Week 1 - ECG Flashcards
What is the P wave?
atrial depolarisation
what is the QRS complex?
ventricular depolarisation
What is the T wave?
ventricular repolarisation
What does the ECG give us info about?
hearts rhythm and conducting system of the heart
What are standard limb leads and what do they tell us?
tell us info about events of heart - direction and prescence of depolarisation/repolarisation
What are the 3 limb leads?
(I) is left arm relative to right arm
(II) is left leg relative to right arm
(III) is left leg relative to left arm
How many leads are there on an ECG and what are they?
3 limb leads (I, II and III), 3 augmented limb leads (aVR, aVL and aVF) and 6 chest leads (V1-V6)
What are waves of depolarisation shown as on an ECG?
depolarisation towards the electrode sticker causes an up-going blip on ECG.
depolarisation away from a sticker causes a down-going blip
repolarisation is the opposite - away is up-going blip and towards is down-going blip
What is the PR interval?
start of P to start of QRS. 0.12-0.2s
What is the QRS complex and its duration?
time taken for entire ventricle to depolarise. 0.08s
What is the QT interval?
start os QRS to end of T. changes depending on BPM. its 0.42s at 60BPM.
What is the significance of standard limb lead II?
its axis is most similar to that of the direction of depolarisation in the heart, so it has the largest R wave. this is also the rhythm strip
Why is the p wave upward going?
depolarisation is towards leg
Why is the q wave downward going in II?
depolarisation is from middle to outside of heart - opposite direction to leg
Why is the R wave upward going in II?
bundle of his moved depolarisation down the heart, in direction of leg
Why is the S wave downward going?
final direction of contraction is from base up towards intraventricular septum
Why is the T wave upward going?
repolarisation of the ventricle is moving away from the leg, from bottom upwards. upward going blip
Whats the significance of augmented limb leads?
shows 1 limb lead with respect to the other 2 combined. aVF is left foot relative to the midline between right and left arm leads
What are the precocial chest leads and what do they tell us?
gives info about spread of depolarisation on a horizontal plane rather than a frontal plane. V1-V6. V6 is upward going because depolarisation from heart moves that way. V1 is downward going because depolarisation goes in opposite direction
What is a STEMI?
ST segment elevation myocardial infarction. if ST segment is elevated, there is a myocardial infarction.
What is 1st degree heart block?
PR interval increased, so longer than 0.2s. SA to AV node delay. conduction still occurs
What is 2nd degree heart block?
PR interval gradually increases and then fails and QRS doesn’t occur. ventricle occasionally doesn’t contract
What is 3rd degree heart block?
no AV conduction. QRS still occurs as pacemakers in ventricle take over and cause contraction. atria and ventricles contract independently
What is an atrial flutter?
atria depolarises a lot faster than it should - 6/7 P waves and then a QRS complex. causes supraventricular tachycardia
What is atrial fibrillation?
pacemaker fails to spread depolarisation around atria so it contracts uncoordinatedly, all at different times. no clear P wave and QRS happens randomly
What is ventricular fibrillation?
most serious. uncoordinated contraction of ventricles, heart not pumping blood to brain so unconscious quickly.
Why do you use a defibrillator?
it depolarises all cells at the same time to give SA node opportunity to restart sinus rhythm. necassary when in fibrillation.
