L11 - Acute Coronary Syndrome Flashcards
Hypoxemia
- aerobic metabolism and oxidative phosphorylation inhibited
- ATP cannot be regenerated
- ADP & AMP accumulate and are subsequently degraded into adenosine
Effect of accumulation of adenosine (5)
- potent vasodilator
- binds to receptors on VSM
- decrease calcium entry into cell
- hence relaxation
- increased coronary BF
Examples of other chemicals resulting in vasodilation (4)
- CO2
- Lactate
- acetate
- H+
Describe endothelial cell dysfunction
- inappropriate vasoconstriction of coronary arteries
- loss of normal antithrombotic properties
Describe interaction between platelets and endothelial cells
Normal endothelium , aggregating platelets
Serotonin 5HT, Thromboxane TXA2
- contraction of VSM
- vasoconstriction
Describe the appearance of STEMI vs NSTEMI
NSTEMI - platelet rich, partially occlusive
STEMI - red thrombus, fibrin rich when clot is aspirated, totally occlusive
Symptoms of myocardial infarction
- acute central chest pain, crushing, gripping, tight
- chest pain radiates to arms, neck, jaw or epigastrium
- associated nausea, sweatiness, breathlessness, palpitations
3 main manifestations of atherosclerosis
- coronary
- cerebrovascular
- peripheral
Patient consequences of Coronary atherosclerosis
short and sweet, literally 3 words
MI
Angina
sudden death
Cerebrovascular atherosclerosis
TIA?
CVA?
TIA - Transient Ishcaemic attack
CVA - cerebrovascular attack (stroke)
Peripheral atherosclerosis may lead to.. (2)
Intermittent claudication (muscle pain on mild exertion)
Gangrene
Angina
- Ischaemic pain due to reduced blood supply to the heart muscle
- due to blocked coronary arteries,
Why does cocaine use increase the risk of heart attack?
Cocaine causes intense vasospasm in artery causing ishcaemia.
Silent infarct common in
Diabetics
Elderly
What do silent MI presentations include
notes
- Syncope (temp loss of consciousness) (rare)
- pulmonary oedema
- epigastric pain
- chundering
- post operative hypotension
- oliguria
- acute confusional state
- diabetic hyperglycaemic states
- stroke
Signs of STEMI in patients
e.g. how may they present?
Pallor
Sweatiness
Pulse - BP increased (pain, symp drive)
Pulse - BP decreased (hypotension, SA or AV node ischaemia)
What are the criteria needed to define Acute coronary syndrome ?
3 main points
- unstable, ischaemic, chest pain (history)
- ischaemic ECG changes
- raised cardiac biomarkers
Persistence of Q waves indicates
Manifestation of previous MI
Describe coronary artery anatomy
- Right coronary artery
- Left main coronary artery
- circumflex
- left anterior descending
Infarction in left main coronary artery may present with (3)
- Widespread ST depression
- ST elevation in AVR
- Cardiogenic shock
Infarction of circumflex coronary artery would come up where on ECG?
Silent?
Posterior
Lateral V5-V6, I, aVL
Inferior II, III, aVF
Infarction in left anterior descending coronary artery would come up where on ECG?
Anterior V1-V4
Septal
Lateral V5-6
aVL
What is the worst type of infarct & why?
LAD
- supplies LV
Describe classic anterior STEMI ECG?
Tombstoning
- ST elevation V1-V6
- reciprocal changes in II, III, AVF
How can troponin help differentiate between unstable angina & NSTEMI
Unstable angina - troponin negative, chest pain
NSTEMI - raised trop, not full ST elevation
What cardiac enzymes are used as markers of myocardial necrosis ?
When do the levels peak
Troponin
- produced by ventricular myocytes in response to stretch
- peak at 24-48hrs
Describe a suitable test for identifying re-infarction?
CKMB - creatine kinase MB
- enzyme found in heart muscle
- correlates well with amount of myocardial death
WHO classification of different types of MI
read
NEED TO KNOW
TYPE 1:
- spontaneous MI related to ischaemia due to a primary coronary event
TYPE 2:
- MI secondary to ischaemia due to either increased oxygen demand or decreased supply e.g. coronary artery
TYPE 3: - Sudden unexpected cardiac death - cardiac arrest - symptoms suggestive of myocardial ischaemia TYPE 4a - MI associated with PCI TYPE 4b - MI associated with stent thrombosis
Type 5
- Myocardial infarction associated with CABG
Acute management of ACS
- pre hospital
- in hospital
Pre hospital
- aspirin. GTN spray
In hospital
- morphine & metoclopramide
- oxygen if low sats
- GTN spray or IV
- antiplatelet agents
Metoclopramide
Symptomatic treatment of nausea and vomiting.
Chronic management of ACS (4)
- Dual antiplatelet therapy (DAPT)
- Statins (lower cholesterol)
- ACE I (left ventricle remodelling)
- Betablockers
Mechanism of action of aspirin
- Aspirin blocks production of Thromboxane A2 receptor. Enables aspirin to be sticky and aggregate.
- Action of aspirin on platelet COX-1 is permanent, lasting for the life of the platelet.
- thus preventing platelets sticking together.
Role of the P2Y12 receptor (3)
- recruitment of platelets
- potentiation of procoagulant activity
- potentiation of aggregation
Mechanism of clopidogrel
- irreversible inhibitor of the P2Y12 receptor
- pro-drug with slow onset of action
- superior to aspirin at secondary prevention of CV events.
Describe why there are differences on how patients will react to clopidogrel
- capacity of clopidogrel to inhibit ADP-induced platelet aggregation varies among subjects.
- variability due to genetic polymorphisms in the CYP isoenzymes involved in the metabolic activation of clopidogrel.
Prasugrel
- pro-drug, quicker onset
- greater, more predictable inhibition of ADP-induced platelet aggregation
Why is Ticagrelor now seen as a better anti-platelet therapy?
- different class of anti-platelet
- direct acting
- reversibly binds to P2Y12 receptor
- more rapid onset of action
- greater anti-platelet effect than clopidogrel
What is the effect that nitrates have?
- relaxes VSM by donation of NO, activating gyanylate cyclase, producing cGMP.
- dilation of coronary vessels improves oxygen supply to the myocardium
- dilation of peripheral veins, and in higher doses peripheral arteries.
- reduces preload and afterload
- thereby lowers myocardial oxygen consumption
Describe how nitrates are introduced into the body?
- sublingual or IV for rapid effect
- develop tolerance
