12 Lead ECG Interpretation: Color Coding for MI’s

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Objectives  review the ECG waveform and intervals Define myocardial ischemia, injury and infarction  Identify the 5 major infarct areas on the 12 lead  Name occluded arteries common to the area Differentiate ECG changes reflecting ischemia, injury and infarction  Identify cardiac enzymes associated with ACS ©2004 Anna Story 2

The 12-Lead view  Each limb lead I, II, III, AVR, AVL, AVF records from a different angle  Al six limb leads intersect and visualize a frontal plane  The six chest leads (precordial) V1, V2, V3, V4, V5, V6 view the body in the horizontal plane to the AV node  The 12 lead ECG forms a camera view from 12 angles ©2004 Anna Story 4

Precordial lead snapshots  Think of each precordial lead as a horizontal view of the heart at the AV node  With the limb leads and the precordial leads you have a snapshot of heart portions ©2004 Anna Story 6

Unipolar and Bipolar  Limb leads I, II, III are bipolar and have a negative and positive pole  Electrical potential differences are measured between the poles  AVR, AVL and AVF are unipolar  No negative lead The heart is the negative pole Electrical potential difference is measured betweeen the lead and the heart  Chest leads are unipolar  The heart also is the negative pole ©2004 Anna Story 7

Lead Placement is Important  Each positive electrode acts as a camera looking at the heart  Ten leads attached for twelve lead diagnostics. The monitor combines 2 leads.  Mnemonic for limb leads  White on right  Smoke(black) over fire(red)  Snow(white) on grass(green) ©2004 Anna Story 8

The ECG Tracing: Waves  P- wave  Marks the beginning of the cardiac cycle and measures the electrical impulse that causes atrial depolarization and mechanical contraction  QRS- Complex  Measures the impulse that causes ventricular depolarization  Q-wave- may or may not be evident on the ECG  R-wave- first upward deflection fol owing P wave  S-wave- the first downward deflection fol owing the R- wave  T- wave  Marks ventricular repolarization that ends the ©2004 Anna Story 11 cardiac cycle

Intervals and Segments  P-R interval-  Time interval for impulse to go from the SA to the AV node  normal 0.12-0.20 secs  QRS Interval  Time interval for impulse to go from AV node to stimulate Purkinjie fibers  Less than 0.12 secs  QT Interval  Time interval from beginning of depolarization to the end of repolarization  Should not exceed ½ the length of the R-R  ST segment  end of the S to the beginning of the T ©2004 Anna Story 12

ECG Changes: Injury  ST segment elevation of greater than 1mm in at least 2 contiguous leads  Heightened or peaked T waves  Directly related to portions of myocardium rendered electrical y inactive Baseline ©2004 Anna Story 15

ECG Changes: Infarct  Significant Q-wave where none previously existed  Why?  Impulse traveling away from the positive lead  Necrotic tissue is electrical y dead  No Q-wave in Subendocardial infarcts  Why?  Not ful thickness dead tissue  But wil see a ST depression  Often a precursor to ful thickness MI  Criteria  Depth of Q wave should be 25% the height of the R wave  Width of Q wave is 0.04 secs  Diminished height of the R wave ©2004 Anna Story 16

Dissecting the 12 Lead ECG  Horizontal marks time Vertical marks amplitude 6 limb leads 6 precordial leads Positioning measures 12 perspectives or views of the heart  The 12 perspectives are arranged in vertical columns  Limb leads are I, II, III, AVR, AVL, AVF Precordial leads are V1, V2, V3, V4, V5, V6 ©2004 Anna Story 18

Color Coding ECG’s Anterior  Yel ow indicates V1, V2, V3, V4  Anterior infarct with ST elevation  Left Anterior Descending Artery (LAD)  V1 and V2 may also indicate septal involvement which extends from front to the back of the heart along the septum  Left bundle branch block  Right bundle branch block  2nd Degree Type2  Complete Heart Block ©2004 Anna Story 21

Color Coding ECG- Inferior  Blue indicates leads II, III, AVF  Inferior Infarct with ST elevations  Right Coronary Artery (RCA)  1st degree Heart Block  2nd degree Type 1, 2  3rd degree Block  N/V common, Brady ©2004 Anna Story 23

As an aside….  Right sided EKG  Ever heard of it?  Ever done one?  Think about it…..  For your cases that are clearly inferior MI’s  Obtain a dextrocardiogram whenever ST segment elevation is noted in Inferior leads ©2004 Anna Story 25

Right Sided EKG????  RVI occurs around 40% in inferior MI’s  Significance  Larger area of infarct  Both ventricles  Different treatment  Right leads “look” directly at Right Ventricle and can show ST elevations in leads II. III. AVF, V4R , V5R and V6R  Occlusion in RCA and proximal enough to involve The single most accurate the RV tool used in measuring RVI. 90% sensitive and specific ©2004 Anna Story 26

Color Coding ECG- Posterior  Green indicates leads V1, V2  Posterior Infarct with ST Depressions and/ tall R wave  RCA and/or LCX Artery  Understand Reciprocal changes  The posterior aspect of the heart is viewed as a mirror image and therefore depressions versus elevations indicate MI  Rarely by itself usually in combo ©2004 Anna Story 30

Color Coding ECG- SubEndo  No color for SubEndocardial infarcts since they are not transmural  Look for diffuse or localized changes and non – Q wave abnormalities  T-wave inversions  ST segment depression ©2004 Anna Story 32

Cardiac Enzymes Indicating Infarct  Normals  CPK- 10-155u/liter  begin rise 3-6 hours and peaks 12-24 with return to norm 3-5 days  CPK-MB < than 5% IU/liter  LDH 85-200 IU/liter  Begin rise 12 hours, peaks 36-72 and normal around 10 days  LDH 1- 18.1% – 29% of total  LDH 2- 27.4% to 37.5% of total ©2004 Anna Story 58

Cardiac Enzymes Indicating Infarct  Troponins- Now the Gold Standard!  Rises after 3-6 hours Negative Troponin within 6 hours of onset of S&S rules out the MI  Peaks at about 20 hours  May be raised for 14 days ©2004 Anna Story 59

Cardiac Enzymes Indicating Infarct  Troponin T  84% sensitivity for MI 8 hours after onset of symptoms  22% for unstable angina  Advantages  Highly sensitive for detecting myocardial ischemia Levels may help to stratify risks  Disadvantages  Less specific than Troponin I Increased in angina Increased in chronic renal failure ©2004 Anna Story 60

Cardiac Enzymes Indicating Infarct  Troponin I  90% sensitivity for MI 8 hours after onset of S&S and 95% specificity  Level greater than 1.2 suggest MI Negative rules out MI Obtain two negative troponin values 4 hours apart Normal y exceedingly low  Even a small elevation indicates myocardial damage ©2004 Anna Story 61

References  Twelve Lead Electrocardiography for ACLS Providers, D. Bruce Foster, D.O. W.B. Saunders Company  Rapid Interpretation of EKG’s , Dale Dubin, M.D., Cover Publishing Co. 1998  ECG’s Made Easy, Barbara Aehlert, RN, Mosby, 1995  The 12 Lead ECG in Acute Myocardial Infarction, Tim Phalen, Mosby, 1996  Color Coding EKG’s , Tim Carrick, RN, H &H Publishing, 1994  www.ecglibrary.com/ecghome.html  www.urbanhealth.udmercy.edu/ekg/read.html  www.ecglibrary.com/ecghome.html  www.nyerrn.com/h/ekg.htm  Drawings by Jill Gregory, Medical Illustrator, CGEY ©2004 Anna Story 62