Myocardial Infarction Flashcards
What is the first step in diagnosing acute MI?
ECG
What is the crucial part of the ECG to diagnosing MI?
ST segment
What should the normal ST segment look like?
Should be the same height as the PR interval and the isoelectric line
What happens to the ST segment in an MI?
ST elevation
What else is used to diagnose MI and why?
The presence of troponin I or T (cardiac specific) as when heart cells burst/die these proteins are released
What is the coronary flow reserve?
Maximum amount of blood in the coronary blood flow
By how much can the coronary flow reserve increase?
5 fold
Why does angina happen on exertion?
Bc stenosis affects coronary flow reserve
When does coronary flow reserve increase normally?
During exercise
How does stenosis affect coronary blood flow?
After about 50% stenosis, the coronary flow reserve decreases so coronary blood flow can no longer increase as much - CFR decreases with increasing % stenosis
What causes the stenosis to increase from 50% to 100% in AMI?
Unstable clot/plaque - RBCs caught in fibrin net
What is chest pain due to in AMI?
Sensation of myocardial ischaemia
Where else is pain felt during an AMI?
Anterior chest, left arm, neck
Is the pain diffuse or localised and why?
Diffuse → nerve supply is somatic, no dermatomes, visceral nerve supply
What is the character of pain in AMI?
Tight, pressure, weight, constriction, dull
What triggers angina?
Exercise, cold, meals, psychological stress
What is relief for angina?
Rest, GTN
What causes shortness of breath in an MI?
Pulmonary oedema
What happens as the heart becomes increasing failing?
As LV EDP increases, CO increases less
Why does oedema occur?
Pressure on the venule end of capillaries → mean pressure increases → hydrostatic pressure increases
What happens when atherosclerotic plaque ruptures?
1) Endothelial layer feels back under sheer stress of exercise
2) Platelets starts accumulating on exposed atherosclerotic plaque which initiates the clotting casade
What is the difference between stable and unstable atherosclerotic plaque?
Stable plaque is separated from the lumen by a fibrous cap however in unstable plaque the fibrous cap is eroded
What state is the plaque in at body temp?
Liquid
What happens to unstable plaque?
1) Fibrous cap is eroded and communicated with the lumen
2) Cholesterol liquid is replaced by a blood clot
3) Intraplaque haemorrhage occurs which extends into the lumen of the coronary artery
What are 3 treatments for atherosclerotic plaque?
1) Statins (cholesterol lowering)
2) Anti-platelet drugs
3) Clot busters
How does cholesterol cause plaque?
1) Oxidised LDL is attacked by macrophages which think it is a foreign body
2) Activated macrophages induce intimal smooth muscle cell death and degrade matrix in the fibrous cap
3) Intimal smooth muscle cells become senescent
What drugs are used to lower LDL cholesterol by preventing the above process?
Statins
Why do you need anti-platelet drugs to treat plaque?
Because platelets aggregate at the site of rupture/erosin
What are anti-platelet drugs?
Aspirin and other drugs which work together with aspirin
When is aspirin given to treat AMI?
Immediately after ST elevation is seen on ECG (done in ambulance)
How much aspirin is given and how?
300mg orally (bc it is absorbed in buccal mucosa)
What happens after platelets aggregate at the site of rupture?
Thrombus forms and extends into the lumen and plaque
What is an example of a clot buster drug (thrombolytic) used for PE and stroke?
tPA (tissue plasminogen activator)
What is the problem with used a thrombolytic e.g. tPA?
You are marinating the body in a v potent drug which goes around the whole body and stops clotting aka the healing process around the body → risk of GI and intracranial haemorrhage
What happens when MI patient arrives at hospital?
Go to heart attack centre and direct to catheter labs for mechanical reperfusion (bypass A&E) bc time is muscle
Why is mechanical reperfusion better than pharmacological?
1) Faster reperfusion
2) Higher % reperfusion
3) Less stroke and bleeds
4) Lower mortality
What is mechanical reperfusion?
