Download Review of Cardiac Anatomy

Nursing 259
12 Lead EKG
Electrical Axis Determination
12 Lead EKG
Graphic recording of the electrical
potentials associated with the heartbeat
 Electrical currents flow in different
directions so different views preferable
 Each lead looks at different area of heart –
overall looks in frontal and vertical planes
 Must be interpreted with client history,
physical assessment and lab data

Clinical Value of EKG
 Myocardial
ischemia and infarction
 Cardiac conduction disturbances
 Arrhythmias
 Cardiac chamber enlargement
 Pericarditis
 Pulmonary hypertension
 Effects of cardiac drugs
 Electrolyte disturbances
Practical Points
Effective contact between skin and
electrodes is essential; use electrode jelly
 Proper grounding of machine and patient is
necessary to prevent AC interference
 Other electrical equipment in contact with
patient may produce artifact
 Patient should be in supine position with
arms at side of body

Pathway of Conduction
 SA node
transmits impulse anteriorly
and inferiorly to AV node
 Simultaneously conducted to L atrium
 AV node to bundle of His
 Septum activated from left to right
 Simultaneously to ventricles - travels
more quickly over right ventricle as it
is thinner; left is thicker
Sequence of Activation
Conduction Pathway
 Since
LV has larger muscle mass, mean
QRS vector is down and to left
 If impulse is traveling towards the
positive electrode, a positive complex
is recorded in that lead
Conduction Pathway
 If
impulse is traveling away from the
positive electrode ; a negative complex
is recorded in that lead
 If impulse is traveling perpendicularly
to the positive electrode a very small or
biphasic complex will be recorded in
that lead
Mean QRS Vector
Conduction Pathway
Planes of Recording
Bipolar Limb Leads
 Records
electrical potentials in the
frontal plane between 2 poles: 1
positive and 1 negative
 + electrode is recording electrode
 Lead I: RA (-); LA (+)
 Lead II: RA (-); LL (+)
 Lead III: LA (-); LL (+)
Bipolar Limb Leads
Unipolar Limb Leads
 Designated
limb is + electrode in
relation to center of heart which is
neutral; also in frontal plane
 AVR - RA (+)
 AVL - LA (+)
 AVF - LL (+)
Unipolar Limb Leads
Unipolar Precordial Leads
 Horizontal
view of electrical activity
 + electrode is electrode moved about
on chest wall
 Leads V1-V6
 Placement of precordial leads should
be precise since QRS morphology and
amplitude can change if inaccurate
Precordial Leads
V1 - 4th ICS - right sternal border
 V2 - 4th ICS - left sternal border
 V3 - midway between V2 and V4
 V4 - 5th ICS - L midclavicular line
 V5 - 5th ICS - L anterior axillary line
 V6 - 5th ICS - L midaxillary line

Precordial Leads
Precordial Lead Views
V1 and V2 are septal leads
 V2, V3 and V4 are anterior leads
 V4, V5 and V6 are lateral precordial leads

Precordial Lead Views
R wave progression
 V1
over right ventricle - impulse will
travel towards electrode and then away
- normal small R wave
 V6 over left ventricle - impulse first
travels away from electrode and then
towards it - normally small Q wave and
large R wave
R wave progression
 Between
V1 and V6 is transitional
zone - R wave should progressively
increase across V leads - called R wave
progression
 Poor R wave progression is suggestive
of anterior wall MI since precordial
impulse flow is interrupted
R wave progression
Right Precordial EKG
Used in dextrocardia and right ventricular
infarctions
 V1 and V2 - same site
 V3R - halfway between V1 and V4R
 V4R - 5th ICS - right midclavicular line
 V5R - 5th ICS - right anterior axillary line
 V6R - 5th ICS - right mid- axillary line

Right Precordial EKG
Electrical axis
Orientation of heart’s electrical activity in
frontal plane
 Review: depolarization of ventricle : first
septum from left to right, then right
ventricle, then left ventricle
 Mean QRS vector is down and to left
 Positive complex, negative complex and
biphasic complex

Electrical axis
Hexaxial reference system: 6 limb leads
intersecting at common center point
 Numerical designations are given to positive
and negative poles of each lead
 Each lead divides the circle by 30 degrees
 The upper half of the circle is negative and
the bottom half is positive
 Divide the circle into quadrants

Normal electrical axis
Down and to left
 From 0 to +90 (can vary from -30 to +110)
 QRS should be predominantly positive in
Leads I and AVF - quadrant method
 For normal axis: impulse must travel in
normal manner, normal muscle mass must
be maintained and all myocardium must be
able to conduct impulse

Normal Axis
Left Axis deviation
From -30 to -90
 QRS: positive in Lead I & negative in AVF
 Causes:

 Left
atrial or ventricular hypertrophy
 Left bundle branch block
 Inferior wall MI
 Pregnancy
 Obesity
Left axis deviation
Right axis deviation
From +110 to +180
 QRS: positive in AVF - negative in Lead I
 Causes:

 Right
ventricular hypertrophy
 Anterior MI
 Pulmonary disease
 Thin person
 Congenital heart disease
Right axis deviation
Indeterminate axis
- 90 to 180
 Extreme right or left

Indeterminate axis
Perpendicular method
More accurate than quadrant method
 First do quadrant method
 Then look for smallest or most biphasic
complex - the axis is perpendicular to this
lead
 Look at right angle to that lead to obtain
numerical value

Normal axis
QRS positive in I and AVF
 Answer is between 0 - +90
 AVL smallest QRS
 Lead II is perpendicular to
AVL
 Axis is +60

Left axis deviation
QRS + in I, - in AVF
 Answer is between 0 and -90
 Most biphasic is AVR
 Lead III is perpendicular to
AVR
 Axis is -60

Right axis deviation
QRS – in I, + in AVF
 Answer is between +90 to 180
 AVF and II are most biphasic
 Leads I, AVL are perpendicular
 Axis is between +150 - +180
 Axis is +165
 That’s a hard one!

Indeterminate axis
All leads are biphasic
 Cannot determine!
