Lecture 12: Acute Myocardial Infarction Flashcards
What is myocardial infarction?
The interuption of blood supply to part of the heart, causing some heart cells to die
Where do thrombus form?
At the site of an atherosclerotic lesion, obstructing blood flow to the myocardial tissues
What can provide resistance to rupture?
Presence of smooth muscle cells in fibrous cap
What plaques are rupture prone?
Plaques rich in soft extracellular lipids
What is the triggering mechanism for the development of thrombus in patients with myocardial infarction?
Plaque rupture
What is infarct expansion?
A disproportionate thinning and dilation of the infarct zone
What is ventrical remodelling?
A disproportionate thinning and dilation of the ventricle resulting in an enlarged heart
What are the cellular changes associated with the initial myocardial infarction?
- The development of infarct extension
- Infarct expansion
- Ventricular remodelling
What is a NSTEMI?
A complete occlusion of a minor coronary artery or a partial occlusion of a major coronary artery previously by atheroclosis.
What does a NSTEMI cause?
Causes a partial thickness damage of heart muscle
What is STEMI?
Occurs by developing a complete occlusion of a major coronary artery previeoisly affected by atherosclerosis
What does a STEMI cause?
Full thickness damage of heart muscle
What are the symptoms of myocardial infarction? (5)
- Chest pain
- Nausea
- Vomiting
- Sweating
- Pain can radiate to neck, jaw, left arm, back
How do patients describe myocardial infarction?
- Squeezing
- Smothering
- Choking sensations
- Someone sitting on their chest
Is pain of myocardial infarction relieved by rest and sublingual GTN?
No
What causes GI complaints from myocardial infarction?
Due to sensitivity of pain and resulting vagal stimulation
How is acute MI diagnosed?
- Biochemical markers
- Laboratory tests
- ECG
What are the biochemical markers used to diagnose MI
- Rise and fall in troponin
- Rapid rise and fall in creatine kinase
What laboratory tests are used to diagnose MI?
- Troponin I levels
What is troponin?
Troponin T and I are components of the myofilament troponin complex. Released from damage
Describe troponin I levels during a myocardial infarction
- Rise in 3 hours
- Peak at 14 to 18 hours
- Remain elevated for 5-7 days
Describe troponin T levels during MI
Rise in 3-5 hours and stay elevated for 10-14 days
What are the iso forms of creatine kinase?
- CK MB1
- CK MB2
Where is CK MB1 found?
Plasma
Where is CK MB2 found?
Tissues
When does CK-MB appear in the serum?
6-12 hours
When does CK-MB peak?
Between 12 and 28 hours
When do CK-MB levels return to normal?
72 to 96 hours
What is myoglobin?
Oxygen binding protein
Where is myoglobin found?
Skeletal and cardiac muscle
When do myoglobin levels elevate?
Within 1-2 hours of MI
When do myoglobin levels peak?
3-15 hours
What is lactate dehydrogenase LDH?
A tetrametric protein, made up of two types of proteins
What happens to LDH during MI?
Levels elevate
Describe ECG during the early stage of MI?
- T waves become tall and narrow
- This stage is referred to as hyper-acute or peaked T waves
What happens to the ST segment of an ECG during MI?
ST levels elevate
What do Q waves represent?
Flow of electrical forces towards the septum
What can a persistent elevation of ST segment indicate?
Presence of a ventricular aneurysm
What will always indicate previous myocardial infarction
Q waves - they never disappear
How does myocardial ischaemia affect ECG?
- ST segment depression
- With or without T wave inversion as result of altered reploarizarion
How does myocardial injury affect ECG?
Causes ST segment elevation with or without loss of R wave
How does myocardial infarction affect ECG?
Causes deep Q waves of absence of depolarization current from dead tissue and receding currents from opposite side of heart
How long do Q waves take to develop?
Hours to days
What do Q waves show?
Presence of dead tissue and provide ECG evidence of a previous MI
