Electrocardiogram Flashcards
ECG
Body surface recording of a change in electrical potential which is a projection of the net potential changes occurring in hearth
Horizontal axis ECG
1 mm section, One square equals 0.04 sec
Vertical axis ECG
A 10 mm deflection equals 1 mV
at rest placed as vert midpoint
Isoelectric line
Vert midpoint of paper 0 mv
Upward deflection is +
Downward deflection is -
P-wave
represents atrial depolarization
sum of all phase 0’s in atrial tissue
P-R interval
Amount of time from beginning of P wave to beginning of QRS complex. ). 0.12 to 0.20 sec.
(less embryo kent bundle)
First degree block
PR excessively long
Conduction through AV node is reduced.
All P wave still have a QRS
Second degree block
Not all P waves have a QRS .
Some do not pass through AV node. 1:1
Third degree block
No P waves conduct through AV node complete block
QRS complex
sequential depolarization of the ventricular cells.
Duration 80ms over 120 ms conduction defect R & L block
S-T segment
Long period through phase 2. Non polar plateau
Acute injury and S-T
Phase 2 would be something other than 0
Lack of current flow
OLD INFARCTS don’t show ST shift
T wave
Ventricular depolarization Summation of phase 3’s
U wave
May represent repolarization of the papillary muscles or purkinje conduction system
ECG Phase 0 atrial
P wave
ECG Phase 0 ventricular
QRS complex
ECG Phase 3 ventricular
T wave
Normal duration of PR and QRS
PR 140 ms
QRS 80-120 ms
ECG Unipolar limb leads
AVR, AVL & AVF.
Compare voltage diff btw 1 point and ground
ECG AVR ex
+ lead on R arm, - lead on L arm & L leg.
R lead bisects the angle created by intersection of Leads I and II perpendicular to lead III
ECG bipolar limb leads
Measures diff btw two points on the body.
Equilateral ( Einthoven’s) triangle formed.
Analyzes ECG in frontal plane
Ex RA, LA & LL
Describe the unipolar chest leads
i. V1 – 4th intercostal space, rt sternal border
ii. V2 – 4th intercostal space, lt sternal border
iii. V3 – midway between V2 and V4 on line joining two points
iv. V4 – 5th intercostal space, midclavicular line (left side)
v. V5 – Anterior axillary line same level as V4
vi. V6 – Mid axillary line same level as V4 and V5
b. Analyze ECG in horizontal plane
Formula
HR = 1/n x chart speed
Select 2 points
Count number of large boxes (n)
Counting method
Memory 6 300,150,75, 60 & 50
Division by 300
number of boxes
ex: 300/4 = 75
Marked paper
hospital use paper with intervals in seconds
ex: 3 sec measure six and multiply by 10
Describe the hexaxial reference system in the frontal plane
Utilizes equilateral triangle leads I, II, III & unipolar chest lead
Center point id AV
Axis leads move to intersect AV at midpoint
Augemented voltage lead superimposed to get degree
Normal axis
0 to 90 degree
Right axis deviation
90 to 180 degree
End of deep inspiration
Moving to standing position
Tall stature
Hypertrophy (pulmonary valve stenosis, pulmonary hypertension, congenital malformations)
Right bundle branch block (signal travels faster in normal LV)
Wide QRS
Left axis deviation
0 to - 90 degree
End of deep expiration
Supine posture
Obesity
Hypertrophy (systemic hypertension, valvular disease, congenital)
Left bundle branch block (signal travels faster in normal RV)
Also shows wide QRS
Approximation of mean degree
a. Select any two leads 90 degrees apart from each other (lead I and AVF are convenient because they are horizontal and vertical respectively)
b. Evaluate the QRS in lead I (if deflected in positive direction, vector point to left (positive pole))
c. Evaluate QRS in AVF (if deflection is positive, arrow points down (towards positive pole))
d. Use vector addition to determine the resultant mean axis
