Introduction to ECGs Terry White RN 1 Discussion

Introduction to ECGs Terry White, RN 1

Discussion Topics n ECG Monitoring Basics n Standardized Methods & Devices n n Components & Measurements of the ECG Complex ECG Analysis 2

ECG Monitoring 3

ECG Monitoring n n Recording of Electrical Activity Uses Bipolar or Unipolar leads The ECG DOES NOT provide a recording or evaluation of Mechanical Activity!!! 4

ECG Monitoring n Bipolar Leads u 1 positive and 1 negative electrode RA always negative F LL always positive F u Traditional limb leads are examples of these Lead I F Lead III F u Provide a view from a vertical plane 5

ECG Monitoring n Unipolar Leads 1 positive electrode u 1 negative “reference point” u F u calculated by using summation of 2 negative leads Augmented Limb Leads a. VR, a. VF, a. VL F vertical plane F u Precordial or Chest Leads V 1 -V 6 F horizontal plane F 6

ECG Monitoring n Einthoven’s Triangle Each lead “looks” from a different perspective u Can determine the direction of electrical impulses u Upright electrical recording indicates electricity flowing towards the + electrode u F positive deflection 7

Standardized Methods & Devices 8

Standardized Methods & Devices n ECG Paper Device Paper Speed Device Calibration Electrode Placement n Variations Do Exist! n n n 9

Standardized Methods & Devices n ECG Graph Paper u Vertical F 1 axis- voltage small box = 1 mm = 0. 1 m. V u Horizontal F 1 axis - time small box = 1 mm = 0. 04 sec. u Every 5 lines (boxes) are bolded u Horizontal axis - 1 and 3 sec marks 10

Standardized Methods & Devices n ECG Paper Examples u Vertical Axis F No. of mm in 10 small boxes? F No. of small boxes in 2 mm? u Horizontal Axis F No. of seconds in 5 small boxes? F No. of small boxes in 0. 2 second? F No. of small boxes in 1 second? 11

Standardized Methods & Devices n Paper Speed & Calibration u Paper Speed - 25 mm/sec standard u Calibration of Voltage is Automatic u Both Speed and voltage calibration can be changed on most devices 12

Standardized Methods & Devices n Electrode Placement u Standardization improves accuracy of comparison ECGs u 3 Lead and 12 Lead Placement are most common u Assure good conduction gel u Prep area with alcohol prep u Avoid Bone F Large muscles or hairy areas F Limb vs. Chest placement F 13

Standardized Methods & Devices n Electrode Placement u Poor F u placement or preparation Often results in artifact Stray energy from other sources can also lead to poor ECG tracings (noise) F 60 cycle interference 14

Components of the ECG 15

Components of the ECG Complex n Components & Their Representation u P, Q , R, S, T Waves u PR Interval u QRS Interval u ST Segment 16

Components of the ECG Complex n P Wave first upward deflection u represents atrial depolarization u usually 0. 10 seconds or less u usually followed by QRS complex u 17

Components of the ECG Complex n QRS Complex u Composition of 3 Waves Q, R & S F represents ventricular depolarization F much variability F u usually < 0. 12 sec 18

Components of the ECG Complex n Q Wave first negative deflection after P wave u depolarization of septum u not always seen u 19

Components of the ECG Complex n R Wave first positive deflection following P or Q waves u subsequent positive deflections are R’, R”, etc u 20

Components of the ECG Complex n S Wave Negative deflection following R wave u subsequent negative deflections are S’, S”, etc u may be part of QS complex u F absent R wave in aberrant conduction 21

Components of the ECG Complex n PR Interval time impulse takes to move through atria and AV node u from beginning of P wave to next deflection on baseline (beginning of QRS complex) u normally 0. 12 - 0. 2 sec u may be shorter with faster rates u 22

Components of the ECG Complex n QRS Interval time impulse takes to depolarize ventricles u from beginning of Q wave to beginning of ST segment u usually < 0. 12 sec u 23

Components of the ECG Complex n J Point point where QRS complex returns to isoelectric line u beginning of ST segment u critical in measuring ST segment elevation u 24

Components of the ECG Complex n ST Segment early repolarization of ventricles u measured from J point to onset of T wave u elevation or depression may indicate abnormality u 25

Components of the ECG Complex n T Wave repolarization of ventricles u concurrent with end of ventricular systole u 26

ECG Analysis 27

ECG Analysis n n n Rate Rhythm/Regularity QRS Complex P Waves Relationships & Measurements 28

ECG Analysis n Ventricular Rate u Triplicate method F 300 -150 -100 -75 -60 -50 u R-R method F divide 300 by # of large squares between consecutive R waves u 6 Second method F multiply # of R waves in a 6 second strip by 10 u Rate meter unreliable!!! 29

ECG Analysis n Rhythm u Measure R-R intervals across strip u Should find regular distance between R waves u Classification F Regular F Irregular • Regularly irregular • Irregularly irregular 30

ECG Analysis n QRS Complex u Narrow F< 0. 12 seconds (3 small boxes) is normal F indicates supraventricular origin (AV node or above) of pacemaker u Wide F> 0. 12 seconds is wide F indicates ventricular or supraventricular w/aberrant conduction 31

ECG Analysis n P Waves u Present? u Do they all look alike? u Regular interval u Upright or inverted in Lead II? F Upright = atria depolarized from top to bottom F Inverted = atria depolarized from bottom to top 32

ECG Analysis n Relationships/Measurements u PR Interval F Constant? F Less u. P than 0. 20 seconds (1 large bx) to QRS Relationship FP wave before, during or after QRS? F 1 P wave for each 1 QRS? F Regular relationship? 33

ECG Analysis n A monitoring lead can tell you: u How often the myocardium is depolarizing u How regular the depolarization is u How long conduction takes in various areas of the heart u The origin of the impulses that are depolarizing the myocardium 34

ECG Analysis n A monitoring lead can not tell you: u Presence or absence of a myocardial infarction u Axis deviation u Chamber enlargement u Right vs. Left bundle branch blocks u Quality of pumping action u Whether the heart is beating!!! 35

ECG Analysis n n An ECG is a diagnostic tool, NOT a treatment No one was ever cured by an ECG!! Treat the PATIENT not the Monitor!!! 36