12 lead ecg

1. 12 Lead ECG
Heidi Whitman, ICP Paramedic

2. Role of the 12 Lead

3. Role of the 12 Lead
•12 Lead ecgs are a diagnostic test that help to
identify pathologic conditions, particularly in
acute coronary syndrome (ACS) and acute
myocardial infarction (AMI)
•Indicated in: arrhythmias, ACS symptoms,
overdoses, strokes, pulmonary emboli
•How many times have we seen an AMI where
SOB is the only presenting symptom?!

4. Early and Often
•Cardiac events are a
changing process
•Obtaining capture of ST
segment elevation is
important because it will
speed time to
thrombolysis once patient
is in the ER
•GTN treatment can mask
the signs of infarction by
reducing elevation

5. •Our goal in EMS is to ensure the best
outcome for our patients
•This means becoming quick and
proficient at performing 12 leads so
that on-scene times still remain
minimal

6. How it works
•The leads record electrical
activity and depolarization
•The waveforms obtained from
each lead vary depending on
the location of the lead in
relation to the wave of
depolarization passing through
the myocardium
•As electricity passes through
the heart, it creates small
electrical forces called vectors.
The mean of all these vectors
is called the axis.

7. A picture of the heart

8. How it works
•Limb leads measure
along the frontal
plane of the heart
•Precordial leads, V1-
V6, measure around
the horizontal plane of
the heart

9. Lead Placement

10. Lead Placement
•Angle of Louis is where the second rib connects to the
sternum
•V1 and V2 are 4
th
intercostal space, on the sternal border
•V4 is midclavicular 5
th
intercostal
•V3 split the difference
•V6 is midaxillary 5
th
intercostal
•V5 split the difference
•V4R is midclavicular on the other side, remember to
mark it on the ecg!
•V7-V9 continue around the chest on the left side, mark it
on the ecg!

11. Lead Placement
•Do a right sided 12 lead when there are
inferior changes and especially when lead
3 changes are greater than lead 2
•Do a posterior 12 lead when there is ST
depression in leads V1 and V2… (more on
reciprocal changes later)

12. Let’s Practice!

13. Axis
•The axis of the heart is the average direction of
the heart’s electrical activity during ventricular
depolarization
•Myopathies can affect the axis and should
increase the medic’s index of suspicion that
something bad is happening
•Causes of left axis deviation (LAD): AMI, LAHB
(fascicle block), LBBB, LVH, WPW, ageing,
mechanical shifts (pregnancy, ascites)
•Causes of right axis deviation (RAD): AMI,
RBBB, emphysema or other respiratory
disorders

14. Axis
•How to determine axis deviation: Look at leads 1
and aVf..
•Are they positive or negative?

15. Waveforms
The PR interval should be no longer than 0.20s, or 5 little squares.
The length of the QRS should be shorter than 0.12s, or 3 little squares.

16. Q waves
•Deep or long q waves
are abnormal and bad
•Abn q waves indicate
that an AMI has
happened in the past
or is happening right
now, but we can’t tell
•Longer than 0.03s
=Bad, or deeper than
1/3 the height of the R
wave =Bad

17. R wave progression
•R waves start in V1 as negative and gradually
progress to positive deflection in V6, with the
change happening in V3-V4
•If R wave progression isn’t smooth, or
doesn’t progress at all, then increase your
index of suspicion that something is Bad!

18. ST segment
•ST changes from
baseline can indicate
bad things for the
heart
•ST depression
indicates ischemia
•ST elevation indicates
injury or infarct
•Also beware the
sloping ST segment

19. ST segment
Gross elevation is often
described as tombstoning, or
a fireman’s hat

20. T waves
•T waves should be rounded and upright,
not tall, peaked or inverted
•Inverted T waves don’t always mean
something is wrong, but they shoud
increase your index of suspicion of
ischemia

21. Blocks
•The heart contains conduction
pathways of specialized cells,
called fascicles, which transmit
electrical impulses throughout
the heart and depolarize the
ventricles.
•Fascicular blocks are different
than those found in
dysrhythmias, as those are
blocks at or around the AV
node
•Bundle branch blocks (BBB’s)
are not diagnoseable on a 3-
lead rhythm strip

22. BBB
•Bundle branches are bundles of fascicles
•If cardiomyopathy occurs in the BB’s then
these specialized cells are unable to
quickly conduct impulses
•Depolarization then occurs through regular
ventricular cells which are much slower to
conduct and stimulate the ventricles =wide
QRS

