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Cardiomyopathies: When a heart gets broken

February and Valentine's Day and I usually think of cupid and arrows with little hearts on the end of them. Unfortunately, in reality the old ticker doesn't always function like it should (and I'm not talking about poor Charlie Brown and waiting for a letter from the girl with the red hair) and one group of diseases that affect the heart is termed cardiomyopathies.

Cardiomyopathies are disorders associated with the heart muscle. The term cardiomyopathy originates from "cardio" meaning heart, "myo" referring to muscle and "pathos" which is associated with suffering or disease. Cardiomyopathies are very dangerous because of the very special job the heart does and the unique tissue that makes up this organ.

The heart is not only a muscle, but also an electrical system. In addition, the electrical portion of the heart does not require any conscious effort to work and resets itself automatically. If a pet (or ourselves for that matter) needed to think about each heart beat before it actually happened they'd be dead. Before discussing pathology, or disease of the heart, a good review of the normal anatomy and physiology of a healthy heart is in order.

The dog or cat heart is divided into four chambers (just like a human's heart) with two upper chambers called the right and left atria, and two lower chambers called the right and left ventricles. Blood enters the right side of the heart from the body through the right atrium, into the right ventricle, and is pumped up to the lungs. Once blood is in the lungs, carbon dioxide is released and oxygen is bound to hemoglobin (a special protein on red blood cells that carries oxygen). The blood then travels back to the heart via the left atrium, to the left ventricle, and then out the aorta to provide vital oxygen and nutrients to the body.

A healthy heart starts beating with a small electrical discharge that begins from what are called nodes. Nodes are specialized tissues in the heart wall that act as pacemakers, or the areas that initiate the electrical impulse to start the heart contracting (beating).

There are two nodes in the heart that initiate the electrical charge necessary to keep the heart beating. The first node is called the sinoatrial, or SA node and is located in the right atrium (upper right chamber) of the heart. Once the electrical charge is initiated from the SA node the myocardium, or heart muscle, carries the charge down to the atrioventricular, or AV node. The AV node is located in the interventricular septum, or heart wall that separates the two ventricles (lower chambers). This second charge carries electricity through the heart muscle that surrounds the ventricles and causes them to contract.

I hope this first article highlighted both the electrical and muscular systems of a healthy heart in dogs and cats. My next article will discuss the two most common types of cardiomyopathies in dogs and cats, as well as the diagnosis and treatment of these diseases.

Dr. Kearns has been in practice for 12 years and is pictured with his son Matthew, as well as the newest member of the family, Jasmine, a Labrador retriever.

Author: 
Matthew Kearns, DVM