Mean Electrical Axis

Question 1

What is a lead? (ECG)

Answer 1

The stretch between two limbs (arm or leg) electrodes

Question 2

What is Einthovens triangle?

Answer 2

-used to determine the electrical axis of the heart

• Einthoven named the leads between the 3 limb leads electrodes “standard lead I, II, III” referring to the two arm electrodes and the left leg electrode
  
  • he studied the relationship between theses electrodes forming a triangle where the heart electrically constitutes the null point

Question 3

What is the mean axis of depolarization?

Answer 3

• the average direction of depolarization during the cardiac cycle
  
  • can be done by observing the voltages of the ARS complex from two different perspectives using two different leads
  • Lead I: horizontal axis from left arm to right arm
  • Lead II: Axis from Right arm to left leg
  • Lead III:axis from left arm to left leg

Question 4

What is the normal mean electrical axis of the ventricles?

Answer 4

0 and 90 degrees

Question 5

What is ventricular hypertrophy?

Answer 5

• enlargement of one ventricle shifts the mean axis of depolarization toward the hyperthyroid ventricle because it takes longer to depolarize the larger ventricle
  
  • a left axis deviation occurs when the left ventricle is hypertrophied
  • a right axis deviation occurs when the right ventricle hypertrophies

Question 6

What is a bundle branch block?

Answer 6

• a conduction block in one of bundle of His, depolarization will be much slower in the blocked ventricle.
  
  • In the left bundle -branch block, depolarization will occur more slowly in the left ventricle than the right ventricle, and the mean electrical axis will deviate to the left
  • in the right bundle branch block, there will be a right axis deviation

Question 7

What is a myocardial infarction?

Answer 7

-deviations of the electrical axis occur to varying diseases