The 12 Lead ECG

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Re: The 12 Lead ECG

مشاركةبواسطة دكتور كمال سيد » الأربعاء أكتوبر 31, 2018 8:24 pm

Diagnosis of myocardial infarction

The diagnosis of acute myocardial infarction is not only based on the ECG.
A myocardial infarction is defined as:

Elevated blood levels of cardiac enzymes (CKMB or Troponin T) AND
One of the following criteria are met:
The patient has typical complaints,
The ECG shows ST elevation or depression.
pathological Q waves develop on the ECG
A coronary intervention had been performed (such as stent placement)

So detection of elevated serum cardiac enzymes is more important than ECG changes. However, the cardiac enzymes can only be detected in the serum 5-7 hours after the onset of the myocardial infarction. So, especially in the first few hours after the myocardial infarction, the ECG can be crucial.

ECG Manifestations of Acute Myocardial Ischaemia (in Absence of LVH and LBBB)are :

1- ST elevation
New ST elevation at the J-point in two contiguous leads with the cut-off points : ≥0.2 mV in men or ≥ 0.15 mV in women in leads V2–V3 and/or ≥ 0.1 mV in other leads.
2- ST depression and T-wave changes.
New horizontal or down-sloping ST depression >0.05 mV in two contiguous leads; and/or T inversion ≥0.1 mVin two contiguous leads with prominent R-wave or R/S ratio ≥ 1

A study using MRI to diagnose myocardial infarction has shown that more emphasis on ST segment depression could greatly improve the yield of the ECG in the diagnosis of myocardial infarction (sensitivity increase from 50% to 84%).

Myocardial infarction diagnosis in left or right bundle branch block can be difficult, but it is explained in these seperate chapters:

MI diagnosis in left bundle branch block or paced rhytm ... ced_rhythm
MI Diagnosis in RBBB ... is_in_RBBB

ST elevation is measured at the junctional or J-point


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Re: The 12 Lead ECG

مشاركةبواسطة دكتور كمال سيد » الأربعاء أكتوبر 31, 2018 10:29 pm

The location of the infarct

The heartmuscle itself is very limited in its capacity to extract oxygen in the blood that is being pumped. Only the inner layers (the endocardium) profit from this oxygenrich blood.
The outer layers of the heart (the epicardium) are dependent on the coronary arteries for the supply of oxygen and nutrients.
With aid of an ECG, the occluded coronary can be identified. This is valuable information for the clinician, because treatment and complications of for instance an anterior wall infarction is different than those of an inferior wall infarction.
The anterior wall performs the main pump function, and decay of the function of this wall will lead to
decrease of bloodpressure *
increase of heartrate *
shock *
and on a longer term :* heart failure
An inferior wall infarction is often accompanied with
a * decrease in heartrate because of involvement of the sinusnode.
Longterm effects of an inferior wall infarction are usually less severe than those of an anterior wall infarction.

The heart is supplied of oxygen and nutrients by the right and left coronary arteries.
The left coronary artery (the Left Main or LM) divides itself in the * left anterior descending artery (LAD) and the *ramus circumflexus (RCX).
The right coronary artery (RCA) connects to the ramus descendens posterior (RDP).
With 20% of the normal population the RDP is supplied by the RCX. This called left dominance.

Below you can find several different types of myocardial infarcation. Click on the specific infarct location to see examples.
# Anterior MI (LAD) = ST elevation in V1 - V6

# Septal MI (LAD-septal branches) = ST elevation in V1-V4, disappearance of septum Q in leads V5,V6
QS in V1 and V2. Later the septum-Q in V5 and V6 disappears. Encomprises the ventricular septum which is supplied of blood by the septal branches of the LAD.

# Lateral MI ( LCX or MO ) = ST elevation in I, aVL, V5, V6 + Reciprocal ST depression in II,III, aVF
ST elevation in I, aVL, V5 and V6
Encomprises the lateral side of the left ventricle. This is supplied with blood by the RCX or the MO. The MO, the marginalis obtusis is a sidebranch between the LAD and the RCX. In case of a lateral infarct, the maximal ST elevation is in lead V7 and the maximal depression in V2.

# Inferior MI ( RCA (80%) or RCX (20%) = ST elevation in II, III, aVF + Reciprocal ST depression in I, aVL
ST elevation or depression in V4R can help in differentiating a RCA from a RCX occlusion.

