Electrophysiology of the Heart

Question 1

What is preload?

Answer 1

ventricular filling (diastole).

Question 2

What is the directional orientation of the electrical conduction of the heart?

Answer 2

begins in posterior wall of right atrium, it starts to come forward, then turns backward toward your left heel. This is the normal vector.

Question 3

When a wave of energy is going toward a positive electrode, what does it show?

Answer 3

a positive deflection (upward)

Question 4

When a wave of energy is going away from a positive electrode, what does it show?

Answer 4

a negative deflection (downward)

Question 5

What node forms the P wave on the EKG?

Answer 5

the SA node

Question 6

What if there is greater than 3 boxes between QRS?

Answer 6

there is an interventricular conduction delay

Question 7

Should the ST segment be flat?

Answer 7

YES.

Question 8

Between what degrees should we see positive deflections?

Answer 8

down toward the belly button (0-110 degrees)

Question 9

If the heart is hypertrophied, will the EKG show a larger or smaller signal?

Answer 9

larger

Question 10

What would a pericardial effusion do to the EKG signal?

Answer 10

decrease it, because the fluid around the heart is blocking it.

Question 11

Should T waves normally be upright on an EKG on all leads?

Answer 11

YES (except avR).

Question 12

Does the Q wave have to be of significant dimensions to be indicative of an MI?

Answer 12

YES

Question 13

What can accessory pathways do to the conduction system?

Answer 13

shorten the PR interval or alter the QRS interval.

Question 14

If there is a right axis shift (due to right ventricular hypertrophy), what will happen to avL and lead I?

Answer 14

They will both be inverted.

Question 15

What is a dipole?

Answer 15

a separation of a positive and negative charge, and is led by the positive end. This positive end is going to go towards a positive electrode to form a positive (upward) deflection on the EKG.

Question 16

So, what does it mean if we see a positive deflection on an EKG?

Answer 16

There was positive current coming TOWARD a positive electrode.

Question 17

So, what does it mean if we see a negative deflection on an EKG?

Answer 17

There was a positive current going AWAY from a positive electrode.

Question 18

Why are the deflections in leads I, II, and III all positive in a normal EKG?

Answer 18

because the electrodes a placed such that when the depolarization travels from the SA node throughout the heart, it follows the direction of the + electrodes of Einthoven’s triangle. So any impulse traveling down and to the left on the body will show up as a positive deflection.

Question 19

What are the normal axial degrees for depolarization in a healthy heart?

Answer 19

-30 to 90.

Question 20

At what axis would the heart most likely be if there were huge QRS complexes in lead II?

Answer 20

60 degrees, because this almost matches the vector of lead II.

Question 21

At what axis would the heart most likely be if there were huge QRS complexes in lead III?

Answer 21

120 degrees, because this angle matches more closely with lead III.

Question 22

What does it mean if we see huge deflections in avR?

Answer 22

there is right axis deviation.

Question 23

What do the augmented leads each reflect?

Answer 23

Each corresponding corner of einthoven’s triangle as if everything else were negative and each of these were +. So, the deflection for aVR will be downward, the deflection for aVL will be a little of both (more downward though), and the deflection for aVF will be upward). Think if I follow the depolarization of the heart starting at the SA node, what would each of these corners pick up (designating each as positive).

Question 24

What will hyperkalemia (ex. giving a patient K+) do to the QRS complex?

Answer 24

Spread it out, and peak the T wave.

Question 25

What will hypokalemia (ex. from vomiting excessively) do?

Answer 25

Tighten the QRS complex (and lengthen QT interval) and you’ll see a “u” wave.

Question 26

What will hypercalcemia do to the EKG?

Answer 26

Pull everything together (shorten PR interval)

Question 27

What will hypocalcemia (ex. blocking Ca++ channels) do to the EKG?

Answer 27

prolonged PR interval.

Question 28

What is a sinus rhythm?

Answer 28

any cardiac rhythm where depolarization of the cardiac muscle begins at the SA node.

Question 29

What would you see in absence of the SA node?

Answer 29

just QRST; no P wave.

Question 30

What does a flat line on an EKG mean?

Answer 30

could be that the lead is perpendicular and the impulse is in the middle

Question 31

How do we remember colors for electrode placements?

Answer 31

Think cowboy hats: white= good guys on RIGHT arm, and black= bad guys on the LEFT arm.
Think traffic light for feet: green light= gas pedal, which you push with your RIGHT foot, and red light= clutch, which you push with your LEFT foot to stop.

Question 32

What do inverted T waves indicate?

Answer 32

ischemia

Question 33

What is a STEMI?

Answer 33

ST elevation