Heart function and imaging Flashcards
Examples of ways to image the heart
Echocardiography
Chest X-ray
Coronary CT Angiography
Invasive Coronary Angiogram
Coronary angioplasty
What are the advantages of echocardiogram?
Easy
Quick
Non-invasive
Non ionising radiation
To assess the heart
When is an echocardiogram ordered?
One of the first tests a cardiologist is likely to do to a patient admitted to the cardiac care unit
Who performs an echocardiogram?
Well trained cardiologist
What is an echocardiogram used for?
Identifying which areas of the heart have been damaged during MI
How that damage affects the heart’s function
What parameters are assessed during an echocardiogram?
LV function
RV funciton
Hypokinesis
Valve function
What about LV function can be observed during an echocardiogram?
Size
Well at pumping blood out the heart
What is hypokinesis?
Symmetry in the movement of the heart wall
May be damaged following MI
What is an ultrasound?
Uses sound waves in the megahertz range
1-15 MHz - inaudible to humans
How does an ultrasound work?
An ultrasound generates, detects and processes the ultrasound signal
Why is the image quality compromised in obese patients?
Image resolution is better with shorter wavelengths of sound, but this reduces the distance they can penetrate the tissue
Ultrasound image quality is compromised in patients with lots of adipose tissue
How does the ultrasound machine generate ultrasound?
Pizoelectric crystal cells generate and receive ultrasound signals
A very short electrical impulse is applied to the crystal-containing transducer
This generates a short pulse
The beam diverges and reflects off the surfaces it meets
What is a common pizoelectric crystal used in ultrasound?
Zirconate titanate
Changes dimension in response to an applied electric current
What is attenuation?
Sound waves lose energy to the medium they are travelling through
Velocity of the sound waves depend on the density of the medium
This is how we get different colours in the monitor image
What is a hyperechoic surface?
A highly reflective surface such as bone
Need to think carefully where to place the probe
Place the probe between the ribs to get a good image of the heart
Most of the ultrasound wave is reflected back, which casts an acoustic shadow behind the reflective structure
What is a hypoechoic or anechoic surface?
Very low or no reflection of the ultrasound wave
The probe’s inbuilt image compensation creates an area behind the surface of acoustic enhancement
Makes it appear brighter
What characteristics affect the reflected beams?
Reflected beams are altered by
- the distance they travel
- the structure they reflect from
- the characteristics of the media through which they have travelled
What can be seen in an echocardiogram?
Apex of the heart and four chambers
Valves
In infection can get enough detail to see the build up of bacteria on the valves on the echo
What are the benefits of echocardiograms?
Images can be freeze-framed
Can build all the data from an echo to obtain 3D pictures of the heart
Why are echocardiograms used so often to assess heart health?
Good modality to assess the structure of the heart and synchrony of the muscle of the heart wall in real time
How common are chest X-rays?
Common technique used for most patients
Are chest x-rays often used for patients suspected of having MI?
If unsure of the history can look at the anatomy
Why are chest x-rays not the first test done on suspected MI patients?
Time needed for the test - need to ensure the patient is stable
Shouldn’t hold up urgent treatment
What is a disadvantage of CXR?
Ionising radiation = inherent risk to the patient
Damaging to DNA and cells
Risk of mutations leading to cancer
What is another use for CXR in MI patients, other than diagnosis?
Used to check if complications have arisen from an MI
What is an example of a complication that arises due to MI?
Pulmonary oedema
Buildup of fluid inside the lungs
Bilateral increase in opaqueness as the heart is not pumping well enough
How much ionising radiation does a CT release compared to a CXR?
CT has 1000x more radiation than x-ray
How does a CXR create an image of the tissues?
Electromagnetic radiation with heterogeneous beams of x rays from a x ray generator
Aimed at particular tissue
Place a photographic or digital film
X-rays pass through tissue
Different types of tissue absorb x-rays at different extents
Shadow created in 2D picture allow us to investigate the tissues
What is a CT scan?
Imaging technique that takes multiple X-ray images around the craniocaudal axis
What is craniocaudal?
Head-to-tail
How does a CT make images of the body?
An X-ray machine is fixed opposite multiple rows of detectors
This rotates around the patient capturing X-ray images from different angles
Angles are computed using voxels
What is a voxel?
3D pixel
How are the x-ray images processed to form a CT image?
Axial slices are divided into grids of voxels
The attenuation in each is compared and calculated to reconstruct an optimised image
Post-processing algorithms can be used to highlight features and further optimise the image
What is attenuation?
How much the tissues absorb the radiation
What is a coronary CT angiography?
Newer technique of CT
Used to look for stenosis of the coronary arteries
Why are coronary CT angiography techniques used less than CXR or Echocardiograms?
Need quick sequencing CT machines to be able to obtain clear pictures of the heart
Which patients undergo cCTA?
Patients who present to A&E with low/intermediate probability for coronary artery disease
What is needed to carry out a cCTA?
Trace contrast
What is the advantage of cCTA?
Non-invasive
What is a disadvantage of cCTA?
Use of ionising radiation due to using X-rays
Currently quite a new technique = expensive
What happens if cCTA shows moderate or significant CAD?
Patients need further testes
- functional tests
- invasive coronary angiogram
How do you conduct an ICA?
Iodine-based contrast dye used to highlight the coronary arteries on X-rays
What is the aim of ICA?
Determine whether a blockage or narrowing has occurred in the coronary arteries
How is an ICA carried out?
A catheter is inserted into a blood vessel usually in the groin
Catheter is guided into the coronary arteries using X-rays
Positioned in the heart so that its tip rests in a coronary artery
Contrast is then injected
Artery and small vessels leading from it are visualized by a series of X-rays
What is the form of intervention that can be done during ICA?
Angioplasty
Which patients undergo angioplasty?
Patients who present to A&E with typical angina routinely have an invasive coronary angiogram
Following MI - gold standard for treatment
What is PCI?
Percutaneous Transluminal Coronary Angioplasty
Coronary Angioplasty
When is PCI used?
For severe (stable) angina where medication is ineffective - outpatient cases
Acute STEMI
NSTEMI ACS
Haemodynamically significant lesions serving viable myocardium observed during angiography
What are the complication risks of PCI?
Thrombosis occurs in 1-2% of patients
Usually presents as an MI, with high mortality
Restenosis occurs in up to 20% of patients, usually presents as a return of anginal pain
When is PCI carried out?
Usually carries on in patient undergoing angiography - in the same procedure
Steps of PCI
Performed under local anaesthetic
A catheter is inserted into an artery in the wrist or groin and guided into the affected coronary artery using continuous X-ray video
When catheter is in place a wire is guided into the affected coronary artery
Balloon is inflated to widen the artery
What is a stent?
Metal mesh tube placed around the balloon inflated in the coronary artery
Holds artery open
What are the complications of PCI?
Thrombosis occurs in 1-2% of the patients
Usually presents as MI, with high mortality
Restenosis occurs in up to 20% of patients
Bleeding in site of entry can lead to haematoma or aneurysm
Use serial x-rays images and dyes to visualise the arteries which causes increased risk of kidney damage
What are the symptoms of restenosis?
Return of anginal pain
What is restenosis?
Neointimal hyperplasia
Formation of thrombi
Another blockage = MI
What is neointimal hyperplasia?
Re-closure of the artery due to proliferation of smooth muscle cells
What are ways to prevent restenosis?
Coating stents in drugs to prevent complications
Localised amount of anti-clotting drugs
What is an example of a drug used in drug-eluting stents?
Paclitaxel
Inhibits cell proliferation
