PRACTICAL ELECTROCARDIOGRAPHY

1. PRACTICAL ELECTROCARDIOGRAPHY M. Catherine Hough Ph.D, RN Kathy Robinson RN, Ph.D, CCRN Spring Semester 2002

2. Electrocardiogram EKG or ECG

3. Characteristics of EKG Paper • Horizontal Axis is a function of time • Vertical Axis indicates amplitude ONLY in a calibrated recording

5. Calculating EKG Rate

6. Calculating EKG Rate

7. Components of the QRS Complex

8. P wave • The P wave represents the depolarization of the atria (atrial depolarization) • The P wave contour is usually smooth • entirely positive (Leads I, II, III, aVF, and V4 to V6) • negative (aVR) (monophasic) in all leads except V1

9. P wave • The P wave duration is normally less than 0.12 sec. • The P wave amplitude is normally less than 0.25 mV in all leads • The P wave normally appears entirely upright

10. PR Interval • The PR interval measures the time required for the impulse to travel from the atria myocardium adjacent to the SA node to the ventricular myocardium adjacent to the fibers of the Purkinke network (atrial and ventricular depolarization)

11. PR Interval • The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. • Normal PR interval duration range is from 0.12 sec - 0.20 sec

12. QRS Complex • represents depolarization of the ventricles (ventricular depolarization) • If the first deflection from the isoelectric line is negative it is a Q wave (not always present) • The first positive deflection from the isoelectric line is an R wave • The negative deflection following an R wave is an S wave

13. QRS Complex • Normal QRS interval range is from 0.04 sec - 0.12 sec • Measured from the first deflection from the isoelectric line to the J-point • (J-point is where the QRS complex ends and the ST segment begins)

15. ST Segment • represents the plateau (phase 2) of the action potential (ventricles in active state following depolarization, but NO electrical activity occurs at this time. • Is normally isoelectric - no difference exists in electrical potential among the action potentials of the heart • No current flow occurs because all cells are at zero potential

16. T wave • represents phase 3 of the action potential, when the ventricles are being rapidly repolarized (ventricular repolarization) • Is normally rounded, slightly asymmetric, and the same polarity as the QRS complex • The effective refractory period is present during the beginning of the T wave.

17. QT interval • represents the entire duration of ventricular depolarization and repolarization (ventricular refractory period is the time necessary for the ventricle to depolarize, then repolarize) • The normal QT varies with age, gender, and heart rate

18. Cardiac Rhythms

19. Five Steps to Rhythm Interpretation • Determine the rate • Identify the P Waves • are they present? • How do they relate to the QRS • Identify the QRS Complex • How do they relate to the P Waves? • Measure the P-R interval • Measure the QRS interval

20. Specialized Conduction System of • SA Node (highest rate of automaticity) • Located on POSTERIOR surface of Rt. Atria • Internodal atrial pathways • Anterior Tract (Bachman’s Tract) • Middle Tract (Wenchebach) • Posterior Tract (Thorel’s) • Bachman’s BUNDLE - conducts impulse from SA node to Lt.. Atria • AV NODE • Delays impulses from atria before they go to ventricle • Allows for ventricular filling

21. Intraventricular Conduction System • Bundle of His • RBBB • LBBB • Purkinje System

22. Electrical Activity of the Heart The above is borrowed from the web site: http://www.heartsite.com

23. Cardiac Properties The heart normally possesses four intrinsic functional properties that are the result of electrical activity occurring @ the myocardial cell membrane 1. Automaticity - intrinsic to the pacemaker cells of the heart. These cells have the ability to discharge an electrical impulse automatically without & outside stimulus Inherent rates of automaticity: a. SA node 60-100 bpm b. AV junction 40-60 bpm c. His-Purkinje system 20-40 bpm

24. Cardiac Properties 2. Excitability- refers to the ability of cells to become electrically charged in response to an outside electrical stimulus • The degree of excitability is directly related to how much recovery time the heart has had before the next electrical stimulus is received

25. Cardiac Properties 3. Contractility- refers to the ability of cardiac muscle fibers to shorten or contract in response to an electrical stimulus • This property is scientifically based on the Frank-Starling Law which claims: • “To a point, the longer the muscle fiber is stretched, the greater its force of contraction. If however the muscle fiber is overstretched, the contraction will be weak”

26. Cardiac Properties 4. Conductivity- refers to the propagation of an impulse from cell-to-cell. Achieved by two methods: • Interconnected muscle fibers with intercalated discs • Specialized conduction system

27. SA node

28. Normal Sinus or Regular Sinus Rhythm (NSR or RSR) • P wave present and regular. • Atrial rate (P waves) between 60 and 100 beats/min • Each P wave is followed by a QRS complex

30. Sinus Bradycardia • P wave present and regular • Atrial rate (P waves) < 60 beats/min • Each P wave is followed by a QRS complex • RX: • May require no treatment • Atropine IV • May require temporary pacemaker or permanent pacemaker

32. Sinus Tachycardia • P wave presentand regular • Atrial rate (P waves) > 100 beats/min • Each P wave is followed by a QRS complex • RX: • treat underlying cause

34. Sinus Arrhythmia • P wave present • P-P interval - phasic shortening then lengthening of P-P interval, usually with respirations • Impulse initiation by SA node • RX: • usually none

36. Common Arrhythmias Originating from Atria:

37. Premature Atrial Contractions (PAC) • initiated by ectopic focus in the atria • premature P wave with a contour different from a sinus P wave (location of ectopic focus determines its shape) • QRS may or may not be normal • PAC is followed by a pause ~ equal to the sinus cycle • (measured R to R)

38. Premature Atrial Contractions (PAC) • associated with use of caffeine, stress, or use of tobacco • may be a precursor to developing uncontrolled AF • RX: • may require no treatment • sedation • quinidine

40. Atrial Flutter • rapid sawtooth P waves • ventricular rate regular • associated with CAD, pulmonary embolism, mitral valve disease, and thoracic surgical procedures. • atria depolarize at a rate of 250 to 350 beats/min

41. Atrial Flutter • RX: • cardioversion • digitalis • ibutilide • IV diltiazem

43. Atrial Fibrillation • rapid irregular P waves > 350/min • ventricular rate irregularly irregular • ventricular rate varies, may increase to greater than 150 if untreated • if rate > 100 beats/min referred to as uncontrolled AF • if rate < 100 beats/min referred to as controlled AF

44. Atrial Fibrillation • RX: • digitalis • cardioversion • quinidine • IV dilitiazem

46. Sick Sinus Syndrome (SSS) • term to describe several disorders of the SA node • tachycardia-bradycardia syndrome is the most common type of SSS • complication associated with SSS is CHF and CVA resulting from thromboembolisms • RX: • stabilization of heart with perm pacemaker

48. Atrial Tachycardia • rate 150 to 250 beats/min • P wave present but may be hidden • QRS is generally normal • ventricular rate is regular • RX: • usually none • prolonged episodes may require carotid sinus pressure, vagal stimulation, verapmil, digitalis, or beta blocks

50. Impulse Conduction Deficits A-V Blocks