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2 The Electrocardiogram Fast & Easy ECGs, 2nd E – A SelfPaced Learning Program Fast & Easy ECGs, 2E 1 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electrocardiogram • An electrocardiogram is a tracing of the heart’s electrical activity • An electrocardiograph is the machine that produces it Fast & Easy ECGs, 2E 2 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electrocardiograph • Also called the ECG machine, it detects heart’s electrical activity through electrodes positioned on patient’s skin I Fast & Easy ECGs, 2E 3 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Machines • A variety of ECG machines are available – Some monitor from one to five different leads – Some are capable of monitoring up to twelve or more leads simultaneously – Some are used for continuous monitoring I Fast & Easy ECGs, 2E 4 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. The Input • Lead wires and cables transfer the ECG signal detected through the electrodes to the ECG machine – There may be 3, 4, or 5 lead wires for monitoring purposes and up to 10 lead wires for 12-lead ECGs – Each lead wire has a labeled clip, snap, or pintype connector on the distal end which attaches to the electrode I Fast & Easy ECGs, 2E 5 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Using Lead Wires and Cables • Keep the lead wires separated from each other to avoid tangling • Position them loosely across the patient so they do not pull on and lift the electrodes away from the skin • Properly clean and decontaminate then after each use I Fast & Easy ECGs, 2E 6 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Electrodes • Are typically disposable • Consist of a: – wet or dry electrolyte gel (which acts to assure good signal pick-up), – metal snap or tab (where the ECG lead wire is attached), – self-adhesive pad that holds the electrode to the skin Self-adhesive pad Electrolyte gel Metal snap I Fast & Easy ECGs, 2E 7 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Placing ECG Electrodes • To achieve a noisefree recording: – Clean the skin site to remove dead skin cells and oils – Clip dense hair present at the sites where the electrodes are to be placed I Fast & Easy ECGs, 2E 8 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Placing ECG Electrodes • Eliminate muscle tension by placing the patient’s arms and legs in a comfortable position in which the extremities are resting on a supportive surface – If artifact is still present and the patient tolerates it, try laying him or her in a flat position Fast & Easy ECGs, 2E 9 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Placing Electrodes • Avoid removing electrodes from their sealed protective envelope before use as the conductive gel may dry • With snap-on lead wires, attach the electrode to the lead wire before placing the electrodes onto the patient’s skin • With clip-on type lead wires, apply the connector to the metal snap of the electrode after the electrode has been placed I Fast & Easy ECGs, 2E 10 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Placing Electrodes • Place the electrodes in the correct locations – Know where each electrode is supposed to be positioned – Look for a flat surface and sites over soft tissues – Avoid areas where large bones are near the skin surface and areas where there are thick muscles or skin folds Fast & Easy ECGs, 2E 11 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Leads • Are a combination of electrodes that form an imaginary line in the body along which the electrical signals, detectable during the time course of the heartbeat, are measured I Fast & Easy ECGs, 2E 12 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Leads • Each lead provides a different view of the heart: – Electrodes are placed on chest, arms and legs – Sites vary depending on which view of the heart's electrical activity is being assessed Fast & Easy ECGs, 2E 13 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Leads • Deflection of the waveforms seen on the ECG depend on where the positive electrode is placed in comparison to the direction of the electrical forces I Fast & Easy ECGs, 2E 14 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Leads • ECG leads are either bipolar or unipolar Fast & Easy ECGs, 2E 15 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Bipolar Leads • Record the flow of the electrical impulse between two (one is positive, the other is negative) selected electrodes • Includes I, II and III Fast & Easy ECGs, 2E 16 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Bipolar Leads • Record difference in electrical potential between a positive and negative electrode • Uses a third electrode called a ground • Include leads I, II and III Fast & Easy ECGs, 2E I 17 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Unipolar Leads • Use only one positive electrode and a reference point calculated by the ECG machine • Includes leads aVR, aVL, aVF, and V1 through V6 Fast & Easy ECGs, 2E 18 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Planes of the Heart • Electrodes are placed on the extremities and chest wall to view the heart’s electrical activity from the frontal and horizontal planes – Provides a crosssectional view of the heart Fast & Easy ECGs, 2E I 19 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Frontal Plane • Leads that view this plane are called limb leads • Include leads I, II, III, aVR, aVL and aVF • Provide inferior, superior, and lateral views of heart Fast & Easy ECGs, 2E 20 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Horizontal Plane • Leads that view this plane are called precordial or chest leads • Include leads V1, V2, V3, V4, V5, and V6 • Provide inferior, superior, and lateral views of heart Fast & Easy ECGs, 2E 21 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Different Leads Uses • A given lead may be used to highlight: – A specific part of ECG complex – Electrical events of a specific cardiac cycle – Conditions such as an enlargement of heart muscle or presence of ischemia, injury and infarction I Fast & Easy ECGs, 2E 22 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Limb Lead Locations • RA electrode – positioned anywhere on the right arm or below the right clavicle in the midclavicular line • LA electrode – positioned anywhere on the left arm or below the left clavicle in the midclavicular line • LL electrode – positioned anywhere on the left leg or left midclavicular line below the last palpable rib • RL electrode – positioned on the right leg or right midclavicular line below the last palpable rib Fast & Easy ECGs, 2E 23 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Chest Leads • Positioned in order across the chest Fast & Easy ECGs, 2E 24 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Lead II • ECG electrode polarity – Positive electrode – LL lead wire – Negative electrode – RA lead wire – Ground electrode – LA lead wire (and RL lead wire) • Produces positively deflected waveforms Fast & Easy ECGs, 2E 25 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. The Output • ECG machine translates the electrical impulses generated in the heart into wave-like signals that are recorded on paper or displayed on a monitor Fast & Easy ECGs, 2E 26 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Oscilloscope • ECG rhythms displayed on the oscilloscope are called dynamic ECGs • Represent real time electrical activity or what is presently occurring in the heart Fast & Easy ECGs, 2E 27 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Printouts • ECGs printed on graph paper are called static ECGs • Show what has already occurred • Much easier to analyze a static ECG to identify abnormalities than it is to examine an image moving across a screen I Fast & Easy ECGs, 2E 28 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Printouts • As the stylus moves across the moving ECG paper it inscribes waveforms representing the heart’s electrical activity • Vertical lines on the ECG paper represent amplitude in electrical voltage while horizontal lines represent time or duration Fast & Easy ECGs, 2E I 29 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. ECG Paper • Each small square equals – 0.04 sec in duration and 0.1 mV in amplitude • Five small squares (1 large box) equals – 0.20 seconds in duration I Fast & Easy ECGs, 2E 30 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Isoelectric Line • Is the flat line that occurs when no electrical activity is occurring or impulses are too weak to be detected • Used as a baseline to identify changing electrical movement Fast & Easy ECGs, 2E 31 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Calibration or Registration Mark • Helps ensure ECG machine is properly calibrated • Serves as reference point on ECG tracing I Fast & Easy ECGs, 2E 32 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Artifact • Markings on ECG tracing that are not a product of heart’s electrical activity – Patient movement is among its many causes – Can mimic lifethreatening dysrhythmias I Fast & Easy ECGs, 2E 33 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Summary • Graphic record or tracing is called an electrocardiogram while the machine that produces it is called the electrocardiograph • Electrodes placed on patient’s skin detect heart’s electrical activity • Abnormalities in cardiac rate and/or rhythm are called dysrhythmias Fast & Easy ECGs, 2E 34 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Summary • Each lead provides a different view of heart. • Impulses traveling toward a positive electrode are recorded on ECG as upward deflections. • Impulses traveling away from a positive electrode or toward a negative electrode are recorded as downward deflections. Fast & Easy ECGs, 2E 35 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Summary • Limb leads are produced by placing electrodes on right arm (RA), left arm (LA) and left leg (LL). – Include leads I, II, III, augmented vector right (aVR), augmented vector left (aVL) and augmented vector foot (aVF). • Precordial leads include leads V1, V2, V3, V4, V5, and V6. Fast & Easy ECGs, 2E 36 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Summary • ECG paper consists of horizontal and vertical lines that form a grid. • Horizontal measurements used to determine heart rate and duration of various waveforms, segments and intervals. • Vertically on ECG paper, distance between lines, or boxes, represents amplitude in millimeters (mm) or electrical voltage in millivolts (mV). Fast & Easy ECGs, 2E 37 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Summary • Calibration • Artifact is markings on ECG tracing that have no relationship to electrical activity of the heart. Fast & Easy ECGs, 2E 38 © 2013 The McGraw-Hill Companies, Inc. All rights reserved.