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level: Level 1

Questions and Answers List

level questions: Level 1

QuestionAnswer
What threshold is needed to overcome in the cardiac myocyte to generate a action potential-70mv
General overview of the movement of AP in the myocardiumActivity starts at the SA node Depolarisation occurs and spreads around the atria To the AV node Where there is a delay of 120ms After the delay, activity spreads down the septum and then over the ventricular myocardium From the inside surface to the outside surface After about 280ms the cells start to repolarise
Why when using a ECG, you can only see depolarisation and repolarisationSince it is put on the skin, hence only drastic changes in potential can be seen e.g. depolarisation and repolarisation
What is the direction of spread of a action potentialAtria --> Ventricle Endocardial cells --> Epicardial cells
If you put a electrode on the apex, what would atrial depolarization look likeatrial depolarisation will produce a small upward deflection Small since it is a small muscle Upward since it is moving towards the electrode P wave
If you put a electrode on the apex, what would spread from septum look likeExcitation spreads about halfway down the septum, then out across the axis of the heart Produces a small downward deflection because : Downward because it is moving away Small because not moving directly away Q wave
If you put a electrode on the apex, what would spread through the ventricular myocardiumdepolarisation spreads through the ventricular muscle along an axis slightly to the left of the septum produces a large upward deflection Upwards since it is moving towards Large because : Large muscle moving directly towards electrode R wave
What would you see at the end of depolarisation in a ECGdepolarisation finally spreads upwards to the base of the ventricles produces a small downward deflection Downward because moving away Small since it is not moving directly away S wave
What would ventricular repolarisation show on a ECGproduces a medium upward deflection upward because moving away since it is opposite of depolarisation medium because timing in different cells dispersed T wave
What are all the parts of the ECGP wave - atrial depolarisation Q wave - septal depolarisation spreading to ventricle R wave - main ventricular depolarisation S wave - end ventricular depolarisation T wave - ventricular repolarisation
Why cannot you see atrial repolarisationIt gets overshadows by QRS complex hence does not show
Why does the location of the electrode matter?This is because, the location of the electrode can affect the direction and size of the actual pulse
What are the different locations and views6 chest electrodes- V1-V6 which show 6 views of the heart 4 limb electrodes --> I, II, III, aVF, aVL, aVR