3-ECG

Question 1

what electrodes measure

Answer 1

flow of current in/out of cell
-will not record anything when no charge is moving so when fully de/polarized

Question 2

ohms law

Answer 2

I = (Va-Vb)/Rab

current = diff b/t mem voltage divided by resistance of gap junctions to flow

current flows towards the pos pole

Question 3

positive deflections

Answer 3

neg pole @ A pos pole @ B so current flow A>B TOWARS pos pole

so Va-Vb is positive bc A depolarizes first then becomes neg bc A will repolarize first

Question 4

negative deflections

Answer 4

current flow/impulse AWAY from positive pole (switch so pos pole @ A and neg @ B)

Vb-Va negative since A still depolarizes first then becomes pos bc A repolarizes

Question 5

flat recording

Answer 5

will show flat/no deflections if pole is not oriented right, if its perpendicular to axis

polarization still happens its just not picked up/captured

Question 6

standard ECG calibrations

Answer 6

chart speed = 25 mm/sec (every line/box is 1 mm^2)

10 mm = 1.0 mV
5 mm = 0.2 sec, 1 mm = 0.04 sec

Y axis = voltage mV
X axis = time msec

Question 7

leads/cameras

Answer 7

1. 6 @ frontal plane- standard bipolar limb leads + augmented unipolar limb leads
2. 6 @ transverse/horizontal plane- chest leads/precordial

Question 8

augmented unipolar limb leads

Answer 8

aVR + aVL + aVF

Question 9

chest leads

Answer 9

V1-6
V7-9 used to examine posterior heart

show ant-post view and R (v1) to L (V6)
-assume leads are left centered unless R sided electrical activity is suspected

Question 10

lead 1

frontal plane

Answer 10

R arm > L arm (+)

Question 11

lead 2

frontal plane

Answer 11

R arm > L foot (+)

Question 12

lead 3

frontal plane

Answer 12

L arm > L foot (+)

Question 13

lead aVR

frontal plane

Answer 13

from lead 3 (L arm > L foot) > R arm

Question 14

lead aVL

frontal plane

Answer 14

lead 2 (R arm-L foot) > L arm

Question 15

lead aVF

frontal plane

Answer 15

lead 1 (R-L arm) > foot

Question 16

V1

chest lead

Answer 16

@4th intercostal space, R sternal border

Question 17

V2

chest lead

Answer 17

@4th intercostal space, L sternal border

Question 18

V4

chest lead

Answer 18

@5th intercostal space, midclavicular line

Question 19

V3

chest lead

Answer 19

b/t V2 and V4

Question 20

V5

chest lead

Answer 20

in line with V4 anterior axillary line

Question 21

V6

chest lead

Answer 21

in line with V4 and 5, mid axillary line

Question 22

recording electric activity

Answer 22

ECG records instantaneous changes in membrane potential in heart cells
-single depolarizing impulse recorded from different angles/electrodes
-only surface tho so will get mem potential changes of large number of cells detected

Question 23

QT interval

Answer 23

ventricular myocyte action potential

Question 24

deflections in ECGs

Answer 24

1. P wave
2. QRS complex
3. T wave

Question 25

intervals of ECGs

Answer 25

1. PR interval 2. ST segment 3. QT interval

Question 26

P wave

Answer 26

summation of atrial myocytes depolarizing, phase 0 of atrial myocytes pos charge towards electrode = upward deflection

Question 27

QRS complex

Answer 27

ventricular depolarization event, phase 0 of vent myocytes Q = slight neg deflect from depolar in septum, any neg before R R = pos deflect from depolar spread toward electrode, down apex, any pos before S S = neg deflect from depolar spread away from electrode, vent free walls, any neg after R can be uppercase (big deflect) or lowercase (small deflect) | L vent takes longer to depolar bc bigger

Question 28

QRS complex

Answer 28

ventricular depolarization event, phase 0 of vent myocytes Q = slight neg deflect from depolar in septum, any neg before R R = pos deflect from depolar spread toward electrode, down apex, any pos before S S = neg deflect from depolar spread away from electrode, vent free walls, any neg after R can be uppercase (big deflect) or lowercase (small deflect) | L vent takes longer to depolar bc bigger

