Transcript Chapter_049
Principles of Electrocardiography Chapter 49 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 1 Learning Objectives Define, spell, and pronounce the terms listed in the vocabulary. Apply critical thinking skills in performing patient assessment and care. Illustrate the electrical conduction system through the heart. Explain the concepts of cardiac polarization, depolarization, and repolarization. Summarize the properties of the electrocardiograph. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 2 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. Compare and contrast electrocardiograph artifacts and the probable cause of each. Identify a typical electrocardiograph tracing. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 3 Learning Objectives Describe common electrocardiograph arrhythmias. Summarize cardiac diagnostic tests. Apply a Holter monitor. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 4 The Cardiac Cycle The cardiac cycle includes all of the events occurring in the heart during one single heartbeat. Systole Diastole The electrocardiograph records both the intensity and the actual time it takes for each part of the cardiac cycle to occur. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 5 Heartbeat Origin The sinoatrial (SA) node controls the rate of heart contraction by initiating electrical impulses every 60 to 100 times per minute. The heart beats in response to an electrical signal that originates in the SA node in the right atrium, spreads over the atria, and causes atrial contraction. This impulse continues to the atrioventricular (AV) node, through the bundle of His, and then through the right and left bundle branches, eventually causing ventricular contraction. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 6 Cardiac Rhythms Normal sinus rhythm (NSR) refers to a regular heart rate that falls within the average range of 60 to 80 beats/min Sinus bradycardia is a heart rate less than 60 beats/min A rate of greater than 100 beats/min is called sinus tachycardia An irregular cardiac rhythm is called an arrhythmia. Conditions that interrupt the conduction pathway, SA node to AV node to bundle of His to right and left bundle branches, can cause arrhythmias. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 7 Electrical Conduction System From Hunt SA: Saunders fundamentals of medial assisting, Philadelphia, 2002, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 8 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 9 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 10 The ECG Machine Six-channel ECG machines – Leads placed at specific anatomic locations; records all 12 leads automatically and marks each lead with identifying letters; multichannel ECG tracings take seconds to perform and can be placed into chart without mounting Single-channel ECG machines – Older machines that record the 12 leads one at a time; strips must be cut apart and mounted onto a card before placement in the chart Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 11 Critical Thinking Application Martha has not been taught how to use the ECG machine in Dr. Lee’s office. What steps should she take to learn how to use this machine and feel comfortable and confident using it to obtain ECGs? Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 12 Sample ECG Machines From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 13 Electrocardiograph Paper The horizontal lines on the ECG paper permit the determination of the intensity of the electrical activity or the relative strength of the heartbeat. The paper is heat and pressure sensitive; it must be handled carefully to avoid making any additional markings that would blemish the tracing. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 14 Paper Record The horizontal axis of the paper represents time and the vertical axis represents amplitude Each small square measures 1 mm on each side Every fifth line, both vertically and horizontally, is darker than the other lines creating a larger square measuring 5 mm on each side One small 1-mm square passes the stylus every 0.04 second; one large 5-mm square passes the stylus every 0.2 second; in 1 second, 5 large squares pass the stylus Large squares represent 0.2 second; 5 of them equals 1 second; ECG paper travels past the stylus at 25 mm per second Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 15 ECG Paper From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 16 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. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 17 Lead Recordings Each lead records the electrical activity of the heart between two different electrodes, one positive and one negative If depolarization occurs toward the positive electrode the deflection is upright; if it moves toward the negative electrode it is deflected downward ECG records views of the heart on both a frontal and a transverse plane Frontal leads include leads I, II, III, aVR, aVL, and aVF. Horizontal plane leads include the six precordial or chest leads Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 18 Standard Leads The first three leads recorded are called the standard or bipolar leads; they each use two limb electrodes to record the heart’s electrical activity 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 19 Augmented Leads Unipolar leads with a single positive electrode that uses the right leg for grounding aVr – records the electrical activity of the atria from the right shoulder; P waves and QRS complexes are deflected below the baseline 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 surface of the left ventricle from the left leg Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 20 Standard and Augmented Leads From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 21 Precordial Leads Transverse plane view of the heart; QRS complex is a negative deflection in V1 and V2, views with each subsequent lead becoming more positive Measure the electrical activity among six specific points on the chest wall and a point within the heart Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 22 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. