Heart Disease (Coronary Artery Disease) Slideshow Pictures Medical Illustrations of the Heart Image Collection Take the Heart Disease Quiz!

Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

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Medical Editor:

Daniel Lee Kulick, MD, FACC, FSCAI

Daniel Lee Kulick, MD, FACC, FSCAI

Dr. Kulick received his undergraduate and medical degrees from the University of Southern California, School of Medicine. He performed his residency in internal medicine at the Harbor-University of California Los Angeles Medical Center and a fellowship in the section of cardiology at the Los Angeles County-University of Southern California Medical Center. He is board certified in Internal Medicine and Cardiology.

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Medical Editor:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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What Happens During an ECG?

The ECG is a relatively simple test to perform. It is non-invasive and does not hurt. Patches are placed on the skin to detect electrical impulses that the heart generates. These impulses are recorded by an ECG machine. Four patches are placed on the limbs. One is placed on each shoulder or upper arm and one on each leg. These are called the limb leads. There are six patches that are placed on the chest wall beginning just to the right of the breast bone. Patches are placed in the shape of a semi-circle ending near the left axilla (underarm). These are called the chest leads. These patches are connected to an ECG machine that records the tracings and prints them onto paper.

Newer machines also have video screens that help the technician, nurse, or doctor decide whether the quality of the tracing is adequate or whether the test should be repeated. ECG machines are also equipped with computer programs that can help interpret the ECG, although they are not completely accurate.

In certain situations, the physician may want to “look” at the heart from different angles after the initial ECG is done. The chest leads may then be placed across the right chest wall or on the back.

The skin should be clean and dry to prevent electrical interference to get an acceptable tracing for interpretation. Sometimes that means shaving chest hair or aggressively toweling off the skin. Shivering or tremors can interfere with the tracing and cause interference that affects the quality of the ECG tracing. Usually, the patient has to hold still for 5-10 seconds without moving to get an accurate ECG.