The electrocardiogram (EKG) is an important tool that is used to evaluate heart health. The technician is responsible for the administration of the exam and needs a basic understanding of EKG rhythms to determine whether or not the exam has been completed properly and to perform an initial evaluation of the results. Individuals who put forth the effort to learn about the different types of rhythms and what they mean will discover that they enjoy higher levels of career satisfaction and are in a better position to provide comprehensive care.
A standard electrocardiogram is administered using cables that are commonly referred to as ‘leads.’ The leads are designed to detect voltage differences between electrodes and transmit information to the recorder so that a visual representation of the differences can be created. The typical 12-lead EKG uses ten electrodes that include RA, LA, RL, LL, V1, V2, V3, V4, V5, and V6. Additional leads can be added in an effort to evaluate EKG rhythms that require greater sensitivity. As current passes through the heart, the EKG recorder traces a series of waves and intervals that are used to evaluate the health of the heart. In general, technicians should expect to see a P wave, QRS complex, T wave, and a U wave. In many cases, the U wave may not be visible because of overlap with the T and P waves.
Normal EKG rhythms include a normal sinus rhythm in which each P wave is followed by a QRS complex and occur at a rate of 60 to 100 beats per minute. If the P waves occur less frequently then the patient is said to have sinus bradycardia; whereas, if they occur more frequently then the patient is said to have sinus tachycardia. A standard P wave should have a height of less than 2.5mm and a width less than 0.11mm in Lead II. A healthy EKG also shows a QRS complex that is less than 0.12s and a PR interval between 0.12 and 0.20s. There should be no elevation or depression of the ST segment and the T wave should be of normal height. Variations in the size, shape, or duration of any of the waves or segments could be a sign of a heart problem.
One of the most concerning EKG rhythms is one that indicates that a portion of the heart has died because it has gone without oxygen supply for a period of time. This condition is commonly known as a heart attack or a myocardial infarction and it occurs when a cardiac artery has been blocked. Because electrical current in the heart does not travel through dead tissue, the location of the infarction can be isolated using an electrocardiogram. A myocardial infarction causes an ST elevation in different leads depending on where it has occurred. An elevation in leads II, III, and aVF indicate that damage has occurred in the lower portion, an elevation in V1 – V6, I, and aVL indicate that damage has occurred in the front portion, and a tall R and T wave in leads V1 – V3 may be an indication that damage has occurred in the back portion of the heart.
Some other types of common EKG rhythms that a technician might encounter are the result of an enlarged heart that is often due to inefficient pumping of blood. This can be caused by increased resistance in outbound blood vessels, incompetent valves, and a variety of other problems. There are a number of different criteria for interpreting these types of rhythms and it is generally beyond the scope of practice for a technician to attempt an interpretation of these rhythms. The main thing to recognize with these tracings is that the R and S segments are typically greater than 25mm. In the event that the mitral valve has become stenotic, a technician may recognize the condition due to a lack of P waves and an irregularly irregular rhythm. If the P wave is greater than 2.5mm in lead II then it may be an indication that the patient is experiencing enlargement of the right atrium.
In some situations, the electrical current that is traveling in the cardiac tissue may not be conducted from the atria to the ventricles. In this case, the patient suffers from heart block. An EKG that shows intermittent conduction of P waves is usually an indication of heart block. 2 to 1 AV heart block occurs when every other P wave is transmitted. If the P waves occur randomly it might be a sign of complete heart block. Since the ventricles can create their own current, they will undergo depolarization even when the AV node is not working.