Body Parts – the Feline Heart
The heart is the main organ in the circulatory system. Its job is to pump blood throughout the body, supplying oxygen and nutrients to the tissues. Similar to the human heart, the feline heart has four chambers. The two chambers on the top of the heart are the atria (plural for atrium). The two chambers at the bottom of the heart are the ventricles. The left atrium and left ventricle are separated from the right atrium and right ventricle by a dividing wall called the septum.
Listening to your cat’s heart with the stethoscope is one of the most important parts of the veterinary exam. The normal heart rate in a cat is 160 to 240, which is much faster than a human’s. Cats are often nervous during the veterinary visit, so it’s not unusual to find heart rates in the 200’s. The rhythm should be regular and the heartbeat should be easily heard. Abnormalities in the heart rate and rhythm are fairly uncommon. The most common abnormality heard with the stethoscope is a heart murmur. A murmur is the sound of turbulent blood flow and may be an indicator that something is amiss.
Coronary artery disease is the most common cause of death in humans in the U.S. Fortunately, cats don’t get coronary artery disease. Nature, however, doesn’t play favorites when it comes to other heart diseases, and cats are indeed susceptible to disorders of this vital organ. Therefore, the discovery of a heart murmur during your cat’s physical examination warrants further investigation. It can be difficult for a veterinarian to know just by listening whether a feline heart murmur is merely a physiologic finding (i.e. there’s actually nothing wrong with the heart), or a pathologic finding (i.e. there is indeed something wrong with the heart). Physiologic murmurs are benign and can be caused by things such as stress, excitement, pain, or fever. The only way to tell if a murmur is benign vs. pathologic is to perform echocardiography (sometimes also called a sonogram, or cardiac ultrasound).
Echocardiography is best performed by a veterinary cardiologist. (Yes, there are veterinarians that specialize in cat and dog tickers only.) These cardiologists know exactly how thick or how thin the walls of each heart chamber is supposed to be, how fast the blood should be flowing as it travels out of the aorta and pulmonary artery, and how strongly the heart is supposed to be contracting. By viewing the heart using ultrasound and taking a variety of measurements, the cardiologist can determine if heart disease is present.
The most commonly diagnosed heart disease in cats is a condition called hypertrophic cardiomyopathy (HCM). In cats suffering from HCM, the walls of the heart become progressively thicker, with one particular chamber, the left ventricle, usually becoming the most affected. Think of the left ventricle as a coffee mug. Now imagine the walls of the mug becoming thicker and thicker, growing inwardly. The mug would hold less and less coffee. In HCM, the ventricle holds less and less blood. If the ventricle can now hold only half as much blood, the heart will try to compensate by pumping twice as hard to achieve the same effect. Eventually, the muscle starts to give out, and congestive heart failure may develop. Other complications, however, may arise before heart failure ever develops. The most serious complication of HCM is a condition called aortic thromboembolism, abbreviated ATE. In ATE, a blood clot develops in the left atrium. A piece of the blood clot breaks free, travels down the aorta, and gets lodged at the very end, where the aorta branches to supply the legs with blood. Cats become acutely paralyzed in the rear legs as a result. This is a truly devastating complication that carries a very grave prognosis. Sadly, as a feline practitioner, I have the terrible misfortune of seeing two or three cases of ATE a year, and every case ends disastrously. Sigh. Cats diagnosed with HCM are usually prescribed a variety of medications aimed at slowing the progression of the disorder and reducing the risk of ATE, and many cats do well for many years after the diagnosis with no symptoms at all.
HCM can strike any breed of cat, however, Maine Coons and Ragdolls are predisposed to the disorder. Fortunately, the reason for their susceptibility was discovered several years ago: a mutation in the gene that codes for a specific protein in the heart. A genetic test has been developed to screen cats for the disorder. The test requires either a cheek swab or a blood sample. Responsible breeders can now test their cats for this mutation, and use selective breeding techniques to hopefully eliminate the gene from the population.
Kittens will sometimes have a heart murmur that disappears as they mature. A persistent murmur in a kitten, however, should be investigated, as congenital heart diseases occasionally do occur, and the sooner they are diagnosed and treated, the better the prognosis.