thaler chapter 1

Electricity and the Heart

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Cardiac cells can lose their internal negativity in a process called depolarization . Depolarization is the fundamental electrical event of the heart . In some cells, known as pacemaker cells, it occurs spontaneously. In others, it is initiated by the arrival of an electrical impulse that causes positively charged ions to cross the cell membrane. Depolarization is propagated from cell to cell, producing a wave of depolarization that can be transmitted across the entire heart. This wave of depolarization represents a flow of electricity, an electrical current, that can be detected by electrodes placed on the surface of the body. After depolarization is complete, the cardiac cells restore their resting polarity through a process called repolarization . Repolarization is accomplished by the membrane pumps, which reverse the flow of ions. This process can also be detected by recording electrodes. All of the different waves that we see on an EKG are manifestations of these two processes: depolarization and repolarization. Sometimes lethal disturbances in the conduction of electricity through the heart occur because of an inherited disorder of these transmembrane ion channels. Fortunately, these so-called channelopathies are quite rare. Many different genetic mutations affecting the cardiac ion channels have been identified, and more are being discovered every year.