ECG LP 04

Question 1

MYOCARDIAL ISCHEMIA (I)

Answer 1

Definition = an imbalance between the myocardial oxygen supply (from arterial blood) and the demand.
Causes:
1. A reduction in blood flow:
- obstruction of the coronary arteries (thrombus, embolus)
- stenosis (atheromatous plaque).
- increased coronary vascular tone.
2. An increase in the demand: exercises, tachycardia.
3. Hypoxia (reduced oxygen supply).
Typically there is an association, in different proportions, of decreased supply and increased demand, that determines myocardial ischemia

Question 2

MYOCARDIAL ISCHEMIA (I)

Answer 2

The myocardium depends almost entirely on aerobic metabolism.
The subendocardium is more vulnerable to the ischemic damage than the
subepicardium
- the anatomic distribution of arterial supply (the subendocardium is most distal);
- the subendocardium/subepicardium flow ratio is reduced when the arterial supply is reduced.

Question 3

ECG CONSEQUENCES OF THE ISCHEMIC HEART DISEASE

Answer 3

Ischemia = T wave changes;
injury = ST changes;
necrosis = pathological Q wave.
- They are ECG terms and must not be mistaken with the anatomo-pathological description!

These changes appear typically in a group of localized leads (left/lateral leads,
inferior leads, anterior leads, right leads) depending on the affected territory, and ultimately, depending on the artery that irrigates the respective territory (these will be described under the topography of myocardial infarction).

Question 4

ISCHEMIA = T WAVE CHANGES

Answer 4

1. Subendocardial ischemia = positive, symmetric and more pointed T wave.
2. Subepicardial ischemia = negative, symmetrical and more pointed T wave.
3. Non-specific T wave changes: flat T waves, either positive or negative; biphasic T waves

Question 5

SUBENDOCARDIAL ISCHEMIA

Answer 5

The affected area remains longer electronegative during repolarization generating vectors that will be registered by the exploring electrode close to the area.

Question 6

SUBEPICARDIAL ISCHEMIA

Answer 6

If the affected area is subepicardium, the local electrode will register a negative wave and a negative, symmetric, pointed T wave will be recorded in the respective leads.

Question 7

INJURY = ST CHANG

Answer 7

• Subendocardial injury = depressed ST segment; j point is also depressed; the depressed ST segment can be horizontal, descending or ascending.
• Subepicardial injury = elevated ST segment; j point is also elevated; the elevated ST segment can be horizontal, ascending or convex

Question 8

SUBENDOCARDIAL INJURY

Answer 8

• The affected area is later depolarized and remains longer electro positive. The local electrodes will register the vector. The vector is oriented from minus to plus.
• If the affected area is subendocardial, the local leads will register a depression of the ST segment.

Question 9

SUBEPICARDIAL INJURY

Answer 9

If the affected area is situated subepicardial, the local electrode will record a ST segment elevation.

Question 10

NECROSIS = PATHOLOGICAL Q WAV

Answer 10

A Q wave that doesn’t have the normal q wave criteria should be regarded as pathological (except aVR).

Pathological Q wave:
>1/4 of following R;
>3 mm deep in V5,6,
>0.04 seconds
Sometimes we can consider as pathological a q wave that still fulfils the normal criteria if it is a new acquisition, if it is associated with suggestive ST and T changes or if it appears in a suggestive clinical context.
The pathological Q wave is associated with a transmural myocardial infarction (MI) – a acute obstruction of a coronary artery that affects its territory from subendocard to subepicard.

Question 11

SOSSSS NECROSIS = PATHOLOGICAL Q WAV

Answer 11

The pathological Q wave is associated with a transmural myocardial infarction (MI) – a acute obstruction of a coronary artery that affects its territory from subendocard to subepicard.

Question 12

MIRROR-IMAGES (RECIPROCAL CHANGES)

Answer 12

If the local leads will register a ST elevation, the opposite leads register the opposite
image = a ST depression. But we should never consider a ST elevation as a mirror
image of a ST depression.

If the local leads will register a Q wave, the opposite leads register the opposite
image = an R wave.

Examples of pairs of opposite leads:  Lead III and aVF vs. Lead I and aVL  V1 and V2 vs. V6, V7, V8

Question 13

MYOCARDIAL INFARCTION

Answer 13

‚Natural’ evolution of a transmural MI = Q wave MI – the evolution without treatment.

There are four phases:

1. superacute phase;
2. acute phase;
3. subacute phase;
4. chronic phase.

We must take note that, depending on the affected territory, the changes will appear only in certain leads (e.g. in inferior MI the direct or typical modification will
appear in inferior leads: LIII, aVF, LII).