ST elevation in II, III and aVF
This part of the heart muscle lies on the diaphragm and is supplied of blood bij the right coronary artery (RCA) in 80% of patients. In the remaing 20% the inferior wall is supplied by the ramus circumflexus(RCX).
An occlusion of the RCA can be distinguished of a RCX occulusion on the ECG:

Distal RCA occlusion (sens 90%, spec 71%)
*ST segment elevation in III higher than ST segment elevation in II ("the highest elevation points at the culprit")and
ST segment depression in I, AVL, or both (>1 mm)*

Proximal RCA occlusion (sens 79%, spec 100%)
Additional ST segment elevation in V1, V4R or both

RCX occlusion (sens 83%, spec 96%)
ST segment elevation in I, AVL, V5, and V6 and*
*ST segment depression in V1, V2, and V3

# Posterior MI ( RCX = ST elevation in V7, V8, V9 + Reciprocal ST depression in high R in V1-V3 with ST depression V1-V3 > 2mm (mirror view)
High R-waves with ST-depression in V1-V3.
The posterior wall is usually supplied of blood by the RCA. Because no leads "look" at the posterior wall in the normal ECG, no leads show ST-elevation in case of a posterior wall infarction. The ST depressions in V1-V3 that can be observed in case of a posterior wall infarction are in fact mirrored ST elevations and the high R-waves are the Q-waves of the infarct. To be able to confirm a posterior-infarct, leads V7, V8 and V9 may be helpful. These leads are horizontally placed from V6 to the back and do show the ST elevations of the posterior wall.

# (Right Ventricle MI (RCA = ST elevation in V1, V4R + Reciprocal ST depression in I, aVL
Criteria for Right Ventricular MI
ST-elevation >1 mm in lead V4 right*
ST elevation >1 mm in lead V1 (sens 70% spec 100%)*

Can be seen after a proximal occlusion of the RCA.

V4 right is located at the same place as lead V4, but is placed on the right side of the patient. This means it is placed under the right nipple instead of the left. This increases the sensitivity of detecting right ventricle infarcts.

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Re: The 12 Lead ECG

مشاركةبواسطة دكتور كمال سيد » الأربعاء أكتوبر 31, 2018 10:46 pm


Anterior = V3 V4

Lateral = 1 V5 V6 aVL

Inferior = 11 111 aVF

Septal = V1 V2

Left Main = aVR

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Re: The 12 Lead ECG

مشاركةبواسطة دكتور كمال سيد » الأربعاء نوفمبر 07, 2018 9:47 pm

Recognition of AM I :

A) know what to look for :
1. ST elevation 1 mm or more
2. Two contiguous leads

B) know where to look :
1. In Lateral MI :

2. in Anterior MI :

3. in Inferior MI :

Normal ECG
1. Isoelectric ST seg & point
2. Upright T wave
3. No pathological Q wave

Evolution of AMI
# Acute : ST elevation
# Hours :
* ST elevation
* loss of R wave
* Q wave begins
# days 1 - 2 :
* T wave inversion
* Q wave deeper
# days later :
* ST normaizes
* T wave inverted
# weeks later :
* ST & T normal
* Q wave persists (pathological)

anterior wall ST elevation MI
1. ST elev in anterior leads at the J point
& sometimes in septal or lateral leads depending on the extent of MI
2. Reciprocal ST dep in Inferior leads (11;111;aVF)
Diagnosing a MI yu need to go beyond looking at rhythm strip & obtain a
12- lead ECG
Revised definition of MI
# acute , evolving OR recent MI
Either of the following :
1. Rise & OR fall of biomarkers WITH ONE of the following :
a) ischemic symptoms
b) Q waves in ECG
C) ECG indicative of ischemia (st elev or dep)
D) imaging evidence of loss of viable myocardium or RWMA "Regional Wall Motion Abnormalities"
2. Pathological findings of MI
ST seg elevation
1. 1 mm above baseline in LIMB leads
2. 2 mm above baseline in CHEST leads 0.08 sec to the Rt of J point
3. Look for in two or more leads facing same area







MORE ECG images ... =654&dpr=1

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اشترك في: الخميس إبريل 04, 2013 10:28 pm

Re: The 12 Lead ECG

مشاركةبواسطة دكتور كمال سيد » الأربعاء نوفمبر 07, 2018 10:47 pm





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