Case 2 Diagnostics Flashcards
What does MRI stand for?
Magnetic Resonance Imaging
How does an MRI work?
Powerful magnet releases a burst of electromagnetic energy causing the hydrogen atoms in the patient to be in their high energy state. As some hydrogen atoms return to their low energy state, they release energy which is detected.
What are some advantages of MRI?
Good for soft tissues, CNS and PNS; no ionising radiation; usable in pregnant women; excellent quality of detail
What are some disadvantages of MRI?
not good for areas without much water; presence of metallic objects in prohibited; expensive; resource heavy; claustrophobic; patient needs to be as still as possible
How does an ultrasound work?
Probe emits ultrasound, reflect various amounts from different surfaces (eg they pass through air and reflect lots from bone) and reflected waves are picked up by receiver.
What is the Doppler effect?
Objects moving away or closer changes the frequency of a wave
Why is the Doppler effect useful in ultrasonography
It can show arterial and venous blood flow.
What are the advantages of ultrasound?
cheap, portable, no ionising radiation
What are the disadvantages of ultrasound?
user dependent; limited by patient BMI; not good if the surrounding or superficial tissues are of a high echogenicity (bone)
How does plain radiography work?
X-rays are generated by electrons colliding with the end of a tube. X-rays penetrate through the body to varying degrees. X-rays are detected (used to be by a photographic film or plate, now by a digital detector)
What are the advantages of plain radiography?
cheap, quick, good for when there is an air background (eg near the lungs)
What are the disadvantages of plain radiography?
ionising radiation, 2D (pathologies could be hidden or missed), not good for soft tissues/hollow organs or neurological system
What does CT stand for?
Computed Tomography
How do CT scans work?
X-rays at different levels. Plain films are fed into a processor to generate a 3D image.
What are the advantages of CT scans?
3D, relatively simple, quick, less resource heavy
What are the disadvantages of CT scans?
difficulty in producing accurate images of soft tissue, lots of ionising radiation
How does echocardiology work?
Ultrasound of the heart, with the probe placed between the patient’s ribs or down the oesophagus.
What are the advantages of echocardiology?
Can see the heart in real time, and can use Doppler effect to visualise blood flow so good for assessing valvular disease.
How does coronary angiography work?
Peripheral artery is punctured with a hollow needle. Coronary catheter wire is then passed through into the artery, up to the aortic root and into the coronary vasculature. Radioplaque dye in injected into each coronary root. The dye is a dense liquid which blocks X-rays. Plain radiography is then used to image blockages in the coronary vasculature can be visualised.
How do you place the electrodes for a lead I ECG?
+ve electrode on left arm
-ve electrode on right arm
ground on right foot
How do you place the electrodes for a lead II ECG?
+ve electrode on left foot
-ve electrode on right arm
ground on right foot
How do you place the electrodes for a lead III ECG?
+ve electrode on left foot
-ve electrode on left arm
ground on right foot
How do you place the electrodes for an aVF ECG?
+ve electrode on left foot
-ve electrodes on left and right arms
How do you place the electrodes for an aVL ECG?
+ve electrode on left arm
-ve electrodes on right arm and left foot
How do you placer the electrode for an aVR ECG?
+ve electrode on right arm
-ve electrodes on left arm and left foot
How do you calculate rate on an ECG?
300/(no. of squares between Rs)
What are the 4 waves on an ECG?
P wave
QRS complex
T wave
U wave
What physiological event causes the P wave?
Atrial depolarisation
What physiological event causes the QRS complex?
Ventricular depolarisation
What physiological event causes the T wave?
Ventricular repolarisation
What is the normal length of a PR interval?
120-200ms
What does a U wave show?
An abnormal or ectopic beat
What is a normal QRS duration?
ideally 80-100ms
should be less than 120ms
In a healthy heart, is the ST segment flat, raised or lowered?
flat
Why do we need to use a corrected QT interval?
The QT interval is affected by heart rate, so QTc is used
What is the normal QTc in men?
greater than 440ms
What is the normal QTc in women?
greater than 450ms
What are the characteristic features of first degree heart block on a ECG?
PR interval greater than 200ms
What are the characteristic features of second degree heart block Mobitz I on an ECG?
PR interval extends till a QRS is dropped
What are the characteristic features of second degree heart block Mobitz II on an ECG?
PR interval doesn’t extend, QRS is occasionally dropped
What are the characteristic features of third degree heart block on an ECG?
no correlation between p and QRS
What are the characteristic features of atrial fibrillation on an ECG?
no p waves and irregular rhythm
What are the characteristic features of ventricular fibrillation on an ECG?
completely irregular
What are the characteristic features of supraventricular tachycardia on an ECG?
regular rhythm, fast, p waves get lost in t waves, tall thin QRS
What are the characteristic features of ventricular tachycardia on an ECG?
broad QRS longer than 120 ms
What are the characteristic features of hypertrophy on an ECG?
tall R, deep S, some leads have inverted T
What are the characteristic features of ischaemia on an ECG?
ST depression
What are the characteristic features of a STEMI on an ECG?
ST elevation
What are the characteristic features of an NSTEMI on an ECG?
normal or ST depression or T inversion or no ST elevation
What are the symptoms of arrythmias? (4)
Palpitations, dizziness, lightheadedness, SOBOE
What are the symptoms of cardiomyopathy? (2)
Fatigue, SOBOE
What are the symptoms of endocarditis? (4)
Fever, splinter haemorrhages, weightloss, new murmur
What are the symptoms of heart failure? (3)
SOB, peripheral oedema, orthopnoea
What are the symptoms of MI?
‘tight’ or central chest pain, radiating to neck and left arm, not relieved by rest
What are the symptoms of valvular disease? (3)
SOB, new murmurs, collapse
How long are the squares on an ECG?
small squares 40ms larger squares (5 small squares) 200ms
What are the symptoms of ischaemia/angina?
central chest pain on exertion, relieved by rest
