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 and allow 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 intervention therapy. 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, however the 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 must be 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 num erically consecutive, they are also contiguous. 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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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
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.
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.