Basic electrocardiogram interpretation for perioperative nurses - Home Study Program

AORN Journal, Oct, 2003 by Bettyman Hutchinson, Shirley Cossey, Rose Marie Wheeler

The article electrocardiogram interpretation for perioperative nurses" is the basis for this AORN Journal independent study. The behavioral objectives and examination for this program were prepared by Rebecca Holm, RN, MSN, CNOR, clinical editor, with consultation from Susan Bakewell, RN, MS, education program professional, Center for Perioperative Education.

Participants receive feedback on incorrect answers. Each applicant who successfully completes this study will receive a certificate of completion. The deadline for submitting this study is Oct 31, 2006.

Complete the examination answer sheet and learner evaluation found on pages 593-594 and mail with appropriate fee to

AORN Customer Service

c/o Home Study Program

2170 S Parker Rd, Suite 300

Denver, CO 80231-5711

or fax the information with a credit card number to (303) 750-3212.

You also may access this Home Study via AORN Online at http://www.aorn.org/journal/homestudy/default.htm.

BEHAVIORAL OBJECTIVES

After reading and studying the article on basic electrocardiogram interpretation, perioperative nurses will be able to

1. identify the components of the conduction system of the heart,

2. describe lead placement to perform electrocardiography,

3. explain how the coronary blood supply can affect arrhythmias, and

4. use assessment and rate calculations to interpret rhythm strips.

Editor's note: This article is an updated reprint of the electrocardiogram Home Study published in the AORN Journal in January 1999.

Historically, monitoring and interpreting electrocardiograms (EKGs) intraoperatively have been the responsibility of anesthesia care providers. Changes in health care, however, frequently have required that perioperative nurses assume this responsibility. Today, perioperative nurses are expected to manage an increasing number of patients undergoing IV conscious sedation who require EKG monitoring. Perioperative nurses also may be expected to be cross trained to the postanesthesia care unit (PACU) and preoperative holding areas. Positive patient outcomes are related to their ability to monitor and interpret patients' EKGs.

THE CONDUCTION SYSTEM

An EKG is a road map of the electrical activity of cardiac cells during the contraction and relaxation of the heart. The sinoatrial (SA) node, atrioventricular (AV) node, and Purkinnje fibers are the normal pacing sites of the heart (Figure 1). In a healthy person, an EKG should demonstrate an organized, sequential electrical impulse from its beginning at the SA node to its conclusion at the Purkinje fibers. Cardiac electrical activity immediately precedes the contraction of cardiac muscle.

[FIGURE 1 OMITTED]

Normal electrical conduction of the heart begins in the SA node, located in the right atrium. The SA node is the natural pacemaker of the heart and has an intrinsic rate of 60 to 100 beats per minute (BPM). Without any other stimulation, the SA node has the ability to initiate an impulse. An impulse initiated by the SA node travels through the atria via the intranodal pathways. This results in depolarization (ie, contraction) of the atria.

The impulse then travels from the atria to the AV node, where it is delayed for 0.08 to 0.12 seconds. This delay allows both atria to depolarize before the impulse continues through the remaining conduction system pathway. The AV node blocks excessive atrial impulses from reaching the ventricles, thus preventing cardiac output from dropping to dangerous levels as a result of a fast ventricular rate. The AV node also has the ability to act as the pacemaker for the heart should the SA node fail or the impulses from the SA node become blocked.

The cardiac impulse then travels from the AV node to the Bundle of His, which divides into right and left bundle branches that travel to the ventricles. The cardiac impulse terminates with ventricular depolarization, which takes place in the Purkinje fibers located in the muscles of the ventricles. Cardiac dysrhythmias are caused by disturbances in automaticity (ie, the ability of a cell to generate electrical impulses spontaneously) or conductivity (ie, the ability of the cell to conduct electrical impulses) or an alteration in both.

ELECTROCARDIOGRAPHY

The EKG, a tracing of the electrical activity in the heart, is recorded on heat-sensitive graph paper (Figure 2). Time is measured horizontally, and voltage is measured vertically. On the EKG graph paper, one small square is equal to 0.04 seconds in time. One large square contains five of the small squares and, therefore, is equal to 0.20 seconds (ie, 5 x 0.04 seconds). A complete cardiac cycle (ie, one polarization and depolarization of the heart) is represented on the EKG by the letters P, Q, R, S, and T. Interval measurements (ie, PR, QRS, QT) on the EKG assess the length of time it takes an impulse to travel through the heart (Figure 3).

[FIGURE 2-3 OMITTED]

LEAD PLACEMENT. Electrocardiography records the flow of electrical currents of the heart as they move away or toward a specific electrode. Standard lead placement uses leads I, II, and III, forming Einthoven's Triangle. This equilateral triangle is named for Willem Einthoven, the man responsi ble for developing the first set of leads used to record electrical activity of the heart. Leads I, II, and III record the flow of electrical current by using the limb leads as positive or negative poles. Lead I is used to record electrical activity at the left lateral wall of the heart. Lead II is the most commonly used lead and is used to record the flow of electrical activity in normal atrial and ventricular depolarization. Lead III provides information about the inferior wall of the heart. Current flowing toward the positive electrode records an upright deflection on the EKG tracing, and current flowing away from the positive electrode records a downward, or negative, deflection.