ECG

Question 1

describe what we are recording in the ECG

Answer 1

electrical activity of the heart

• the wave of depolarisation travels from the SAN through the atria, then goes ot the AVN, then it travels through the bundle of Left bundle His , then the RIGHT bundle of His, then the purkinje fibres

Question 2

what acts as a skeleton to the heart? describe it

Answer 2

• ANNULUS FIBROSIS
• 4 fibrous rings around ;

1. pulmonary valve
2. aortic valve
3. Right atrioventricular
4. Left atrioventricular

Question 3

describe the cellular charges changes and how this is marked in an ECG

Answer 3

• ECG is a positive electrode
• initially at rest the cell is more positive outside than inside, this is due ot the cell being more permeable to the potassium than sodium, alothough theyare both positively charged NA+ carries a stronger positive charge than potassium, so more positive outside than inside
• then we enter depolarisation , the sodium moves from outside to inside the cell, this makes the inside positive and the outside negative
• the wave of depolarisation travels through the myocytes from the SAN to the apex of the heart, this is movement of negative wave towards the electrode at LIMB LEAD 2, hence why it is registered as a positive deflection

Question 4

what are the limb leads , draw them

Question 5

what are the onducting systems of the heart and which takes over when

Answer 5

1. SAN - natural autonomaty , intrinsi rate of 60-100
2. AVN - only if SAN is firing, on the ECG you’d see that the rate is slower and theres no sinus rhythm 40-60bpm
3. ventricular myocytes - fire very slowly at 20-40 bpm

Question 6

draw and label the ECG pattern normal one and the length of each phase

Answer 6

p = atrial depolarisation 0.12-0.2

pr segment = 0.12-0.2

qrs = ventricular depolarisation

Question 7

describe what the parts of each segment on ECG represents and how long they last

Answer 7

• p = atrial depolarisation
• PT segment =
  
  • represents the time it takes for ventricles to fill
  • it acts as an isoelectric line
  • lasts 0.12-0.2 seconds (3-5 small bxes)
• Q = as the muscle in the interventricular septum depolarises from the left to the right
  
  • there can be a small downward deflection as the wave of electrical acitivity is moving to the sides and so away from the electrode and not towards it
• R = depolarisation of the apex of the heart and free ventricular walls, large due to the larger muscle mass, so if there was left sided hypertrophy then it would be larger
• S = depolarisation upwards to the bases of the heart,
  
  • negative due to the electrical activity moving away from the heart
• T = repolarisation of the ventricles ,
  
  • positive deflection because of the replusion of the electrical current since becomes more positive as NA+ moves out
  • also theres a driving force away from the electrode and towards the SAN and begins at the epicardial surface of apex of heart

Question 8

first downward deflection after the P wave

Answer 8

Q wc is a result of the electrical activity moving sideways as it depolarises the left and right muscles

Question 9

how do you calculate the HR of a regular ECG and irregular ECG

Answer 9

regular = peak from one R to next R e.g 4 big squares then do 300/4 = 75bpm

irregular count large 30 SQUARES a dn how many peaks there are in those squares, then x10

Question 10

where do you put the chest leads and what are they called?

Answer 10

precordial chest leads

• V1 =. right strenum ridge 4th intercostal space = gives anteroseptal right view
• V2 = left strenum ridge 4th intercostal space = gives anteroseptal left view
• V3 = inbetween V2 and V3 = gives anterior apex view of lV and RV
• V4 = 5th intercostal space midclavicular line =gives anterior apex wall of Rv and LV
• V5= 5th intercostal space anterior axilllary line = gives lateral LV view
• V6= 5th intercostal space midaxillary line = gives lateral LV view of heart

Question 11

what view and artery can supplies the rejoin of view of the precordial leads and limb leads

Answer 11

• V1= anteroseptal RV = LAD
• V2 = anteroseptal LV = LAD
• V3 = distal lad anteroapical view
• V4 = LAD anteroapical (apex of RV and LV)
• V5 = circumflex
• V6= circumflex +proximal LCA
• limb lead I= proximal LCA and circumflex
• limb lead II = RCA inferior aspect of heart
• limb lead III = RCA inferior aspect
• AvF= RCA inferior view
• AvL= circumflex and proximal LCA anteriolateral
• AvR = / /

Question 12

necrosis of the right wall? wc leads

Answer 12

II, III, AvF

Question 13

occlusion of LADwc leads?

Answer 13

V1 V2 V3 V4

Question 14

damage to left wall

Answer 14

AvL, V5 V6 L1 (bold = best at looking at left side of heart

Question 15

damage to posterior aspect of heart, wc lead?

Answer 15

R wave would be taller and peaked more than in V1 V2 because posterior aspect of heart supplied by RCA

but not always the case

Question 16

draw a whole ecg script and label wc parts have wc artery and view

Answer 16

V1 V2 septal (RCA)

V3 V4 anterioapical (apex of LV and RV, LAD)

V5 V6 (anterolateral -proxmial LCA and circumflex artery)

L1 = RCA wave of left lateral

L2 = RCA e activity from atria to apex

L3 = inferior aspect RCA

AvR = / artery

AVL= similar to L2 but opposite side,

AvF= inferior asepect

Question 17

whats the difference between what the augmented limb leads measure and the limb leads

Answer 17

augmented measure voltage difference from central reference terminal and skin electrode

limb leads measure voltage difference between the leads(since theres a positive and negative electrode)

Question 18

whats the isoelectric line

Answer 18

when whole cell is depolarised and there is no current flow