##### Medicine: Rapid Interpretation Axis

what does axis refer to

direction of depolarization which spreads throughout the heart to stimulate the muscle fibers to contract

what do we use to demonstrate the direction of electrical activity in the heart

vector

what represents on ECG the electrical stimulation of the ventricles

QRS complex

are ventricular stimulation and contraction coincident

yes (but contraction lasts longer)

how would the ventricular depolarization be shown vectorally on the heart

endocaridum vectors pointing outward

what transmits the electrical impulse from the AV node to the ventricles

BB

would the vectors of one of the sides of the heart be larger if we were monitoring electrical activity

yes left

how does the ventricular septum depolarize

left to right

if we add up all the small vectors of ventricular depolarizaiton, where will the QRS mean vector generally ponit

as the heart does

what is the origin of the mean QRS vector

AV node

what ventricle would the mean QRS vector point toward

left ventricle because it is sllightly larger

how is the mean QRS vector's position noted

in degrees on a circle over the patient's chest

what is the center of the mean QRS vector's circle

AV node

how does the mean QRS vector normally point

downward and to the left between 0 and +90 degrees

if the heart is displaced in a certain direction, where will the mean QRS vector be displaced

in that same direction

in very fat people, the diaphragm is pushed up (on the herat) and so the mean QRS vector may point where

horizontally to the left

what is always the tail of the mean QRS vector

AV node

with hypertrophy of one ventricle, what will happen to the mean QRS vector

greater electrical activity on one side displaces the vector to that side

in myocardial infarction, where will the mean QRS vector be deflected

away from the infarct since it does not conduct electrical activity

when does myocardial infarction occur

when a branch of one of the coronary arteries has become occluded

so in general, where wil the vector ponit in hypertrophy and infarction

hypertrophy twoard, infarction away

what is the positive electrode in lead I

left arm

what is the negative electrode in lead I

right arm

what charge is the right half of the sphere in lead I

negative

what i charge s the left half of the sphere in lead I

positive

what will happen on the ECG as the positive wave of depolarization within herat cells moves toward a positive (skin) electrode

upward deflection

if the QRS complex is positive in lead I, where is the mean QRS vector necessarily pointing

somewhere into the left half (positive half) of the sphere

if the QRS complex is mainly negative in lead I, where is the mean QRS vector necessarily poniting

patient's right side

if the QRS is negative in lead I, what do we call this

right axis deviation (vector toward the right)

where is the positive electrode of aVF

left foot

where is the sphere of consideration for the aVF lead

all around the patient

in the aVF sphere, what is the downward portion of the sphere considered

positive

what is the center of the Avf sphere

AV node

is the upper or lower half of the AVF sphere negative

upper half

in AVF lead if the QRS is mainly positive on the tracing, where does the mean QRS vector ponit

downward

(SO THINK ABOUT THIS: QRS in AVF is POSITIVE, but the vector ponits DOWNWARD)

in AVF if the QRS is negatvie, where does the vector point

upward into the negative half of the sphere

if the QRS is positive in lead I and also in AVF, where does the vector ponit

downward and to patients left (normal)

where are the four classifications of areas where the mean QRS vector can point

right axis deviation (right side)

left axis deviation (left and up)

normal range (down and left)

by finding into which quadrant the vector ponits, what does this tell us

direction in which ventricular polarization is happening

if the QRS is positive in lead I and negative in AVF, where does that place the vector

upper left quadrant

if the vector is poniting upwards, where is the QRS in lead AVF relative to baseline

below

if the vector ponits upward and to the patient's left, what would we call this

left axis deviation

any time the QRS is negative in lead one, what do we call this

right axis deviation

if the QRS is positive in lead I and negative in lead AVF, what will the deviation be

left axis deviation

if the mean QRS vector ponits downward and to the patient's left, would we expect the QRS complexes in leads I and AVF to be positive or negative

postiive

if the QRS complex is negative in lead I and AVF, what would this be called

extreme right axis deveiation

when depolarization proceeds in a direction perpendicular to the orientation of a given lead, what is this deflection referred to as

minimal or isoelectric

in an isoelectric step of conduction, what is true about the positive and negative portions of the QRS complex

they are about equal

although the positive and negative deflections of an isoelectric QRS are equal in magnitude, are they generally big or small

small

after locating the mean QRS vector in a given quadrant what can we do by noting the lead in which the QRS is most isoelectric

be more precise about the vector: it will be about 90 degrees from the orientation of the most isoelectric lead

what is the vector degree measure if AVF is the most isoelectric lead if LAD

0 degrees

if lead II is the most isoelectric lead, what is the vector if LAD

-30 degrees

if AVR is the most isoelectric lead, whta is the vector if LAD

-60 degrees

if lead I is the most isoelectric, what is the vector if LAD

- 90 degrees

if AVF is the most isoelectric lead and it is in the normal range, what is the vector

0 degrees

if lead III is the most isoelectric lead and it is in the normal ragne, what is the vector

+30

if AVL is th emost isoelectric lead and it is in the normal range, what is the vector

+60

if lead I is the most isoelectric lead and it is in the normal range, what is the vector

+90

a patient with a vector in the normal range would have an electrical axis of 30 if which lead were isoelectric

III

in extreme RAD and lead I is most isoelectric what is the vector

-90

in extreme RAD and lead AVL is most isoelectric what is the vector

-120

what is the lead if you are in extreme RAD and the vector is -150

lead III

what is the lead if you are in extreme RAD and the vector is -180

aVF

if you are in RAD and the lead I is most isoelectric what is the vector

90

if you are in RAD and the lead is AVR what is the vector

120

what is the lead if you are in RAD and the vector is 150

lead II

what is the lead if you are in RAD and the vector is AVF

180

how is the axis often recorded

like hands of a clock: longer arrow is QRS, shorter is T wave

how much can the T wave and QRS vectors be separated by to show pathology

60 degrees or more

is the T wave represented as bigger or smaller than the QRS vector

smaller

how is an axis noted in literature if it is 60 degrees

A+60 deg

can the mean QRS vector just ponit right left up and down

no, also front or back

what does the ventricular depolarization proceed relateive to the AV node in terms of the front or back of the patient

forward and backward from the AV node!

how is lead V2 obtained

placing electrode sensor on the chest just over the AV node

is the electrode sensor for lead V2 positive or negative

positive

which half of the V2 sphere is positive

front half

if the QRS in V2 is negative where does the maen QRS vector ponit

backward

if there is a positive QRS tracing of lead V2 what does that mean

mean QRS vector is poniting forward (NOT NORMAL)

where is the thick left ventricle located in the chest

posteriorly (so the vector is drawn posteriorly)

what leads only need be considered to find the mean QRS vector in 3d

lead I

AVF

V2

the mean QRS vector can be located in the flat plane over the patient's chest by checking what leads

I and AVF

if the QRS complex in leads I and AVF is positive, is the mean QRS within the normal range

yes

rotation of the vvector around a central axis is referred to as what

clockwise (posterior) or counterclockwise (anterior)

if we drove an iron bar in a straight line through the SVC to the IVC, could the heart rotate around the bar

yes

which septal leads have a QRS that is just as much positive as it is negative

V3 and V4

when the "transitional zone" QRS moves posteriorly toward leads V5 and V6, what is this called

clockwise rotation

if we see a transitional QRS in leads V1 or V2, what is this called

counterclockwise rotation

when clockwise/counterclockwise rotation is noted, what plane is this in

horizontal

when axis deviation is noted, what plane is this in

frontal plane