3-ECG Flashcards
what electrodes measure
flow of current in/out of cell
-will not record anything when no charge is moving so when fully de/polarized
ohms law
I = (Va-Vb)/Rab
current = diff b/t mem voltage divided by resistance of gap junctions to flow
current flows towards the pos pole
positive deflections
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
negative deflections
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
flat recording
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
standard ECG calibrations
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
leads/cameras
- 6 @ frontal plane- standard bipolar limb leads + augmented unipolar limb leads
- 6 @ transverse/horizontal plane- chest leads/precordial
augmented unipolar limb leads
aVR + aVL + aVF
chest leads
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
lead 1
frontal plane
R arm > L arm (+)
lead 2
frontal plane
R arm > L foot (+)
lead 3
frontal plane
L arm > L foot (+)
lead aVR
frontal plane
from lead 3 (L arm > L foot) > R arm
lead aVL
frontal plane
lead 2 (R arm-L foot) > L arm
lead aVF
frontal plane
lead 1 (R-L arm) > foot
V1
chest lead
@4th intercostal space, R sternal border
V2
chest lead
@4th intercostal space, L sternal border
V4
chest lead
@5th intercostal space, midclavicular line
V3
chest lead
b/t V2 and V4
V5
chest lead
in line with V4 anterior axillary line
V6
chest lead
in line with V4 and 5, mid axillary line
recording electric activity
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
QT interval
ventricular myocyte action potential
deflections in ECGs
- P wave
- QRS complex
- T wave
intervals of ECGs
- PR interval
- ST segment
- QT interval
P wave
summation of atrial myocytes depolarizing, phase 0 of atrial myocytes
pos charge towards electrode = upward deflection
QRS complex
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
QRS complex
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
T wave
summation of ventricular cells repolarizing, phase 3
- direction same ‘concordant’ as QRS bc reversal of charge movement, upward
T wave concordance
ventricle repolarizes opposite direction than depolarized (reversal of charge)
depolar start @endocardium > epicardium
repolar start @epicardium > endocardium
PR segment
P wave + flat line before QRS
= depolar of atria, AV node, bundle His, bundle branches, purkinje aka everything upstream of ventricles
QT interval
start at beginning of QRS - ends wherever T wave returns to baseline
-AP of vent myocytes
ST segment
flat line b/t QRS complex and T wave aka phase 2/plateau vent myocytes
-isoelectric so no current detected
J point
junction of termination of QRS and ST segment
ECG NOT detect
- SA node
- Atria
- AV node
- bundle His
- bundle branches
- purkinje fibers
finding heart rate
use R-R interval (but techncially any deflection can be used)
-gives time b/t ventricular depolars/contracts
P-P is atrial depolar
methods for calculating HR
- small boxes, (1500 mm/min) / boxes b/t R peaks
- big boxes, 300/big boxes
- 3 sec marker, count # QRS in 3 sec x 20
- 10 sec strip, QRS in 10 sec x 6
3 and 4 good for irregular
bradycardia
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
tachycardia
HR > 100 beats/min
sinus tachycardia og @ sinus node
-fast diastolic depolar in sinoatrial nodal cells
sinus rhythm rules
- every P wave followed by QRS
- every QRS preceeded by P wave (bc could have QRS without)
- P waves move upward increasingly leads I/II/III
- P wave interval in more than 0.12 sec (>3 small boxes) and not more than 0.2 sec
- normal rhythm HR b/t 60-100 and meets 1-4
- sinus bradycardia <60 and meets criteria, sinus tachycardia >100 and meets criteria
P wave abnormalities
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
wide QRS complex
wide = greater than 3 boxes/0.12 sec
means depolar does not occur thru specialized conduction system, not regular
-vents taking a long time
if voltage lower than expected
bc small size heart, fluid interference
limb leads under 5 mm
precordial/chest leads under 10 mm
voltage higher than expected
more muscle mass/cells contributing to deflection, less interference
precordial leads good for hypertrophy
R wave progression
inc size from V1-6 bc depolar starts to the R then moves L
damage to muscle cells or ischemia change movement
tissue hypoxia-ST segment
hypoxia dec ATP + act K channels = mem potential inc/less neg
dec ATP = dec act of Na/K ATPase
infarct - ST segment
mem potential of larger affected area depolars so shift baseline lower
-big infarct/areas of tissue damage = ST elevation
-small ischemia = ST depression
hexaxial coordinate system
I = 0 degrees
II = 60
III = 120
aVF = 90
aVR = 210
aVL = -30
frontal plane
how to determine axis
- look at net direction to find quadrant
-lead I = R/L + lead aVF = up/down - find most isoelectric (perpendicular)
- check by looking at 90 (parallel lead)
