There has been an explosion of information regarding the formation of bioelectrical energy and its interplay in the electrical conduction system through many disciplines of science. This has led to the development of a new subspecialty of cardiology known as electrophysiology (EP) or electrophysiology studies (EPS). At its core, EPS deals with arrhythmias.
This chapter introduces the concept of ionic flow through the cell membrane and the formation of bioelectrical energy. It is essential that we understand that cells depolarize (“fire”) and repolarize (“reload”) by the movement and concentration of either positively or negatively charged ions through a semipermeable membrane. The firing of the cells allows for cell-to-cell transmission, which spreads the sequential depolarization of sheets of cells, bundles of muscles, and, eventually, the entire organ.
We now clearly understand that there are various small channels that are found along the cell membrane. These channels are controlled by the voltage gradient that is maintained during the steady state or opened during the depolarization–repolarization process. These channels allow for massive amounts of ions to flow from one side of the membrane to the other, causing the voltage changes required to fire or recharge the cell. The complete study of this process is beyond the scope of this book, and you are encouraged to study it further in physiology books or on the Internet.
For now, let’s say that these genetically coded channels can be expressed as normal variants or abnormal variants. The abnormal variants are known as the channelopathies. EPS research has identified a significant number of these mutations, many of which can lead to the formation of arrhythmias or transmission problems. An example of these defects, which we will review in greater depth later in the book, includes the association between the prolongation of the QT interval, the Romano-Ward syndrome, and torsade de pointes. Various channelopathies have been linked to these disorders, which shows a strong association of cause and effect for the formation of these life-threatening arrhythmias.
You may be asking yourself: “But I’m not an electrophysiologist—why is this important to me?” You do not have to know all there is to know about channelopathies, but you do have to know a little about them. It is becoming increasingly clear, as EPS advances, that the understanding and manipulation of the properties of these channels is a critical aspect to the future evaluation and treatment of the arrhythmias. In addition, genetic counseling and monitoring may help save countless lives in the long run.
I can hear some of you saying: “Does this affect my clinical practice on a day-to-day basis?” Well, it really doesn’t alter your ability to grossly identify a rhythm on a strip. However, it does keep you from making serious mistakes that could injure or kill your patient. Remember, mechanisms are the key to understanding. Here’s another way of looking at it: Does it help if I call you up and tell you there’s a cat in your house? What if I neglected to mention the type of cat—that a breakout at the zoo resulted in the escape of man-eating tigers? I would not be wrong in stating I warned you. Nor would you be wrong in pointing out from your hospital bed that cats can be anything from cute little fur balls to saber-tooth tigers. As we will point out throughout this book, you always want as much information as you can get. Always look at the company it keeps. If it hangs around with trouble, it will eventually find you.
—Daniel J. Garcia