23. BBB
•If the QRS is 0.12s (3 little boxes) or
longer =BBB
•0.11s does not equal a block!
•Examine lead V1 and V6 to determine
whether it is the right or left side; RBBB vs
LBBB

24. RBBB
•RBBB causes: MI,
CAD, or lung
disorders stressing
the heart such as
corpulmonale or PE,
also rate-related
RBBB
•V1 changes: rabbit
ears, tall R
•V6 changes: slurred s
wave

25. LBBB
•LBBB causes: AMI, CHF,
CAD
•New LBBB=STEMI
•Frequently will require a
pacemaker
•V1 changes: big broad
complex with negative
deflection
•V6 changes: big broad
complex like a PVC

26. BBB
•The turn signal technique for figuring out if its
RBBB or LBBB:
Flick the lever to go Right, it
pops up, like the tall R wave
in an RBBB in V1
Flick the lever to go Left, it
pops down, like the deep
complex in LBBB in V1

27. AMI in BBB’s
•Any new onset LBBB, call a
STEMI
•ST elevation in LBBB is
normal, however ST
elevation of 5mm or more in
an old LBBB =STEMI
•Be suspicious of new RBBB
•There are no ST changes
normally associated with
RBBB so any elevation
=STEMI

28. AMI

29. AMI
•Initial goals of EMS: limit the
size of infarction by decreasing
cardiac workload and
increasing oxygen supply to
the myocardium
•Rest, O2 as needed, ASA,
GTN, iv fluid and pain relief prn
•Long term goals for EMS:
definitive care including
expediting transport to hospital
and decreasing amount of time
to needle (thrombolysis), such
as starting an IV, doing a 12
lead

30. SALLI
S =septal, A =anterior, L =(low) lateral, L =(high) lateral, I =inferior
Memorize this as an aid to locating AMI’s on the heart!

31. Coronary Arteries
•The different areas of the
heart are fed from certain
arteries
•The left ventricle is the
main pump for the body,
which is why an occlusion
in the LAD is called the
widowmaker
•Because one artery can
feed many areas, we
rarely get an AMI isolated
to one area. i.e. an
anteroseptal MI with
lateral extension

32. Reciprocal changes
•Damage to the myocardium
represented by ST elevation
will be reflected as ST
depression on the
anatomically opposite side
•Inferior leads are reciprocal
to high laterals and anterior
leads
•Anterior leads are reciprocal
to posterior leads
•Look at reciprocal leads to
help you confirm elevation

33. Septal MI
Which leads are the septal leads?

34. Anterior MI
What kind of block is this? LBBB or RBBB?

35. Lateral MI
Where else is there involvement? Are there reciprocal changes?

36. Lateral MI
Reciprocal changes? Is this high lateral or low lateral?

37. Inferior MI
Do you think the depression in the precordial leads is reciprocal or ischemic?
Which coronary artery can cause this much damage?

38. Right sided MI
This good medic marked V4R on her 12 lead 
What made this medic suspect right sided involvement?

39. Posterior MI
What made this medic suspect posterior MI?

40. Ya, I feel that way too… don’t worry, we’re almost done!

41. Imposters: Pericarditis
•Pericarditis can cause global ST elevation and PR
interval depression.
•S/S: sharp pn that hurts more leaning forward, hx of
infection

42. Impostors: Early Repolarization
•Early Repolarization is usually benign and symptomless
•It is found in young skinny men
•Note the distinctive notched J-point

43. Impostors: Hypothermia
•Hypothermia will also cause a notched J-point
•Careful moving the hypothermic patient as they
can easily turn into VF from movement

44. Impostors: LVH
•Left Ventricular Hypertrophy is usually caused by a lifetime of hypertension,
so suspect cardiac problems
•LVH can cause ST elevation and depression as a normal variant. Use the
same criteria as LBBB for diagnosing an AMI, 5mm or more of elevation.

45. Impostors: Hyperkalemia
•S/S: vague complaints, syncope, weakness
•Suspect in kidney disorder pts, esp dialysis, also in
adrenal disorders, or secondary to diuretics
•The p-wave will flatten out and the t-waves will become
tall and peaked. Eventually VT/VF likely.

46. Impostors: Digoxin toxicity
•Digoxin is a drug commonly used to treat advanced CHF
•It has a small therapeutic index meaning it is easy to OD
•It can cause a depressed scooping ST segment, in addition to other
cardiotoxic changes.
•Patients with dig tox will describe seeing a “yellow haze”

47. All Done!!
Time to do
Bad things
To our
Arteries!!