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 23 Chest Leads From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 24 Electrode Placement Courtesy CompuMed, San Diego, Calif. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 25 Critical Thinking Application Dr. Lee has asked Martha to perform her first ECG on a patient who just came into the office. Martha is not confident that she knows how to properly place the chest leads in the correct location. How should she handle this situation? Should she perform the ECG procedure “the best that she can”? Why or why not? Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 26 Preparation of Room and Patient Pick the quietest location in the office, as far away as possible from all electrical equipment Patient should empty the bladder and rest for at least 10 minutes Patient should disrobe to the waist; gown open in front; pantyhose removed and limbs exposed Supine position with pillows to support head, back, and under knees If patient is in a seated position the feet must rest comfortably on the floor or on a footstool; record any alternative position Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 27 Preparation of Patient Record vital signs and current medications on the medical record or ECG Explain the procedure and purpose of the ECG Make the patient as comfortable as possible Stress importance of not moving during entire procedure; observe that he or she is breathing normally Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 28 Apply Electrodes and Leads Applying leads to the patient Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 29 Recording an ECG—Procedure 49-1 Enter specific information about the patient including age, sex, prescriptions, etc. After the ECG is programmed, remind the patient to lie still and press the appropriate key to run the ECG strip Six-channel machines will print and label all 12 leads with a rhythm strip across the bottom of the paper in lead II in a matter of seconds Review the printout; if acceptable give it to the physician Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 30 Standardization, Sensitivity, and Speed Stylus should deflect exactly 10 mm when the standardization button is depressed with a quick pecking motion Most machines have three sensitivity standards that can be selected If QRS complex is too tall the STD should be set to 1/2 STD; if QRS complex is too short the STD should be set to 2 STD Usual speed for an ECG recording is 25 mm/sec Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 31 Sensitivity Standards Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 32 Mounting an ECG Tracing The facility will select the mount that is best suited to the type of ECG equipment used in that particular office Paper clips and staples are never used; they scratch and mark a tracing; tape should not be used because it yellows with age A photocopy can be made of the tracing and placed in the medical record With electronic medical records the tracing is scanned into the patient’s record Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 33 Labeling ECG Strip Patient’s full name, sex, age Date and time of ECG List of all medications and/or supplements Variations from normal sensitivity and normal speed A very nervous or anxious patient Lack of rest before test Smoking immediately before test Failure to follow any pretest instructions Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 34 Telephone Transmission An ECG machine can transmit a recording over a telephone to an interpretation center Recording is interpreted by a computer at the data center and verified by a cardiologist Patient information that is important to interpretation such as medications and vital signs sent with the ECG Printout with interpretations returned to sender by fax or email Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 35 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 36 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 37 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. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 38 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. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 39 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 Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 40 Critical Thinking Application Dr. Lee asks Martha to explain to her the causes of artifacts and the methods for correcting ECG recordings that show outside interference. Based on what you have learned about ECG artifacts, what are the typical causes, and how would you recommend correcting each? Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 41 Normal ECG Appearance Table 49-2 NSR – each beat of the heart is initiated with an impulse from the SA node that then travels, without interruption, along the normal conduction pathway of the heart Each beat of the heart shows a P wave followed by a QRS complex Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 42 Rate and Rhythm To calculate heart rate count the number of P waves in a 6-second strip (30 large squares) and multiply by 10 Ventricular contraction rate – count the number of complete QRS complexes in 6 seconds and multiply that number by 10 to get the number of contractions in 1 minute If the patient’s heart is in a regular rhythm each cardiac cycle occurs within the same time frame and each cardiac cycles occur exactly the same length of time apart Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 43 Typical Rhythm Abnormalities Sinus rhythm – heart’s electrical activity begins in the SA node and follows through the electrical system, ending in atrial and ventricular