Basic ECG Theory, 12-Lead Recordings, and Their Interpretation
The recorded electrocardiogram (ECG) remains as one of the most vital monitors of a patient’s cardiovascular status and is used today in nearly every clinical setting. This chapter discusses the ECG as a measure of how the electrical activity of the heart
- PDF / 1,294,369 Bytes
- 14 Pages / 595.28 x 790.87 pts Page_size
- 86 Downloads / 223 Views
19
Sarah Vieau and Paul A. Iaizzo
Abstract
The recorded electrocardiogram (ECG) remains as one of the most vital monitors of a patient’s cardiovascular status and is used today in nearly every clinical setting. This chapter discusses the ECG as a measure of how the electrical activity of the heart changes over time, as action potentials within each myocyte propagate throughout the heart during each cardiac cycle. By utilizing the resultant electrical fields present in the body, electrodes can be placed around the heart to measure potential differences as the heart depolarizes and repolarizes. Furthermore, various techniques for obtaining ECG data are presented. Electrocardiography has progressed rapidly since it was first employed back in the early 1900s. New instruments that are smaller and more sophisticated, as well as innovative analysis techniques, are continually being developed. The trend has been toward developing smaller, easier-to-use devices that can gather and remotely send a wealth of information to aid patient diagnosis and treatment. Keywords
Electrocardiogram • ECG waveform • 12-Lead ECG • ECG placement • ECG recording devices • Holter monitor • Loop recorder
19.1
The Electrocardiogram
An electrocardiogram (ECG) is a measure of how the electrical activity of the heart changes over time, as action potentials within each myocyte propagate throughout the heart as a whole during each cardiac cycle. In other words, the ECG is not a direct measure of the cellular depolarization and repolarization, but rather the recording of the cumulative signals produced by populations of cells eliciting changes in their membrane potentials at a given point in time. The ECG
S. Vieau, MS (*) Medtronic, Inc., 8200 Coral Sea Street NE, MVN61, Minneapolis, MN 55112, USA e-mail: [email protected] P.A. Iaizzo, PhD Department of Surgery, University of Minnesota, Minneapolis, MN, USA
provides specific waveforms of electrical differences when the atria and ventricles depolarize and repolarize. The human body can be considered, for the purposes of an ECG, as a large volume conductor. It is filled with tissues surrounded by a conductive medium, in which the heart is suspended. During the cardiac cycle, the heart contracts in response to action potentials moving through the chambers of the heart in a coordinated fashion. As this normally occurs, one part of the cardiac tissue is depolarized and another part is at rest or polarized. This results in a charge separation, or dipole, which is illustrated in Fig. 19.1. The moving dipole causes current flow in the surrounding body fluids between the ends of the heart, resulting in fluctuating electric fields throughout the body. This is much like the electric field that would result, for example, if a common battery was suspended in a saltwater solution (an electrically conductive medium). The opposite poles of the battery would cause current flow in the surrounding fluid, creating an electric field that could be detected by electrodes placed in the solution. A
© Sprin
Data Loading...
