Supporting Life Flashcards
How do atherosclerotic plaques form? What happens to them over time?
Excess cholesterol ingested in the diet goes into the bloodstream and sinks into the cracks in blood vessel cell walls.
Over the years it bulges up and out into the artery gradually reducing blood flow.
What happens if there is mild blockage in a coronary artery?
Starved surrounding cardiomyocytes send signals to the coronary arteries causing them to grow new artery extensions (angiogenesis) in order to supply that area of heart muscle with blood.
How quickly does angiogenesis in the heart occur?
Around two days.
What causes an atherosclerotic plaque to rupture?
Turbulent blood flow due to increased heart rate and respiratory rate as a result of exertion.
What causes a complete blockage when an atherosclerotic plaque ruptures?
When the plaque ruptures, the cholesterol ‘sludge’ it was covering is released. Within moments blood platelets converge on the site forming a clot. This gets larger and larger and eventually causes a complete blockage.
What are the clinical signs of an acute myocardial infarction?
- Sense of impending doom
- Severe central crushing pain
- Pain radiating down the arms (mainly left), shoulders, neck or jaw
- Feeling of heartburn or indigestion (early sign)
- Dyspnoea (shortness of breath)
- Heart palpitations
- Sweating
- Syncope
- Increased heart rate
- Dizziness and disorientation (later sign)
What causes the drastic rise in heart rate during an acute MI?
The brain triggers a massive release of adrenaline into the bloodstream causing the increase in heart rate.
What happens to oxygen starved cardiomyocytes?
They die and rupture releasing troponin into the bloodstream.
What happens when the heart can no longer keep up with the oxygen demands of the body in an acute MI?
Pulse becomes weaker leading to pulmonary oedema and dyspnoea (breathlessness). This causes dizziness and disorientation.
How many heart cells are lost each second during an acute myocardial infarction?
500
What do ambulance staff give patients suffering an acute MI as a first line treatment?
300mg of aspirin that is chewed and absorbed via the buccal mucosa.
What is given to disperse a clot in an acute MI?
TPA (tissue plasminogen activator)
What can happen when the cardiomyocytes that were starved of oxygen during an acute MI are reperfused?
One of the cardiomyocytes can become a pacemaker beating out of time with the rest of the heart. This can cause VF.
How do you correct VF?
By shocking the heart with 130,000 watts with the intention to stop all activity in the heart and hope that the heart will start again in the correct rhythm.
What are the five electrical stages of the cardiac cycle?
1) PR interval
2) P wave
3) QRS complex
4) ST segment
5) T wave
What is the PR interval?
Where the electrical signal in the heart moves from the SA node and travels through the atria to the AV node. There is electrical silence as it travels through the intra-ventricular system and emerges through the perkingie fibres and triggers ventricular contraction.
What does the P wave represent?
Atrial depolarisation
What does the QRS complex represent?
Ventricular contraction
What is the ST segment?
A period of electrical silence where the heart muscle repolarises after ventricular contraction.
What does the T wave represent?
The repolarisation of the ventricles.
What is the iso-electric line?
The line of electrical silence between every PQRS complex after the T wave.
Why is the height of the ST segment important?
It is used to diagnose NSTEMI and STEMI.
What is the normal height of the ST segment?
It should be the same height as the PR interval and the iso-electric line.
What are the cardiac specific troponins that are used to diagnose MI?
Troponin T and I
What is the coronary flow reserve?
The ratio between rest flow and max flow. This is the maximum amount of increase in blood flow that the heart can cope with.
What amount of blood flow increase are normal healthy hearts capable of sustaining?
5-fold increase
How great does artery stenosis have to be in order to affect flow reserve?
80%
In terms of coronary flow reserve; why do symptoms of angina occur upon exertion?
Because the basal flow rate is not affected in arterial stenosis, just maximum vasodilation which is reached during exertion.
What are the clinical signs of angina (myocardial ischaemia)?
- Sudden onset central chest pain radiating to the left arm and/or jaw lasting LESS THAN 20-30 minutes
- Pain disappears during rest
- Shortness of breath
- Pain relief from GTN spray
What happens to patients that are given IV adenosine to combat tachycardia?
They experience constricting chest pain.
What is the association between ATP and angina?
In myocardial ischaemia, the ATP is not ‘recharged’ because there is not enough oxygen for the oxygen transport chain. This causes ADP to break down into adenosine.
High levels of adenosine in the heart is one of the contributing factors to angina.
For a given cardiac output, as the heart gets more diseased the heart compensates by having a higher _________________________?
Left ventricular end-diastolic pressure.
What does a higher left-ventricular end-diastolic pressure in ischaemic heart disease cause?
Increased pressure in venule end of capillaries –> increased mean pressure of capillaries –> hydrostatic pressure exceeds oncotic pressure –> net movement of fluid from capillaries to alveoli –> diffusion is prevented
How do atherosclerotic plaques form?
1) Activated macrophages (and sometimes smooth muscle cells) ingest oxidised LDLs as they thing it is a foreign body.
2) Phagocytosis causes inflammation.
3) Enzymes break down the extracellular matrix (fibrous cap).
4) Eventually the macrophages die and contribute to the ‘gruel’ in the middle of the plaque.