Feline Cardiovascular System

Part of the feline cardiovascular system protecting the feline heart is the pericardium which shields the heart from friction and inflammation. It stabilizes the heart’s position in the chest cavity and maintains its shape. The feline heart has four chambers with valves that regulate blood flow. The major veins bringing blood to the heart are called vena cavas. Blood first enters the heart’s right atrium, then passes through the tricuspid valve and flows into the right ventricle. The right ventricle contracts and sends blood into the pulmonic artery through the pulmonic valve. Blood then goes to the lungs where it becomes oxygenated. Oxygenated blood from the pulmonic vein enters the heart’s left atrium, then passes into the left ventricle via the mitral valve. When the left ventricle contracts, blood shoots out of the heart through the aorta and circulates throughout the rest of the body. This entire cycle, regulated by the sinoatrial node, continues without pause. The sinoatrial node acts as the pacemaker, sending out electrical impulses that trigger the heart muscle to contract. It is rare for cats to have problems with these pacemakers. The feline cardiovascular system is complex.

The feline cardiovascular system heart responds to electrical and nervous system stimulation as well. When a cat is at rest, circulation is relaxed. But when a cat exercises the heart rate increases, blood pumps faster throughout the body, more oxygen replenishes the cells and more deoxygenated blood returns to the heart. Hormones and other chemicals within the body also affect heart output. Adrenaline stimulates the heart to pump faster so the feline can react more quickly. The left ventricular heart muscle wall is three times as thick as the right ventricular wall. This is due to the distance that the heart must send the blood. The right side sends blood only into the lungs, but the left side must push blood throughout the entire circulatory system. The tricuspid and mitral valves regulate blood flow through the heart.

In the feline cardiovascular system, deformities of these valves are the most common congenital cardiac malformations. A murmur, or squishing sound, indicates flood is leaking out of the valves during heart contraction. Instead of forming a tight seal, blood escapes around the valve. By listening to the heart with a stethoscope vets can often detect valve problems. A murmur’s intensity and loudness does not correlate with the severity of valve damage. Murmurs are very common in older cats. Some kittens are born with murmurs and outgrow them while others have murmurs all their lives and experience no problems. Though uncommon in cats, some murmurs may progress and lead to congestive heart failure.

The feline cardiovascular system has heart muscle diseases that are more common from acquired disease than congenital problems. Three forms of heart muscle disease may develop in cats: dilated cardiomyopathy, hypertrophic cardiomyopathy and restrictive cardiomyopathy. All of these conditions affect the heart muscle’s function if the pump breaks down, proper circulation cannot occur. When the amino acid taurine is deficient in cats, they are more prone to developing dilated cardiomyopathy. When this was discovered in the late 1980’s, it led to the reformulation of all cat foods so they would contain a higher level of taurine. Increasing the daily recommended allowance of taurine intake has greatly reduced this type of heart disease. Unfortunately, feline heart muscle disease can be difficult to regulate with medications so most often the disease progresses and results in heart failure.

In the feline cardiovascular system another condition associated with improper heart muscle function is thrombus formation. A thrombus is a blood clot that can pass through the large blood vessels but can become lodged in smaller vessels. When a clot lodges, the blood supply is cut off and paralysis can occur. Tissues deprived of their blood supply will eventually die. Even if a veterinarian is successful in dissolving the clot with medications, recurrences or progression of heart muscle dysfunction is likely.

Yet another section of the feline cardiovascular system is the muscular band called the diaphragm which separates the chest cavity from the abdominal cavity. Defects in muscles that surround body cavities are called hernias. Cats suffer two major types: diaphragmatic hernias and peritoneal-pericardial diaphragmatic hernias. The former occurs as a result of trauma, the latter is a congenital defect. When the diaphragm no longer separates the body cavities, abdominal organs move forward in the chest cavity and put pressure on the heart and lungs. Symptoms of either type of hernia include shortness of breath, difficulty breathing, rapid heart rate, heart arrhythmia, gastrointestinal upset, weight loss or general discomfort. Some cats, especially those born with the defect, show very few signs. As they grow and live with the defect, they learn to compensate. Another condition that can affect the heart is bacterial endocarditis, a heart valve infection that can lead to serious problems, even permanent valve deformity. These are all conditions of an ailing feline cardiovascular system.

