Aneurysms, hypertension and stroke Flashcards
What is hypertension?
Sustained elevation of systolic and diastolic blood pressure (> 140/90mmHg)
What are primary and secondary causes of hypertension?
- No identifiable primary cause - idiopathic
- Secondary - renal disease, adrenal tumours, aortic coarctation, steorid Rx
How can hypertension cause organ damage? (vessels, heart, lungs, kidney, eye, brain) [brief]
- Vessels - atheroma, aneurysm, elastic reduplication
- Heart - left ventricular hyeprtrophy, LHF
- Lungs - pulmonary oedema due to LHF
- Kidney - nephroscelerosis, renal failure
- Eye - retinal capillary damage, haemorrhages, exudates
- Brain - microaneurysms, stroke, ischaemic cortical atrophy
What is hypertensive heart disease?
When increased load causes concentric left ventricular hypertrophy. This can lead to heart failure.
What happens in hypertensive nephropathy?
Granular cortical atrophy due to nephrosclerosis - loss of a glomerulus causes atrophy of the nephron.
What happens in hypertensive retinopathy as it gets worse?
- Early - nicking of retinal veins by overlying arterioles, normally they run alongside.
- Moderate - straightened, wider capillaries, flame shaped haemorrhages, ‘cotton wool’ spots, hard exudates around macula
- Late chronic/malignant - Papilloedema, haemorrhage
What change in parameter of an arteriole can alter the systemic arterial blood pressure, thus causing hypertension?
Luminal diameter - resistance of flow is equiv to the fourth power of the diameter.
What is the difference between atherosclerosis and arteriosclerosis?
Atherosclerosis is the narrowing of the artery because of plaque build-up, a disease of the intima.
Arteriosclerosis refers to the general hardening/thickening of the artery walls, so atherosclerosis is a type of it.
Does atheroma cause hypertension?
Atheroma tends to affect larger blood vessels so does not increase TPR, so unlikely to cause hypertension. The two diseases are often encountered together though.
What happens to blood vessels (arterioles) in hypertension? What is hyaline arteriosclerosis?
Resistance arterioles show elastic duplication in hypertension.
Plasma exudes into the intima and deeper layers of the wall (media), causing hardening and a ‘pink glassy’ structure. This is ‘hyaline arteriosclerosis’.
The endothelium in hypertension is subject to damage by shearing forces applied by high cardiac output: atheroma is likely to develop at sites of endothelial damage due to hypertension.
What 3 things stimuate renin release by the kidney juxtaglomerular complex?
- Low renal blood flow/pressure
- Low blood Na+
- Sympathetic NS
How do you get from renin to angiotensin II?
- Angiotensinogen cleaved to angiotensin I
- By enzyme renin
- Angiotensin I activated to angiotensin II
- by ACE (from lung)
How does angiotensin II increase blood pressure?
- Vasoconstriction of resistance vessels
- ALDOSTERONE -> inc water reabsorption
- ADH -> inc water reabsorption
- thirst -> inc blood volume
- cardiac hypertrophy
- SNS -> noradrenaline inc
What signals negative feedback in the renin-angiotensin-aldosterone system?
Natriuretic peptides (ANP, BNP) released by the heart
How can ACE inhibitors (-pril) result in a dry cough as a side-effect?
As ACE is released from the lung surfaces, ACE inhibitors result in bradykinin build up within the lung and cause irritation resulting in a dry cough.
What is an aneurysm?
A bulge in the wall of a blood vessel
What is the difference between a ‘true’ and ‘false’ aneurysm?
True anuerysm is when all 3 layers of the blood vessel are affected, a false aneurysm is when not all 3 are affected, eg. it might be a punctured wall causing the bulge/expansion.
Describe ‘berry’ (saccular) aneurysms
- Typically occur at bifurcations of arteries - circle of willis
- Rupture -> subarachnoid haemorrhage
Describe microaneurysms
- Typically occur in cerebral arteries
- Patients with hypertension
- Rupture -> intracerebral haemorrhage
What is a cause of abdominal aortic aneurysm? What can rupture cause?
- Usually secondary to atheroma
- Rupture -> intraperitoneal haemorrhage -> death
- Can also throw off clots -> ischaemia / gangrene
What types of aneurysms result in a stretched aortic ring?
- Aortic dissection ‘dissecting aneurysm’
- Syphillitic aneurysm
Rupture -> haemopericardium and cardiac temponade
Why may an aneurysm not present as pulsatile?