Inserting a stent?
What is the name of the mechanical reperfusion process used to treat MI?
Primary percutaneous coronary intervention
What is the most common presentation of AMI?
Chest pain
What are the two main types of MI?
1) STEMI (ST elevated MI)
2) NSTEMI (non-ST elevated MI)
Which type of MI is more serious?
STEMI
What are the two most important investigations when suspecting an MI?
ECG and troponin
What is used to diagnose a NSTEMI without ST elevation?
Troponin release
What is the diagnosis if there is no ST elevation and the troponin is negative?
Unstable angina
What is the diagnosis if there is ST elevation but the troponin is negative?
Aborted MI (v rare)
What do you do if someone has ST elevation?
Risk of MI but heart is in process of dying → medical emergency, take straight to cath lab for mechanical reperfusion
What do you do if someone has no ST elevation?
No occluded epicardial coronary artery so not a medical emergency until troponin comes back positive
How long does it take for troponin results to come back?
60 minutes
What do you need before making diagnosis of MI?
Troponin release shown
What is a myocardial infarction?
When there is evidence of myocardial necrosis in a clinical setting consistent with myocardial ischaemia
How do you diagnose MI?
- Detection of rise and/or fall of cardiac biomarkers (troponin) with at least one value >99th percentile of the URL together with evidence of myocardial ischaemia with at least one of…
1) Symptoms of ischaemia
2) ECG changes indicative of new ischaemia (ST or LBBB)
3) Development of pathological Q waves
4) Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
5) Identification of intracoronary thrombus by angiography or autopsy
What are the types of MI?
1) Spontaneous MI (plaque rupture, ulceration, erosion or dissection)
2) MI secondary to ischaemic imbalance (endothelial dysfunction, spasm, coronary embolism, fast or slow arrhythmias, anaemia, hypoxia, hypotension, high BP ± LVH (perioperative))
3) MI causing death before biomarkers available
4a) MI related to PCI
4b) MI related to stent thrombosis
5) MI related to CBG
What causes don’t lead to an MI?
Myocarditis, chemotherapy, cardioversion, trauma
What drugs improve supply demand balance of the heart?
Anti-anginals
1) Beta-adrenoreceptor blockers
2) L-type calcium channel blockers
3) Nitrates
4) ATP-sensitive potassium channel openers
5) Funny current channel blockers
What needs to happen/be given to stop a second heart attack or developing heart failure?
1) Lower cholesterol
2) Lower BP (ACE-I and beta blocker)
3) Aspirin ± ADP receptor antagonist → stops platelet activation
4) Beta blockers
5) Statins
6) Stopping smoking
7) Managing diabetes
What are examples of the big 5 classes of cardiology drugs which prolong life (secondary intervention?
1) Atorvastatin
2) Ramipril
3) Bisoprolol
4) Aspirin
5) Ticagrelor
Give an example of an ACE inhibitor
Ramipril
Give an example of a beta blocker
Bisoprolol
Give an example of a platelet ADP receptor antagonist
Ticagrelor
Given an example of a statin
Atorvastatin
What investigation usually leads to patients being advised to take statins?
CT coronary angiogram
What happens to the heart after an MI?
The heart dilates
What happens hours to days after an MI?
Expansion of infarct (ventricular remodelling)
What happens days to months after an MI?
Global (ventricular) remodelling
What accelerates ventricular modelling (heart dilation)?
Further plaque rupture
What happens to the cardiac wall after an MI?
The wall of the apex of the heart is much thinner after one apical anterior MI due to cardiac dilation? (good areas are those away from the area of infarction)
How many people in the UK aged >45 have definite HF?
650,000
What is the readmission rate in older patients?
Up to 50% in 6 months following discharge §
What are the non-modifiable CV risk factors?
Family history, age, sex
What are the modifiable CV risk factors?
Smoking, high cholesterol, high BP, diabetes, obesity, diet, exercise, excess alcohol
