1. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Chapter 17 Interpreting the Electrocardiogram

2. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Learning Objectives Describe the value and limitations of the electrocardiogram (ECG). Describe the electrophysiology of cardiac cells. Describe how the cardiac impulse is conducted through the different structures of the heart. Recognize various abnormal ECG recordings. 2

3. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. The Electrocardiogram An ECG is a popular tool because it’s inexpensive, noninvasive, & easy to obtain Primarily used to assess patients suspected of having an acute myocardial condition Also used as health screening tool in patients over age 40 years Cannot predict future heart attacks or detect structural defects (e.g., valve stenosis) 3

4. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Electrophysiology Impulse-conducting system provides electrical stimulus to activate & pace myocardium Cardiac cells polarized with positive charge on the outside & negative charge on the inside When stimulated, cardiac cells depolarize as sodium rushes inside cells Depolarization causes muscle cells to contract momentarily Repolarization reestablishes electrical imbalance across cell membrane 4

5. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.5 An ECG may help to evaluate a patient for all of these conditions, except: A.Congestive heart failure B.Valvular defects C.Heart rate anomalies D.Myocardial Infarction

6. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Electrophysiology (cont.) Impulse-conducting system has 3 different types of cardiac cells capable of electrical excitation: 1.Pacemaker cells (e.g., sinoatrial node) 2.Specialized rapidly conducting tissue (e.g., Purkinje fibers) 3.Atrial & ventricular muscle cells All these cells have intrinsic ability to spontaneously depolarize (automaticity) 6

7. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Electrophysiology (cont.) 7

8. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. The Impulse-Conducting System This system is responsible for:  Initiating heartbeat  Controlling heart rate  Coordinating contraction of heart chambers A defect in system may lead to:  Inadequate cardiac output  Decreased tissue perfusion 8

9. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. The Impulse-Conducting System (cont.) Normally, SA node has greatest degree of automaticity & paces heart AV node serves as back-up pacemaker when SA node fails After leaving AV node, impulse travels through bundle of HIS, bundle branches, & Purkinje fibers. 9

10. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. The Impulse-Conducting System (cont.) 10

11. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.11 What is the purpose of the normally occurring, temporary delay of the electrical impulse at the AV node serve? A.Allows the ventricles time to fill with blood B.Increases ventricular stimulation C.Provides rest for the ventricles D.Allows the atria time to fill with blood

12. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. ECG Procedural Summary Physician order is required for 12-lead ECG Requires use of:  Portable ECG unit  Lead wires  Electrodes Placement of 12 leads (subdivided into 2 groups) 1.6 extremity (limb) leads 2.6 chest (precordial) leads 12

13. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. ECG Procedural Summary Limb leads are bipolar & are able to monitor heart’s activity that is directed up, down, left or right Precordial leads are unipolar & measure cardiac activity moving anteriorly or posteriorly ECG helps in diagnosis of certain heart conditions (myocardial infarction, cardiac ischemia 13

14. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Precordial Lead Placement 14

15. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Basic ECG Waves Atrial depolarization is seen as P wave Ventricular depolarization is seen as QRS complex Normal QRS complex is not wider than 3 mm (0.12 second) Wave of ventricular repolarization is seen as T wave 15

16. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Basic ECG Waves (cont.) PR interval is time from start of atrial contraction to start of ventricular contraction (normally not >0.20 second) Long PR intervals = heart block ST segment is time from end of ventricular depolarization to start of ventricular repolarization (normally isoelectric) Elevated or depressed ST segments = ischemia 16

17. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.17 Where can atrial repolarization be seen on an ECG tracing? A.During the ST segment B.It is obscured by the electrical activity of the ventricles. C.It is shown during atrial depolarization (P wave) D.It is obscured by the QT interval

18. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Basic ECG Waves (cont.) 18

19. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. ECG Paper & Measurement Grid-like boxes  Horizontal axis defines time  Vertical axis defines voltage Large box (5 mm) = 0.20 sec; small box (1 mm) = 0.04 sec 1 mV will cause an upward deflection of 10 boxes representing depolarization of ventricles 19

20. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. ECG Paper 20

21. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Interpreting the Electrocardiogram 1.Identify atrial & ventricular rates; normally, the same & 60 to 100/min. 2.Measure PR interval; normally, <0.20 second 3.Evaluate QRS complex; should be no longer than 0.12 second 4.Evaluate T wave; normally, should be upright & rounded; inversion = ischemia 21

22. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Steps to Follow (cont.) 5.Evaluate ST segment; normally, flat; significant elevation or depression = ischemia 6.Assess RR interval to evaluate regularity of rhythm 7.Identify mean QRS axis by finding limb lead with most voltage; if this lead has positive QRS complex, axis is very close to where this lead is labeled on hexaxial reference circle 22

23. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Hexaxial Reference 23

24. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.24 The QRS complex of an ECG falls on a dark vertical line on the ECG paper. The next QRS complexes fall on every third dark line (15 mm apart). What is the approximate ventricular rate? A.100 beats/min B.150 beats/min C.200 beats/min D.250 beats/min

25. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.25 All of these are possible conditions that may result from a patient’s QRS complexes measuring at 0.20 second, except: A.An impulse-conducting system abnormality within the ventricles B.A drop in cardiac output and blood pressure C.Patient may experience fainting spells D.An impulse-conducting system abnormality within the atria

26. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Axis Evaluation Helps determine general direction of current flow during ventricular depolarization to detect ventricular hypertrophy Normally, mean axis is between 0 & +90 degrees Right-axis deviation (+90 to +180 degrees) is consistent with right ventricular hypertrophy Left-axis deviation (between +90 and  90 degrees) is consistent with left ventricular hypertrophy 26

27. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.27 A patient’s mean QRS axis is +122 degrees on a hexaxial reference circle with a negative Lead I. This would suggest: A.Left-axis deviation B.Cor pulmonale C.Left ventricular hypertrophy D.Myocardial infarction

28. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Normal Sinus Rhythm Has an upright P wave identical throughout strip PR interval is <0.20 second QRS complexes are identical & no longer than 0.12 second ST segment is flat RR interval is regular & heart rate is 60 to 100/min 28

29. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Normal Sinus Rhythm (cont.) 29

30. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Sinus Tachycardia Recognized when heart rate exceeds 100/min at rest Each QRS complex is preceded by P wave Common finding in patients with acute illness & may be caused by pain, anxiety, fever, hypovolemia, & hypoxemia May also be caused by certain medications, such as bronchodilators Underlying cause must be treated 30

31. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Sinus Tachycardia (cont.) 31

32. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Sinus Bradycardia Heart rate is less than 60/min Each QRS is preceded by P wave PR interval & QRS complex are normal Of concern only when causing clinical problems, such hypotension & syncope Atropine is effective treatment 32

33. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Sinus Bradycardia (cont.) 33

34. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. First-Degree Heart Block PR interval exceeds 0.20 second Each QRS complex is preceded by P wave Cardiac impulse from SA node is delayed in passing through AV node or bundle of His Typically, RR intervals are regular May occur after MI or with use of beta-blockers Treatment may not be needed if patient asymptomatic 34

35. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. First-Degree Heart Block (cont.) 35

36. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.36 A patient is having symptoms of hypotension and occasional syncope. His ECG shows a heart rate of less than 60 beats/min. The tracing shows a QRS complex preceded by a P wave. What medication would be recommended to treat his condition? A.Atropine B.Beta blockers C.Digoxin D.Calcium channel blockers

37. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Second-Degree Heart Block Comes in 2 types:  Type I (Wenckebach or Mobitz type I) block; recognized when PR interval gets progressively longer until one does not pass on to ventricles  Type II (Mobitz type II) is: Less common Occurs with more serious problems, such as MI Seen as series of nonconducted P waves followed by P wave that conducts to ventricles 37

38. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Second-Degree Heart Block (cont.) Treatment for type I not usually needed Treatment for type II often requires medication, such as atropine & possibly pacemaker 38

39. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Second-Degree Heart Block (cont.) 39

40. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Third-Degree Heart Block Occurs when conduction system between atria & ventricles is completely blocked Atria & ventricles are paced independently & there is no relationship between P waves & QRS complexes PP intervals & RR intervals remain regular with no correlation with one another Treatment includes medications to speed up ventricles & placement of pacemaker 40

41. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Third-Degree Heart Block (cont.) 41

42. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Atrial Flutter Represents rapid depolarization of atria from ectopic focus (250 to 350/min) Causes characteristic sawtooth pattern; numerous P waves are present for each QRS Caused by wide variety of disorders, such as rheumatic heart disease, coronary heart disease, renal failure, stress, & hypoxemia Treated with medications & cardioversion 42

43. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Atrial Flutter (cont.) 43

44. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Atrial Fibrillation Results when atrial muscle quivers in irregular pattern; no true P waves are seen Ventricular rate may be slow & irregular Atrial fibrillation causes cardiac output to drop & may lead to thrombi in atria due to blood stagnation Cardioversion used as treatment in most cases 44

45. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Atrial Fibrillation (cont.) 45

46. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.46 A patient with a history of coronary heart disease, arrives in the ER, and immediately has an ECG done that indicates atrial flutter with a 1:3 conduction ratio. When should this patient receive cardioversion to treat this condition? A.Immediately upon arrival to the ER B.At the same time he receives his medication C.Once the medication has slowed down the arrhythmia D.After admission to the ICU

47. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Premature Ventricular Contractions (PVCs) Occurs when ectopic beats originate in ventricles PVCs are commonly result of hypoxia, electrolyte imbalances, & acid-base disorders QRS complex is wide & has no preceding P wave Frequent PVCs call for treatment of underlying cause (lidocaine offers temporary solution in some cases) 47

48. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Premature Ventricular Contractions (cont.) 48

49. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Ventricular Tachycardia (V-tach) Represent run of 3 or more PVCs in a row Easy to recognize as series of wide QRS complexes with no preceding P wave Ventricular rate is usually 100 to 250/min V-tach represents serious arrhythmia often progressing to V-fib if untreated Treatment includes cardioversion & medications 49

50. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Ventricular Tachycardia (cont.) 50

51. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Ventricular Fibrillation (VF) Represents most life-threatening arrhythmia Defined as erratic quivering of ventricular muscle mass Causes cardiac output to drop to zero ECG shows grossly irregular fluctuations with zigzag pattern Treatment includes rapid defibrillation, CPR, oxygen, & antiarrhythmic medications 51

52. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Ventricular Fibrillation (cont.) 52

53. Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. Pulseless Electrical Activity (PEA) Very rare but serious arrhythmia Characterized by ECG pattern that does not generate pulse Generally, does not occurs without precipitating event, such as tension pneumothorax, MI, drug overdose) Treatment involves emergency life support & immediate reversal of cause 53