Once they have been diagnosed with congestive heart failure, it is up to the owner to decide whether and how long to treat their pet for this disease, taking into account the pet's quality of life.
Nelson R and Couto C. Manual of Small Animal Internal Medicine. St Louis Mo: Mosby, 1999.
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