depolarization Sinus arrhythmias – pathway of the electrical charge is normal but the rate or rhythm of the heartbeat is altered Sinus bradycardia – heart rate less than 60 beats/min Sinus tachycardia – heart rate more than 100 beats/min Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 44 ECG Rhythm Abnormalities Atrial arrhythmias Premature atrial contraction (PAC) – atria contract before they should; show up as abnormally shaped P wave or an extra P Atrial flutter – extremely rapid atrial rate, up to 300 beats/min Ventricular arrhythmias Premature ventricular contraction (PVC) – ventricles contract before they should; QRS complex appears before P wave Ventricular tachycardia – (V-tach) 101 to 250 beats/min Ventricular fibrillation – (V-fib) life-threatening arrhythmia; heart muscle quivering uncontrollably; unable to pump blood; there is no pulse Asystole – no heartbeat; flatline on ECG Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 45 Rhythm Abnormalities From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 46 Biochemical Arrhythmias Digitalis – causes scooping of ST segment in V5 and V6 From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby. Potassium – hyperkalemia or hypokalemia can both cause life-threatening arrhythmias Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 47 Pacemaker Rhythm Pacemakers stimulate the electrical activity of the heart Implanted under the skin; it is a small metal pulse generator with a battery and electronic leads that extend from the generator to the myocardium Programmed to fire according to individual patient needs Readings transmitted over phone From Lewis S et al: Medical-surgical nursing, ed 7, St Louis, 2007, Mosby. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 48 Implanted Cardioverter Defibrillator (ICD) Monitors heart rhythm and delivers shock to the heart if it detects a dangerous tachycardia or fibrillation A small, battery-operated device that is implanted under the skin in the chest or abdomen Can reverse V-tach and V-fib, especially after the patient has had an MI Generator programmed to treat the patient’s particular or potential cardiac arrhythmia Patient can telephone in periodic readings Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 49 Myocardial Infarction Causes specific ECG changes based on the phase that the patient is in when the ECG is recorded (Table 49-4). Three most common changes – elevated ST segments, inverted (upside-down) T waves, and abnormal (pathological) Q waves. From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 50 MI Treatment Sooner treatment is initiated the more effective and the better the patient outcome Immediate treatment – nasal oxygen, sublingual nitroglycerin (to dilate coronary arteries), narcotic analgesic (to eliminate pain), aspirin (to reduce inflammation and decrease clotting time), and possibly a thrombolytic agent to dissolve the clot in the coronary arteries After discharge – quit smoking, modify diet, enter cardiac rehabilitation program to improve cardiac strength and recovery by exercise Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 51 Cardiac Stress Test Conducted to observe and record the patient’s cardiovascular response to measured exercise challenges. Courtesy Cardiac Science Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 52 Critical Thinking Application Mr. Sonderford actually had an MI when he was previously at Dr. Lee’s office. He has now completed cardiac rehabilitation and is at the office for a checkup. Dr. Lee wants him to be scheduled for a stress test. Mr. Sonderford has never had one before. He confides to Martha that he is afraid if he takes the test, he will die from another heart attack. How should Martha handle this situation? Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 53 Holter Monitor A portable system for recording the cardiac activity of a patient over a 24-hour period or longer. Courtesy Welch Allyn, Skaneateles Falls, NY. 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. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 54 Critical Thinking Application Mrs. Jamison was fitted with a Holter monitor at the office yesterday at 4 pm. When Martha arrived at the office at 8 o’clock this morning, she found Mrs. Jamison had left a message with the answering service to call her as soon as possible. When Martha returned the call, she told her she took a shower last night and she noticed when she got up to go to the bathroom that the “light is not on” on the monitor. How should Martha handle this situation? Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 55 Cardiac Event Monitor Recording device that can be worn up to 30 days to catch events that are difficult to record in a 24-hour Holter monitor period Patients trigger the recording when feel any symptoms Remove during bathing – patient must be taught how to remove and reapply the electrodes Patient education – do not alter lifestyle; record activities when events occur; change electrodes daily and batteries at the same time each day; instructions on how to transmit recordings by phone Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 56 Electron Beam Tomography Heart Scan (EBT) Noninvasive method of assessing possible cardiac risk Takes less than 5 minutes and does not require any needles or injections Records amount of plaque present in coronary arteries by showing the presence of calcium deposits Calcium makes up approximately 20% of arterial plaque deposits The patient’s calcium score can predict future cardiac problems Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 57 Patient Education Heart disease and stroke account for more than one-third of all deaths. Talk to the patient about factors that could be modified, and give him or her encouragement for any attempt at complying with these suggestions. Include visual aids, posters, and brochures. Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved. 58