Electrocardiography - Zohomycollege.zohosites.com/files/14. Electrocardiography.pdf · EKG Leads...

Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Electrocardiography


Learning Objectives

• Describe the electrical views of the heart recorded by the 12-lead electrocardiograph.

• Discuss the process of recording an electrocardiogram.

• Perform an accurate recording of the electrical activity of the heart.

• Discuss electrocardiograph artifacts.

• Prepare a patient for an EKG.


Electrocardiogram

ECG (EKG):

• The electrocardiogram (ECG) is a diagnostic tool that measures and records the electrical activity of the heart in detail.

• An EKG translates the heart's electrical activity into line tracings on paper.


Why is it Done? • Check the heart's electrical activity.

• Find the cause of unexplained chest pain.

• Find the cause of symptoms of heart disease, such as shortness of breath, dizziness, fainting.

• Check how well medicines are working and whether they are causing side effects that affect the heart.

• Check how well mechanical devices that are implanted in the heart, such as pacemakers, are working to control a normal heartbeat.

• Check for arrhythmia. (An irregular cardiac rhythm)


Sample ECG Machines

From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders.


EKG Leads and Electrodes • Lead refers to an imaginary line between

two ECG electrodes.

• The electrical activity of this lead is measured and recorded as part of the ECG.

• A 12-lead ECG records 12 of these “leads” producing 12 separate graphs on the ECG paper which are limb leads I, II, III, AVR, AVL, AVF, and Chest leads V1, V2, V3, V4, V5, and V6.

• However you only actually attach 10 physical electrodes to the patient.


Standard Leads I, II, and III

• The first three leads recorded on an EKG are called the standard or limb leads.

• Lead I records tracings between the right arm and left arm

• Lead II records tracings between the right arm and left leg; it is the lead recorded on a cardiac monitor or on the rhythm strip at the bottom of the 12-lead ECG

• Lead III records tracings between the left arm and left leg


Augmented Leads AvR, AvL, and AvF

• The second set of three leads that record on an EKG are called the augmented leads.

• AvR – records the electrical activity of the atria from the right shoulder.

• AvL – records the electrical activity of the lateral wall of the left ventricle from the left shoulder

• AvF – records the electrical activity of the inferior (lower) wall of the left ventricle from the left leg.


Standard and Augmented Leads

From Chester GA: Modern

medical assisting,

Philadelphia, 1999, Saunders.


Precordial Leads

• Chest leads V1-6 are called the precordial leads.

• Measure the electrical activity among six specific points on the chest wall and a point within the heart.


Precordial Lead Placement

• V1—the electrode is placed in the fourth intercostal space, just to the right of the sternum

• V2—the electrode is placed in the fourth intercostal space, just to the left of the sternum

• V3—the electrode is placed midway between V2 and V4

• V4—the electrode is placed in the fifth intercostal space, at the left midclavicular line

• V5—the electrode is placed horizontal to V4 in the left anterior axillary line

• V6—the electrode is placed horizontal to V4 in the left midaxillary line.


Electrode Placement

Courtesy CompuMed, San Diego, Calif.


Holter Monitor • A portable system for recording the cardiac activity of a

patient over a 24-hour period or longer.

• The patient must keep a journal of all stressful events and activities during the entire time the monitor is worn and press the event button if symptoms occur.

• A medical assistant is often responsible for instructing the patient in applying and removing the monitor.

Courtesy Welch Allyn,

Skaneateles Falls, NY.


Cardiac Stress Test

• Conducted to observe and record the patient’s cardiovascular response to measured exercise challenges.

Courtesy Cardiac Science


How to Prepare the Patient for an EKG • Pick the quietest location in the office, as far

away as possible from all electrical equipment.

• Wash your hands before and after EKG.

• Introduce yourself to the patient.

• Identify your patient.

• Explain the procedure and purpose of the ECG

• Make the patient as comfortable as possible

• Ask if she or he needs to empty their bladder.


Preparation of Patient • Have the patient disrobe to the waist; gown open in front. • Rest the patient in a supine position with a pillow to support head and

neck. • Proceed with alcohol prep and lead placement. • After the ECG is programmed, remind the patient to lie still. • Proceed with EKG recording. • Record vital signs, current medications, or patient activity on the ECG. • Review the printout; if acceptable give it to the physician.

• Stress importance of not moving during entire procedure; observe that he or she is breathing normally


Electrodes and Leads

• Two electrodes are placed on the arms and legs; six electrodes are placedon the chest

• Electrodes must be applied to specific locations to record the heart’s electrical activity from different angles and planes

• Most offices use single-use, self-stick, disposable electrodes that are packaged with conductive jelly in the center

• Ten color-coded and labeled lead wires ending in a small metal clip are attached to the electrodes

• The leads carry the cardiac electrical impulses into the machine.


Artifacts

• Erratic movement of stylus on ECG paper from outside interference

• ECG is extremely sensitive to any kind of nearby electrical activity

• Medical assistant should have thorough understanding of the causes of and remedies for artifacts


Wandering Baseline

Stylus gradually shifts away from center of paper

Caused by patient movement or poor electrode attachment

Remind patient to remain as still as possible; make patient more comfortable


Somatic Tremor

Any muscle movement produces a measurable electrical impulse causing stylus movement during the tracing

Shows up as jagged peaks of irregular height and spacing with a shifting baseline

Causes: patient discomfort, apprehension, movement, talking, or having a condition that causes uncontrollable body tremors.


Alternating Current (AC) Interference Appears as series of uniform small spikes

Electrical currents in nearby equipment or wiring can leak small amounts of electrical energy that the ECG picks up

Management – use three-pronged grounded outlet; do not cross lead wires; unplug other electrical appliances in room;

move table away from wall; and turn off fluorescent lights

From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby.


Interrupted Baseline Electrical connection is interrupted

Stylus moves erratically up and down across the paper, or it may record a straight line across the top or the bottom of the paper

Patient movement that dislodges electrodes causes most baseline interruption; also from broken lead wires or detached leads


Cardiac Contraction

• Polarization – resting state of the myocardial wall: no electrical activity in the heart; recorded on the ECG as a flatline

• Depolarization – contraction phase; electrical system of the heart stimulates the myocardium

• Repolarization – resting state after depolarization; the myocardium must return to a resting state before it can be electrically stimulated again


PQRST—Table 49-1 • P wave – first deflection from baseline; atrial

depolarization • PR segment – return to baseline after atrial contraction • PR interval – time from the beginning of atrial contraction

to the beginning of ventricular contraction • QRS complex – contraction of both ventricles • ST segment – time between the end of ventricular

contraction and the beginning of ventricular recovery • T wave – repolarization of the ventricles • QT interval – between the beginning of the QRS complex

through the T wave • U wave – occasionally seen as a small waveform after the

T wave


EKG Patterns

• Normal EKG:


EKG Patterns

• Bradycardia:


EKG Patterns

• Tachycardia:


EKG Patterns

• Ventricular Tachycardia:


EKG Patterns

• Myocardial Infarction:


EKG Patterns

• Asystole:


Rhythm Abnormalities

From Chester GA:

Modern medical

assisting, Philadelphia,

1999, Saunders.

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