12 Lead ECG

Heidi Whitman, ICP Paramedic

Role of the 12 Lead

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?!

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

• 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

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.

A picture of the heart

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

Lead Placement

Lead Placement

• Angle of Louis is where the second rib connects to the sternum

• V1 and V2 are 4th intercostal space, on the sternal border• V4 is midclavicular 5th intercostal• V3 split the difference• V6 is midaxillary 5th 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!

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)

Let’s Practice!

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

Axis

• How to determine axis deviation: Look at leads 1 and aVf..

• Are they positive or negative?

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.

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

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!

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

ST segment

Gross elevation is often described as tombstoning, or a fireman’s hat

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

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

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

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

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

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

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

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

AMI

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

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!

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

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

Septal MI

Which leads are the septal leads?

Anterior MI

What kind of block is this? LBBB or RBBB?

Lateral MI

Where else is there involvement? Are there reciprocal changes?

Lateral MI

Reciprocal changes? Is this high lateral or low lateral?

Inferior MI

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

Right sided MI

This good medic marked V4R on her 12 lead What made this medic suspect right sided involvement?

Posterior MI

What made this medic suspect posterior MI?

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

Imposters: Pericarditis

• Pericarditis can cause global ST elevation and PR interval depression.

• S/S: sharp pn that hurts more leaning forward, hx of infection

Impostors: Early Repolarization

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

Impostors: Hypothermia

• Hypothermia will also cause a notched J-point• Careful moving the hypothermic patient as they

can easily turn into VF from movement

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.

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.

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”

All Done!!Time to do Bad things To ourArteries!!