Diminished due to thrombus or severe atheromatous thickening
At which locations do aneurysms occur?
In arteries and occasionally left ventricle (post MI) but very rarely in veins
What are points/factotrs of weakness that increase susceptiblity to aneurysms?
- usually due to atheroma
- sometimes inflammatory damage (eg syphilis)
- occsionally due to connective tissue abnormalities (Marfan’s)
- sometimes follow trauma eg. traffic accident
What are complications of aneurysms?
- Rupture
- Thrombosis
- Thromboembolism
Who is more likely to have aortic dissection (‘dissecting aneurysm’) in the population?
Elderly w/ medial degeneration or Marfan’s syndrome - a congenitally weak media
Describe aortic dissection and its consequences upon rupture
- Tear in the intima, typically aortic root, allows blood to enter the aortic wall and form a parallel track
- this may rupture back into aorta OR rupture through adventitia, causing cardiac tamponade (into pericardium) or exsanguination (into mediastinum)
Define ‘stroke’
Sudden onset of neurological deficit due to cardiovascular cause
What are modifiable risk factors associated with stroke?
- Hypertension
- Atrial fibrilation
- Smoking
- Diabetes mellitus
- High cholesterol
What are the two major types of stroke?
- Ischaemic (80%)
- Haemorrhagic (20%)
Describe the 3 types of ischaemic stroke
- Thrombo-embolic: eg thrombus over atheroma at carotid bifurcation; can be a mural thrombus from the heart (over MI)
- Primary occlusion of intracerebral artery/arteriole
- Lacunar (25%): occlusion of single penetrating artery, tiny lesions, silent, associated with white matter lesions and vascular dementia
What is the most common cause of haemorrhagic strokes?
Rupture of cerebral microaneurysm secondary to hypertension
What is the ischaemic penumbra?
The core of an infarct will undergo irreversible necrosis. The adjacent territory (penumbra) is only relatively ischaemic, as there may be a degree of compensation from nearby blood supplies.
We are trying to save the penumbra!
What is the timeframe for the ‘ischaemic penumbra’ to be salvaged if arterial perfusion is restored?
Within 3 hours, but some benefit to treatment up to 6 hours
What 3 factors do clinical effects of stroke depend on?
- Site
- Size
- Speed (of restoration of circulation of clot)
What are the 3 main sites at which herniation of the brain can occur in response to a space occupying lesion (massive bleed) in the brain?
- Beneath the FALX CEREBRI
- Through the TENTORIUM CEREBELLI
- Through the FORAMEN MAGNUM
What happens after liquefication necrosis of brain tissue due to strokes?
Macrophages clear the area, cystic spaces remain -> scarring
Describe lacunar infarcts
- Seen in diabetes, hypertension + extensive small vessel atheroma
- Affect deep penetrating arterioles - basal ganglia, brainstem, thalamus + deep white matter
- Not space occupying lesions
- Minimal additional symptoms due to small calibre vessels involved
What is a TIA?
- transient ischaemic attack - neurological deficit lasting 12-24 hours
- temporary but indication for immediate investigation and intervention
What constitutes the stroke management in hyperacute stroke units?
- Antiplatlet therapy (aspirin, clopidogrel, dipyridamole)
- Thrombolysis (best within 3 hours, may have functional benefit up to 6 hours later)
- Evacuation of clot
How can we prevent stroke in the population?
- Cigarette tax
- Aspirin for those at risk (Red of 25%)
- decrease salt intake
- treat atrial fib - warfarin
- fast recognition of TIA
Why is subarachnoid haemorrhage not considered a stroke on technical grounds?
As it involves vessels which are external to the brain itself. However, can produce spasm in cerebral arteries.
What are the types of intracranial haemorrhage?
- Extradural
- Subdural
- Subarachnoid
- Cerebral contusion
- Multiple petechial
What is the difference between subarachnoid and subdural haemorrhage?
Subarachnoid often follows ruptured berry aneurysm; blood is confined beneath pia/arachnoid and follows brain contours.
Subdural formation is result of trauma. Blood clot lies between arachnoid and dural meninges.
Watershed zone infarcts occur due to hypoperfusion at the boundaries of arterial territories. In what 3 organs are they most common?
- Colon
- Heart
- Brain
What are the 3 areas affected by watershed zone infarctions in the brain?
- Anterior, middle and posterior cerebral artery territory
