Clinical Cardiac MI Flashcards
MRI and CT scanning are relatively
recent
How does a MR scanner work?
- Very strong, superconducting magnet of 0.5-3T.
- Radio-frequency coils transmit signals into patient, and energy the body absorbs is received by surface coils.
- In a metal ‘faraday’ box to exclude internal RF (same as fm stations)
- A computer is then used to reconstruct the images
- ECG signal for cardiac imaging
Super conducting Magnets
Enormous tube of iron
- bathed in liquid helium
- zero-electrical Resistance
- Magnetic-field always on! only turned off when heated (dangerous)
- Large refrigeration plants required
- Emergency vent for He to boiled off
Safety concerns.
- Magnetic field strong enough to launch projectiles
- Risk to electronic implants: pacemakers/defibrillators, cochlear implants
- Metallic foreign bodies: eyes, pre-80s cerebral aneurysm clips.
Particular problems with cardiac imaging
- Small fast-moving structures
- Constant cardiac motion (gated images)
- Resp motion
- irregular cardiac rhythms (blurry heart)
- Patients inability to co-operate
- Claustrophobia
Simplest type of image to take?
Axial image
Calcium is
black
If patients don’t hold their breath, you get a
Blurry image
Ventricular modeling
Take many images from different planes, and calculate volumes
green: endocardial surface
blue: epicardial surface
What happens when intima pulls away from aorta
Most people 50% die. New channel, can pull away right the way down.
Right ventricular cardiomyopathy
accumulate lipids in myocardial cells. liable sudden ventricular arrhythmias.
-Irregular crenulated ventricular lining.
Fibroma
Benign fibrous tumour
Delayed myocardial enhancement.
Give people contrast agents: Gd-contrast agents
- Image 10-30mins later
- how much GD depends on how much extracellular space is there, shows as white (normal should have very little!)
Used: in adult cardiology for MI and assessment of myocardial viability
Lesser Use: to assess cardiomyopathy and possible causes, degree of myocardial fibrosis, myocarditis
angiography
3D image
Coronary angiogram
- Dye injected
- can see small arteries, outline =the lumen!
How do we treat coronary artery disease?
Coronary Bypass
Take arteries/veins, attach one end to aorta and the other to coronary arteries
Metal stents
Hold arteries open
Vein vs arterial grafts
Vein grafts clot within 5-10 years, arterial grafts much better
Balloon coronary angioplasty
- Balloon dilation of an atheromatous stenosis
- Requires extensive anticoagulant therapy (aspirin and heparin)
- High risk of acute thrombosis at the angioplasty site
- High risk of re-stenosis long-term, more scar tissue (~4-6months post procedure)
Factors that promote restenosis
- Multiple lesions treated
- Lengthy lesions
- diabetes increase risk by 3x
- previous history of re-stenosis
Now what is done more the ballon coronary angioplasty?
ballon with drug covered stent
Coronary stents
- Placed to ensure continued patency at site
- Reduces re-stenosis effect and need for re-intervention
- Still risk of acute thrombosis or restenosis.
Done with large antiplatelet drug to reduce thrombus + one month oral therapy
Many varieties
Advantages of CT angiography
-Non-invasive, therefore cheap, and lower risk
- Images both vessel wall and lumen
- More pleasant for patient
- Visualised other thoracic pathology.
- Lower radiation and contrast load
- Non-specific so can be used for whatever
Disadvantages of CT angiography
- Need regular slow cardiac rhythm, (doesn’t work with atrial fibrillation)
- Required patient co-op
- problems with heavily calcified vessels
- More difficult to interpret
Plaque in coronary artery
White calcified plaque with lipid out line
