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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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Electrode leads on the chest wall are able to detect electrical impulses that are generated by the heart. Multiple leads provide many electrical views of the heart. By interpreting the tracing, the physician can learn about the heart rate and rhythm as well as blood flow to the ventricles (indirectly).

Rate refers to how fast the heart beats. Normally, the SA node generates an electrical impulse 60-100 times per minute. Bradycardia (brady=slow+cardia=heart) describes a heart rate less than 60 beats per minute. Tachycardia (tachy=fast+cardia=heart) describes a heart rate faster than 100 beats per minute.

Rhythm refers to the type of heartbeat. Normally, the heart beats in a sinus rhythm with each electrical impulse generated by the SA node resulting in a ventricular contraction, or heartbeat. There are a variety of abnormal electrical rhythms, some are normal variants and some are potentially dangerous. Some electrical rhythms do not generate a heartbeat and are the cause of sudden death.

Rhythm strip showing a normal 12-lead ECG.

Examples of heart rhythms include:

• Normal sinus rhythm
• Sinus tachycardia
• Sinus bradycardia
• Atrial fibrillation
• Atrial flutter
• Ventricular tachycardia
• Ventricular fibrillation

There can also be delays in transmission of the electrical impulse anywhere in the system, including the SA node, the atria, the AV node, or in the ventricles. Some aberrant impulses cause normal variants of the heart rhythm and others can be potentially life threatening. Some examples include:

• 1st degree AV block
• 2nd degree AV block, type I (Wenckebach)
• 2nd degree AV block, type II
• 3rd degree AV block or complete heart block
• Right bundle branch block
• Left bundle branch block

There can also be short circuits that can lead to abnormal electrical pathways in the heart causing abnormalities of rate and rhythm. Wolfe-Parkinson-White (WPW) syndrome is a condition where an abnormal accessory pathway at the AV node causes tachycardia.

The ECG tracing can also provide information about whether the heart muscle cells are conducting electricity appropriately. By analyzing the shape of the electrical waves, the physician may be able to determine if there is decreased blood flow to parts of the heart muscle. The presence of an acute blockage associated with a myocardial infarction or heart attack can be determined as well. That's one of the reasons that an ECG is done as soon as possible when a patient presents with chest pain.

Must Read Articles Related to Electrocardiogram (ECG)

Angina Pectoris Angina pectoris is a term to describe chest pain that occurs when the heart is not getting enough blood. There are two types of angina, stable (the most common)...learn more >>

Atrial Fibrillation Atrial fibrillation (A fib) describes a rapid, irregular heart rhythm. The irregular rhythm, or arrhythmia, results from abnormal electrical impulses in the hea...learn more >>

Atrial Flutter Atrial flutter is an abnormality in the beating of the heart. Such abnormalities, whether in rhythm of heartbeat or speed of heartbeat, are known as arrhythmias...learn more >>

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