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Flashcards in EKG Deck (55)
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1

What is normal pathway of conduciton in heart?

  • SA node
    • 60-100 bpm
  • AV node
    • delays conduction for ventircular filing; intiiates impulse 40-60 bpm
  • Bundle of His
    • directs impulse to left/right bundle branches
  • Purkinje fibers
    • reaches into myocardium to stimulate ventricular depolarizaiton/contraction. initiates impulse 20-40bpm

net direction of action potential is from base to apex. heart depolarizes in to out, bottom to top

2

What are the two main vectors in EKG?

vector of depolarization and vectors of repolarization

3

What is the vector of depolarization?

  • QRS complex
  • heart depolarizes from base to apex and endocardium to epicardium
  • myocytes go from internally negative to internally positive--> produces a positive electrical current

4

What is a lead?

  • electrical view of heart
  • each lead represents a view of the heart from a different position
  • each lead of the EKG has two poles; a negative pole and positive pole
    • identify these poles with electrodes on skin
  • Standard limb leads are I, II, III

5

What is lead I

  • Lead I
    • goes from negative electrode on right upper limb to positive elctrode on left upper limb
    • corresponds to view of lateral wall of heart and areas supplied by circumflex artery

6

What is Lead II?

 

  • goes from negative elecrode on right upper limb to positive electrode on left lower limb
  • corresponds to view of inferior wall of the heart and areas supplied by the RCA

7

What is lead III?

  • goes from negative electrod on left upper limb to positive electrode on left lower limb
  • corresponds to view of inferior wall of heart and the reas supplied by the right coronary artery

8

What are the augmented limb leads?

  • Unipolar, meaning they have one positive pole and a reference point in the opposite side of the heart, but use same electrode placement as the standard limb leads
    • referred to as augmented because the voltage must be amplified by the EKG machine
  •  

9

What is aVR?

aVR: right arm electrode is positive and the left arm and left leg electrodes are channeled together to form a common reference point that has a negative charge

10

What is aVL?

  •  left arm electrode is positive 
  • the right arm and left leg electrodes are channeled together to form a common reference point htat has a negative charge
  • corresponds to a view of the lateral wall and areas supplied by the circumflex artery

11

What is aVF?

  • left foot electrode is positive 
  • right arm and left arm electrodes are channeled together to form a common reference point that has a negative charge
  • corresponds to a view of the inferior wall of the heart and areas supplied by the right coronary artery

12

What are the precordial leads?

  • Precordial leads are the last six leads of the EKG and look at events in the heart on a horinzontal plane
    • they view the anterior and lateral surfaces of the heart. 
    • the positive poles are on the anterior and lateral chest and the negative poles are on the opposite side of the positive pole

13

V1?

  • Positive electrode placed directly over right atrium
  • corresponds to the septal wall and areas supplied by the left anterior descending (LAD) artery

14

V2?

  • Positive elctrode placed just anterior to AV node
  • corresponds to septal wall and areas supplied by LAD

15

v3?

  • Positive electrode placed over ventricular septum
  • corresponds to anterior wall of heart and areas supplied by LAD

16

v4?

  • Positive electrode placed over ventricular septum
  • corresponds to anterior wall of heart and areas supplied by LAD

17

V5 and V6?

  • Positive electrodes placed over the lateral surface of the left ventricle
  • corresponds to lateral wall of heart and areas supplied by circumflex artery

18

What is the 5-lead EKG setup?

  • most common system used in operating room
  • takes standard three lead system (right limb electrode, left limb electrode and left leg electrode) and adds right leg and chest electrode
    • by adding the right leg lead electrode, any of the six limb leads can be viewed (I, II, III, avR, avL, avF)
    • the chest electrode can be moved to any of the precordial V positions to obtain all six precordial views (V1-V6)

19

When does a positive deflection occur on the EKG during depolarization?

When vector of depolarization travels towards a positive electrode

ex- lead I

20

When do you get a negative deflection on EKG during depolarization?

  • When vector of depolarization travels away from a positive electrode
  • EX- avR

21

When does biphasic deflection occur on EKG?

When depolarization travels perpendicular to positive electrode

ex- V3

22

How does the heart depolarize?

base to apex and endocardium to epicardium

myocytes go from internally negative to internally positive--> produces a positive electrical current

23

What is the vector of repolarization?

  • T wave
  • Heart repolarizes from apex to base and epicardium to endocardium
  • myocytes go from internally positive to internally negative--> produces a negative electrical current
    • positive deflection occurs when the wave travels away from a positive electrode
  • backwards of depolarization
  • cheat if this is confusing: T wave should always match P wave!!!!

24

What is each small box on EKG worth? Large box?

small= 0.04 sec time; vertical=  1 mm or 0.1 mV

5 boxes= 0.2 sec; vertically= 5 mm or 0.5 mV

5 "large" boxes = 1 second

25

When do you expect to see change in voltage?

When heart contracts more forcefully or when patient has hypertrophy, voltage will be increased

if heart is contracting less forcefully (as seen is tamponade) the voltage will be decreased

26

What is the p-wave?

  • Represents the firing of the SA node and atrial depolarization
  • normally upright in lead II
  • inverted P waves in lead II indicate that conduciton throught he atria occured in retrograde manner--> usually this means the impulse originated in the AV node
    • normal- 1 P wave before every QRS complex, duraiton 0.08-0.12 seconds

 

27

What is the PR interval?

  • beginning of the P wave to beginning of QRS
  • represents the delay of electrical impulse at the AV node to allow for atrial contraction
    • normal 0.12-0.2 seconds

28

What is QRS complex?

  • Represent ventricular depolarization
  • if duration is increased may consider WPW, LVH, BBB
    • normal <0.12 seconds with progressiv eincreased amplitude in V1-V6

29

What is the Q wave?

  • may or mya not be present
  • consider abnormal and possible sign of an MI if amplitude is
    • 1/3 of R wave or
    • duration is >0.04 sec and  depth >1mm
  • Normal <0.04 seconds

30

What is ST segment?

  • follows QRS complex and connects to the T wave and represents ventircular repolarization
  • if ST segment is elevated or depressed by >1 mm, may indicate MI
    • normal= isoelectric