ECG basics- Electrodes and waves

Question 1

Intrinsic rates of heart tissues

Answer 1

-heart beats the same rate as the fastest intrinsic cell rate
-therefore in a healthy individual HR is dictated by SA node
-SA node= 60-100 bpm
-Atrial cells= 55-60 bpm
-AV node= 45-50 bpm
-His bundle= 40-45 bpm
-Bundle branch= 40-45 bpm
-Purkinje cells= 35-40 bpm
-Myocardial cells= 30-35 bpm

Question 2

Lead placement

Answer 2

Red- right arm
Yellow- left arm
Green- left leg
Black- right leg
V1- 4th intercostal space to right of sternum
V2- 4th intercostal space to left of sternum
V3- between V2 and V4
V4- 5th intercostal space midclavicular line
V5- anterior axillary line same horizontal level as V4
V6- mid axillary line on same horizontal level as V4

Question 3

Leads I, II, III

Answer 3

Lead I= difference between red and yellow lead
Lead II= difference between red and green lead
Lead III= difference between yellow and green lead

Question 4

Augmented leads

Answer 4

aVR, aVL, aVF
-wilson central terminal= reference point that is the average of the limb lead electrode potential
-WCT calculated by averaging electrical potential of electrical currents from 2 electrodes that aren’t the positive electrode

Question 5

How a wave is formed

Answer 5

-reference electrode is negative
-exploring electrode is positive
-electrical vector directed towards exploring electrode
-therefore positive deflection
-same the other way round but would cause negative deflection (downward wave)

Question 6

ECG paper

Answer 6

Y axis= voltage
1mm= 0.1mV
X axis= time
1mm= 0.04s

Question 7

Chest leads

Answer 7

-measured from WCT to chest electrode