Cats can also contract heartworms from mosquito bites. Heartworms are infrequent in cats as compared to dogs due to a cats increased resistance to infection and minimal exposure to mosquitoes that carry the heartworm………more details on HEARTWORM.

Because in the scheme of the feline cardiovascular system the feline heart is relatively small, diagnostic testing is difficult. In animals with larger hearts, vets can isolate areas of the heart with auscultation. Electrocardiograph measurements in cats produces small complexes that can be a challenge to interpret. Cardiac sonograms is the best diagnostic tool available to assess heart function and appearance. X-rays of the heart tell vets about the heart’s size and shape, but not how the blood is being pushed through. Ultrasound allows visualization and measurement of the individual heart chambers, valves and major blood vessels. It can also document cardiac output and blood-flow problems. This information is critical to diagnose cardiomyopathy and also can measure response to drug therapy.

Measuring feline blood pressure is fairly routine. The highest pressure, called systole, occurs when the heart contracts. The lowest pressure, called diastole, occurs when the heart relaxes. Hypertension can lead to over stimulation of the heart muscle, which might wear out prematurely and eventually fail. Controlling blood pressure in cats means the underlying disease must first be controlled or drugs may be used.

In the feline cardiovascular system the cat’s circulatory system carries heat, hormones, drugs, nutrients and oxygen throughout the system. The blood-brain barrier prohibits many substances in the blood from entering the cerebral spinal fluid and central nervous system. The rest of the body directly or indirectly receives substances from the circulating blood. A 10 pound cat has a blood volume of about 10 fluid ounces. Each of the blood’s components…plasma, red blood cells, white blood cells and platelets…has a specific task. The bone marrow stores immature blood cells until they are needed. There are five cell types that constitute white blood cells. Neutophils are the most numerous white blood cells in cats that are healthy. Neutophils kill microorganisms by engulfing them. Monocytes engulf microorganisms, but they also secrete inflammatory and immunologic substances. Eosinophils are specialized cells that battle parasites and certain allergic conditions. Basophils, an uncommon type of feline white blood cell are mediators of inflammation. There are two types of lymphocytes: B cells which are responsible for producing antibodies and T cells which are responsible for cell-mediated immunity. Certain diseases will trigger certain types of white blood cells to react.

Platelets are another crucial component of the blood because they aid in clotting. They create a mechanical block and serve as a catalyst for the coagulation cascade that completes proper clotting. Red blood cells are called crythrocytes. In a normal cat they make up about 35 percent of the blood. The red blood cells contain hemoglobin, which is responsible for carrying oxygen. Oxygen-rich blood is bright red while poorly oxygenated blood is dark. Though red blood cells are only one component of the blood, they are responsible for all of the red color.

Anemia is a low red blood cell count and can be life-threatening. Tissues that do not receive enough oxygen and nutrition cannot function properly. There are many causes of anemia. It can result from excessive bleeding and losing a lot of blood. It can occur if an animal is flea-infested and is drained of blood by the parasites. Anemia can also result from poor nutrition or long term disease. It can occur when drugs or cancer suppress the bone marrow, which contains the immature blood cells. A red blood cell parasite called Hemobartonella can affect cats. This organism enters red blood cells and causes them to destruct within the cat’s body. Regional parasites can also cause anemia. The treatments for anemia are aimed at the specific causes. A blood transfusion acts as a temporary fix until the animal’s body can regenerate enough replacement cells. Cats have two major blood types which are A and B. In North America 98% of the cats have type A blood. Type B blood is most often seen in certain purebred cats including the British Shorthair, Devon Rex, Cornish Rex, Abyssinian and Somali. Diseases that affect other types of blood cells also exist. Pure leukemias are not uncommon in cats. Leukemia is an over-proliferation of a white blood cell line. It is not common for the feline leukemia virus to actually cause blood-cell leukemia because it is more common for it to cause anemia.