Question 29

T wave

Answer 29

summation of ventricular cells repolarizing, phase 3 - direction same 'concordant' as QRS bc reversal of charge movement, upward

Question 30

T wave concordance

Answer 30

ventricle repolarizes opposite direction than depolarized (reversal of charge) depolar start @endocardium > epicardium repolar start @epicardium > endocardium

Question 31

PR segment

Answer 31

P wave + flat line before QRS = depolar of atria, AV node, bundle His, bundle branches, purkinje aka everything upstream of ventricles

Question 32

QT interval

Answer 32

start at beginning of QRS - ends wherever T wave returns to baseline -AP of vent myocytes

Question 33

ST segment

Answer 33

flat line b/t QRS complex and T wave aka phase 2/plateau vent myocytes -isoelectric so no current detected

Question 34

J point

Answer 34

junction of termination of QRS and ST segment

Question 35

ECG NOT detect

Answer 35

1. SA node 2. Atria 3. AV node 4. bundle His 5. bundle branches 6. purkinje fibers

Question 36

finding heart rate

Answer 36

use R-R interval (but techncially any deflection can be used) -gives time b/t ventricular depolars/contracts | P-P is atrial depolar

Question 37

methods for calculating HR

Answer 37

1. small boxes, (1500 mm/min) / boxes b/t R peaks 2. big boxes, 300/big boxes 3. 3 sec marker, count # QRS in 3 sec x 20 4. 10 sec strip, QRS in 10 sec x 6 | 3 and 4 good for irregular

Question 38

bradycardia

Answer 38

HR < 60 beats/min sinus bradycardia = slow heart beat og @ sinus node -slow diastolic depolar in sinoatrial nodal cells junctional bradycardia = slow heart beat og @ AV junction

Question 39

tachycardia

Answer 39

HR > 100 beats/min sinus tachycardia og @ sinus node -fast diastolic depolar in sinoatrial nodal cells

Question 40

sinus rhythm rules

Answer 40

1. every P wave followed by QRS 2. every QRS preceeded by P wave (bc could have QRS without) 3. P waves move upward increasingly leads I/II/III 4. P wave interval in more than 0.12 sec (>3 small boxes) and not more than 0.2 sec 5. normal rhythm HR b/t 60-100 and meets 1-4 6. sinus bradycardia <60 and meets criteria, sinus tachycardia >100 and meets criteria

Question 41

P wave abnormalities

Answer 41

if R atrial enlargement then P waves tall in I/II/III/AVF if L atrial enlarge then P in II are broad/notched, in V1 are deep/wide -slightly exaggerated in both

Question 42

wide QRS complex

Answer 42

wide = greater than 3 boxes/0.12 sec means depolar does not occur thru specialized conduction system, not regular -vents taking a long time

Question 43

if voltage lower than expected

Answer 43

bc small size heart, fluid interference limb leads under 5 mm precordial/chest leads under 10 mm

Question 44

voltage higher than expected

Answer 44

more muscle mass/cells contributing to deflection, less interference precordial leads good for hypertrophy

Question 45

R wave progression

Answer 45

inc size from V1-6 bc depolar starts to the R then moves L damage to muscle cells or ischemia change movement

Question 46

tissue hypoxia-ST segment

Answer 46

hypoxia dec ATP + act K channels = mem potential inc/less neg dec ATP = dec act of Na/K ATPase

Question 47

infarct - ST segment

Answer 47

mem potential of larger affected area depolars so shift baseline lower -big infarct/areas of tissue damage = ST elevation -small ischemia = ST depression

Question 48

hexaxial coordinate system

Answer 48

I = 0 degrees II = 60 III = 120 aVF = 90 aVR = 210 aVL = -30 | frontal plane

Question 49

how to determine axis

Answer 49

1. look at net direction to find quadrant -lead I = R/L + lead aVF = up/down 2. find most isoelectric (perpendicular) 3. check by looking at 90 (parallel lead)