Lecture 13- ECG changes during myocardial ischaemia

Question 1

Coronary artery narrowing or occlusion lead to

Answer 1

ischemia or infarction (necrosis

Question 2

changes in the ECG can be seen in

Answer 2

leads facing the affected area

Need to look at the P, QRS and T or all 12 leads

Question 3

ischaemia

Answer 3

lack of oxygen to muscle but no muscle necrosis

Question 4

myocardial infarction

Answer 4

muscle necrosis due to ischaemia

Question 5

blood test markers in ischameia

Answer 5

will be negative for markers of myocyte necrosis (cardiac troponins)

Question 6

blood test markers in MI

Answer 6

blood tests will be positive for cardiac troponins

Question 7

STEMI

Answer 7

ST segment elevation MI

Question 8

Non-STEMI

Answer 8

Non-ST segment elevation

Question 9

Which ECG leads face which parts of the ventricles?

Inferior surface of ventricles

Answer 9

II, III and aVF

Question 10

Which ECG leads face which parts of the ventricles?

Septum and anterior surface of ventricles

Answer 10

V1, V2, V3, V4

Question 11

Which ECG leads face which parts of the ventricles?

Right ventricle and septum

Answer 11

V1 and V2 and aVR

Question 12

Which ECG leads face which parts of the ventricles?

Apex and anterior surface of ventricles

Answer 12

V3 and V4

Question 13

Which ECG leads face which parts of the ventricles?

Lateral surface of the ventricles

Answer 13

I, aVL, V5

Question 14

ST segment elevation Myocardial infarction (STEMI) occurs due to

Answer 14

• Due to complete occlusion of coronary artery
• Full thickness of myocardium involved

Question 15

ECG changes in STEMI

Answer 15

• Results in a positive deflection (going up)
• ST elevation is earliest sign of STEMI
• Indication for intervention

Question 16

Evolving ECG changes in a STEMI

Answer 16

Question 17

Why does myocardial necrosis and scar tissue from evolving and old infarcts leads to pathologic Q waves?

Answer 17

No electrical activity in dead tissue

No AP and no electrical current

ECG looks through dead tissue and picks up electrical forces from opposite side of infarcted heart

Question 18

Are all Q waves pathologic

Answer 18

NOOOOOO

Small Q weaves represents normal left to right depolarised of the interventricular septum (typically seen in lateral leads- I, aVL, V5-6)

Deeper Q waves (>2mm) may be seen in leads III and aVR as normal variant (should not have any Q waves in lead V1-3)

Q wave is any negative deflection that precedes an R wave

Question 19

Are all q waves a sign of an old infarct or depolarisation of septum?

Answer 19

• NO
• Pulmonary embolism may also lead to q waves in lead 3- part of the classic ECG findings for PE
  
  • S wave in lead I
  • Q wave in lead III
  • Inverted T wave in lead III

Question 20

Pathologic Q waves

Answer 20

• >1 small square wide (>40 ms)
• >2 small squares deep (mV)
• Except leads III and aVR- slightly bigger Q waves may be normal in these leads)

Question 22

types of acute coronary syndrome

Answer 22

1. stable angina
2. unstable angina
3. NSTEMI
4. STEMI

Question 23

stable angina

Answer 23

angina pain develops if there is an increased demand in the setting of a stable atherosclerotic plaque e.g. exercise

Vessel is unable to dialte enough to allow adequate blood flow to meet myocardial demand

Question 24

unstable angina

Answer 24

plaque ruptures and a thrombus froms around the ruptures plaque causing aprtial occlusion of the vessel. Anginal pain occurs at rest or progresses rapdily over a short period of time

Question 25

NSTEMI

Answer 25

during an NSTEM, the palque rupture and thrombus formation causes partial occlusion ot the vessel that results in injury and infarct to the subendocardial myocardium

Question 26

STEMI

Answer 26

complete occlusion of the blood vessel lumen, resulting in transmural injury and infacrt to the myocardium, which is reflected by ECG changes and a rise in troponin

Question 27

same changes on ECG for both

Answer 27

ischamei and NON-STEMI

Question 28

how can sevre ischamia (unstable angina) be differentiated from NON-Stemi

Answer 28

Differentiate by blood test for myocyte necrosis - troponin I/T

Question 29

ECG changes in NSTEMI

Answer 29

ST segment depression and T wave inversion

On ECG tracing behaves as if abnormal current traversing damaged tissue is moving away from recording electrode

Question 30

ECG changes in stable angina

Answer 30

• ST depression during exercise because of coronary disease- but stable atherosclerotic plaque causing fixed narrowing
  
  • Exercise can be on a Treadmill (exercise stress test) or chemically induced (dobutamine stress test)
  • ECG changes will reverse at rest
  • ECG: down sloping of ST-segment depression or elevation