Lecture 14

Question 1

What did Einthoven do

Answer 1

Discovered the ECG by attaching sensors to skin attached to a silver wire going through a magnetic field. The wire showed vibrations which was given a shape once a light beam was shown across the wire. This was the QRST wave

Question 2

How do action potentials spread throughout the myocardium?

Answer 2

Myocardial cells are connected by intercalated disks which contain gap junctions. Action potentials spread through these gap junctions

Question 3

Route of action potential in the heart

Answer 3

1. SA node (atrial contraction)
2. AV node (ventricular contraction->slowed)
3. Bundle of His
4. Purkinje fibers (fast conduction)

Question 4

ECG deflection patterns

Answer 4

1. Current is parallel to lead (same direction)
   -ECG stylus moves strongly upwards
2. Current is parallel to lead (opposite direction)
   -ECG stylus moves strongly downwards
3. Current is oblique to lead
   -Smaller deflection in the given direction
   -Size depends on how close the vector is to
   the axis

Question 5

What decides the magnitude of the deflection (physiologically)

Answer 5

The direction of the current as well as the amount of tissue surrounding the current