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McHENRY WESTERN LAKE COUNTY EMS SYSTEM

MID-WINTER 2011 MANDATORY

CONTINUING EDUCATION

PRIMARY AND PROBATIONARY ALS PROVIDERS

12 – LEAD ECG INTERPRETATION

The purpose of this CE is to provide a quick review of 12 Lead ECG interpretation andallow you to hone your skills by reviewing and interpreting several ECGs. So let’s get

started.

When reviewing a 12 Lead ECG for a patient with suspected Acute Coronary Syndrome,there are three distinct pattern changes we are looking for.

1.  ST segment elevation or new onset of an LBBB

2.  ST segment depression or T-wave inversion

3.  Pathological Q waves

This criteria is used to aid us in screening for patients in need of emergent interventiontherapy.

ST segment elevation is the most significant of the patterns we are looking for. It

represents acute injury. At this time the cells are still viable and salvageable, howeverthe cells will die if the hypoxic state is not quickly alleviated. This is why we focus on

this group with a goal to get them to a cath lab for reperfusion therapy as soon as

possible.

The ST elevation is measure at the J point and must be elevated 1mm or more and mustbe found in at least two anatomically contiguous leads. What are anatomically

contiguous leads? If two lead have the same name (i.e. lateral or inferior) they are

contiguous. Also, in the chest lead, if they are numerically consecutive, they are alsocontiguous. For example V2 is call a septal lead, and V3 and anterior lead, but they are

anatomically contiguous. Remember the ST segment is compared to the TP segment not

the PR segment.

ST depression: Any deviation to the ST segment catches the provider’s eye. However,when ST segment depressions appear, realize that ST segment elevation is more

significant and may also be found. If it is, the ST segment depression is considered

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reciprocal to the elevation, and this clue confirms the diagnosis of myocardial injury.The causes of ST depression are as follows:

⇒  Reciprocal changes to ST elevation

⇒  Ischemia or subendocardial injury

⇒  Certain medications, such as digitalis.

If ST segment depression does not appear to be reciprocal (it occurs without any STelevation), the patient may be experiencing myocardial ischemia or injury to asubendocardial wall, which involves a single layer of the heart muscle. These types are

not triaged for emergent reperfusion therapy as ST segment elevation would be, but are

initially observed and treated.

Inverted T waves: One early sign of an acute coronary syndrome and myocardialischemia is T wave inversion. Because at time, the ST changes may disappear as the area

is reperfused after nitroglycerin, a baseline 12-Lead ECG should be acquired before

administering nitroglycerin. Thus, nitroglycerin can be diagnostic as well as therapeutic,

proving that an acute coronary syndrome exists. The inverted T waves should besymmetrical in two or more related leads. It is important to remember that T waves are

normally inverted in Leads V1 and III.

Pathological Q waves: some injury patterns, if left untreated, may develop infarction

patterns, or pathological Q waves. A pathological Q wave signifies infarction, or death

of the tissue. A q wave is considered pathological if it is more than 0.04 seconds wide, orone third of the R wave height. The combination of a Q wave and ST segment elevation

represents an acute myocardial infarction.

The following are the ECG indicators of infarct (necrosis or death):

⇒  Pathologic Q waves

⇒  Greater than 0.04 sec wide or one-third of R wave height.

⇒  When seen with ST elevation, indicates acute ongoing myocardial infarction.

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Locating the MI

I Lateral 

II Inferior 

III Inferior 

aVR 

aVL Lateral 

V1 Septal 

aVF Inferior 

V2 Septal 

V3 Anterior 

V4 Anterior 

V5 Lateral 

V6 Lateral 

 

Just as we use an organized assessment to look for injures with a trauma patient, we must

use an organized approach when “assessing” a 12-Lead ECG for injuries. This

assessment of a 12-Lead is accomplished by using the phrase “I See All Leads.” Thisphrase can be divided into sections by the first letter of each word, representing the order

of lead groups to look at for the ST changes related to an acute MI:I Inferior Leads II, III, aVF

S Septal Lead V1, V2A Anterior Leads V3, V4L Lateral Leads V5, V6, aVL

This system was developed to establish a starting point for the beginning of a systematicassessment of a 12 Lead. The familiarity of Lead II would always have clinicians

looking there first. Therefore, with Lead II representing the inferior lead group, the other

leads were added in a logical progression around the 12 Lead ECG to develop ISAL. Thephrase also reminds the provider to look at all leads.

When assessing a 12 Lead ECG for evidence of an AMI, start in the inferior leads (II, III,

aVF) looking of evidence of ST segment elevation. If you see the elevation, write itdown. Next, move to the septal lead (V1, V2) again inspecting for ST segment elevation.

If you see it, write it down. Continue first looking at the anterior leads then at the lateral

leads for ST segment elevation. Again leads you see ST elevation in. Then look to see if there are any reciprocal changes.

Reciprocal Changes

Remember that ST depression in the presents of ST elevation is considered reciprocal

changes and can be used to reinforce your field impression of an acute MI. For an

inferior wall MI where you see elevation in lead II, III or aVF, you may see a reciprocal

change of ST depression in Lead I and aVL. For an Anterior wall MI where you seeelevation in V3 and V4, you may see reciprocal changes in Lead II, III or aVF. For a

lateral wall MI where you see elevation in Lead I, aVL, V5 or V6, you may see reciprocalchanges in Lead II, III or aVF.

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McHENRY WESTERN LAKE COUNTY EMS SYSTEM

SPRING 2011 MANDATORY CE

PRIMARY AND PROBATIONARY ALS PROVIDERS

12 LEAD ECG INTERPRETATION

Name: _______________________________________

Please print and include name on each sheet.

Level of Practice:_______________________________

Department: __________________________________

Date: ________________________________________

For each of the ECGs below document your interpretation and rationale for thatinterpretation.

1.

Interpretation:____________________________________________________________

Rationale: _______________________________________________________________

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NAME _______________________________________________

2.

Interpretation:____________________________________________________________Rationale: _______________________________________________________________

3.

Interpretation:____________________________________________________________

Rationale: _______________________________________________________________

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NAME ______________________________________________________ 

6.

Interpretation:____________________________________________________________

Rationale: _______________________________________________________________

7.

Interpretation:____________________________________________________________Rationale: _______________________________________________________________

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NAME ______________________________________________ 

.

terpretation:____________________________________________________________

HIS QUIZ IS MANDATORY FOR ALL PRIMARY AND PROBATIONARY ALS

HE QUIZ CAN BE SENT OR FAXED TO THE EMS OFFICE (FAX NUMBERS:

LWAYS KEEP A COPY OF YOUR QUIZ FOR YOUR PERSONAL FILE. A

8

 

In

Rationale: _______________________________________________________________

TPROVIDERS. TO REMAIN CURRENT WITHIN THE MCHENRY WESTERNLAKE COUNTY EMS SYSTEM, THIS QUIZ MUST BE RECEIVED BY THE

EMS OFFICE NO LATER THAN MONDAY, FEBRUARY 28, 2011.

T815/759-8061 OR 8045.) WHEN FAXING, IT IS YOUR RESPONSIBILITY TOCALL THE EMS OFFICE AT 815/759-8040 TO CONFIRM THE FAX WASRECEIVED.

ALATE FEE OF $25.00 WILL BE CHARGED FOR ANY QUIZZES RECEIVEDAFTER MIDNIGHT, FEBRUARY 28, 2011.