Lecture 13- ECG changes during myocardial ischaemia Flashcards by Saskia Chapman

Q

Coronary artery narrowing or occlusion lead to

A

ischemia or infarction (necrosis

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Q

changes in the ECG can be seen in

A

leads facing the affected area

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

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Q

ischaemia

A

lack of oxygen to muscle but no muscle necrosis

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Q

myocardial infarction

A

muscle necrosis due to ischaemia

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Q

blood test markers in ischameia

A

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

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Q

blood test markers in MI

A

blood tests will be positive for cardiac troponins

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Q

STEMI

A

ST segment elevation MI

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Q

Non-STEMI

A

Non-ST segment elevation

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Q

Which ECG leads face which parts of the ventricles?

Inferior surface of ventricles

A

II, III and aVF

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Q

Which ECG leads face which parts of the ventricles?

Septum and anterior surface of ventricles

A

V1, V2, V3, V4

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Q

Which ECG leads face which parts of the ventricles?

Right ventricle and septum

A

V1 and V2 and aVR

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Q

Which ECG leads face which parts of the ventricles?

Apex and anterior surface of ventricles

A

V3 and V4

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Q

Which ECG leads face which parts of the ventricles?

Lateral surface of the ventricles

A

I, aVL, V5

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Q

ST segment elevation Myocardial infarction (STEMI) occurs due to

A

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

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Q

ECG changes in STEMI

A

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

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Q

Evolving ECG changes in a STEMI

A

Q

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

A

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

Q

Are all Q waves pathologic

A

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

Q

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

A

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

Q

Pathologic Q waves

A

>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)

Q

A

Q

types of acute coronary syndrome

A

stable angina
unstable angina
NSTEMI
STEMI

Q

stable angina

A

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

Q

unstable angina

A

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

NSTEMI

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

STEMI

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

same changes on ECG for both

ischamei and NON-STEMI

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

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

ECG changes in NSTEMI

ST segment depression and T wave inversion On ECG tracing behaves as if abnormal current traversing damaged tissue is moving away from recording electrode

ECG changes in stable angina

* 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