Question 14

1. SUPERACUTE PHASE

Answer 14

Duration: 0 – 6 hours (the first 6 hours).

ST elevates gradually until it includes T wave and forms a Pardee wave (the great monophasic wave).

Question 15

2. ACUTE PHASE

Answer 15

Duration: 6 hours – 2 weeks from.
Pathological Q wave is present. ( there are exceptions – cases with precocious apparition of Q wave, in the first 6 hours).
The ST segment is elevated, then gradually comes closer to the isoelectric line (at the end of this phase ST is isoelectric).
T wave starts to descend, and becomes negative.

Question 16

3. SUBACUTE PHASE

Answer 16

Duration: 2 weeks – 2 months. 
Pathological Q wave is present.
ST segment is isoelectric.
T wave is negative.
ST segment can remain elevated (in case of a ventricular aneurysm)

Question 17

4. CHRONIC PHASE

Answer 17

Duration: from 2 months onwards.
Pathological Q wave is present.
In some cases (20%) Q wave can disappear, leaving no trace of the MI

Question 18

STEMI = ST ELEVATION MI

Answer 18

STEMI is more recent term which underlines the importance of ST elevation.

A majority of patients with STEMI develop Q waves and follow the typical ECG evolution previously described.
Some patients with STEMI don’t develop Q waves; Some modifications of QRS complex can appear in these cases, such as diminution in R wave height.

Question 19

NSTEMI = NON-ST ELEVATION MI

Answer 19

There are cases of myocardial infarction without ST elevation:  ST depression;  negative T waves.

The difference between NSTEMI and unstable angina is made using biological markers for necrosis (e.g. cardiac troponins).
It is important to remember that the diagnostic of acute coronary syndromes is based on clinical signs, ECG and biological markers.

Question 20

ARTERIAL DISTRIBUTION IN MYOCARDIUM

Answer 20

Left main coronary artery:

• LAD (left anterior descendant artery): anterior wall of LV, anterior part of the septum, a part of anterior wall of RV, right bundle brunch and the 2 left fascicles.
• circumflex artery: lateral part of anterior wall, lateral wall and part of posterior wall of LV.

Right coronary artery (generates the posterior descendant artery):
posterodiafragmatic wall of LV; most of RV, posterior part of the septum, AV node, His bundle, left posterior fascicle, posterodiafragmatic wall of LV.

Question 21

TOPOGRAPHY OF MI (I)

Answer 21

Septum MI: Typical ECG modifications in V1, V2
Anterior MI:
- Typical ECG modifications in V3, V4.
- The affected artery: LAD
Antero-lateral MI (or anterior-extended):
- Typical ECG modifications in V1, V2, V3, V4, V5, V6, LI, aVL.
- The affected artery: LAD in its proximal segment.
Antero-inferior MI:
- Typical ECG modifications in precordial leads and in inferior leads.
- This happens in situations in which LAD is supplying the distal portion of the inferior wall.
Inferior MI:
- Typical ECG modifications in inferior leads.
- In most cases the affected artery is the right coronary or posterior descending artery. Usually posterior descending artery is a branch of right coronary artery; in a minority (~10%) of cases, the posterior interventricular artery is a branch of the circumflex coronary artery.
- In LI and aVL we can find reciprocal changes.

Question 22

TOPOGRAPHY OF MI (II)

Answer 22

Lateral MI:
- Direct image of MI in LI, aVL, V5, V6.
- The affected artery: circumflex artery.
Infero-lateral MI:
- Direct image of MI in inferior leads, V5, V6.
- an occlusion of the circumflex artery (= a left dominance) or an occlusion of right artery if the affected right artery has extensive posterolateral branches that supply a part of the lateral wall (= a right dominance).

Question 23

TOPOGRAPHY OF MI (III)

Answer 23

Posterior MI:
- Reciprocal changes in V1: tall R, depressed ST segment, positive T wave.
- Direct image of MI: in posterior leads V7, V8.
- Usually this region is supplied by posterolateral branches of right coronary artery, from its distal segment.
RV infarction:
- Typical image: in V1, V2, V3R, V4R, V5R.
- The affected artery: right coronary artery, proximal. A distal obstruction of right coronary artery is usually associated with inferior MI.

Question 24

DIFFERENTIAL DIAGNOSIS OF MI

Answer 24

QS waves in V1, V2 +/- ST elevation. 
 -  Anterior MI. 
 -  LBBB. 
 -  LVH. 
 - WPW syndrome B. 
Tall R and ST depression in V1. 
 -  Posterior MI. 
 -  RBBB.
 -   RVH. 
 -    WPW syndrome A.