Lecture 8

Question 1

What is the SA node composed of and what does it connect to?

Answer 1

Composed of special cardiac muscle fibers; connects directly to atrial fibers

Question 2

What is the resting membrane potential of SA node fibers and what is threshold?

Answer 2

Resting: -55 to -60 mV
Threshold: -40 mV

Question 3

What is the ventricular fiber resting potential?

Answer 3

-85 to -90 mV

Question 4

What do you call action potentials that originate anywhere other than the SA node?

Answer 4

Ectopic focus or pacemaker

Question 5

What part of the heart is parasympathetic innervation distributed to and what neurotransmitter does it use?

Answer 5

SA and AV nodes; acetylcholine

Question 6

What part of the heart is sympathetic innervation distributed to and what neurotransmitter does it use?

Answer 6

All parts of the heart, but mainly the ventricles; norepinephrine

Question 7

What does the P wave in an EKG represent?

Answer 7

Atrial depolarization

Question 8

What does the QRS wave in an EKG represent?

Answer 8

Ventricular depolarization and it hides atrial depolarization

Question 9

What does the T wave in an EKG represent?

Answer 9

Ventricular repolarization

Question 10

What does the P-Q interval represent?

Answer 10

Time from SA node firing to ventricles firing (usually .16s)

Question 11

What does the Q-T interval represent?

Answer 11

Time from ventricular depolarization to repolarization (usually .35s)

Question 12

Connections of limb lead 1 and what direction does it measure?

Answer 12

Negative terminal on right arm
Positive terminal on left arm
Looks at the heart from right to left

Question 13

Connections of limb lead 2 and what direction does it measure?

Answer 13

Negative terminal on right arm
Positive terminal on left leg
Looks at the heart from upper right to lower left

Question 14

Connections of limb lead 3 and what direction does it measure?

Answer 14

Negative terminal on left arm
Positive terminal on left leg
Looks at the heart from upper left to lower left

Question 15

Definition of a vector

Answer 15

Arrow that points in the direction of the electrical potential generated by the current flow with the arrowhead in the positive direction; length of the arrow is proportional to the voltage of the potential

Question 16

What is the angle (direction) of lead 1?

Answer 16

0 degrees

Question 17

What is the angle (direction) of lead 2?

Answer 17

60 degrees

Question 18

What is the angle (direction) of lead 3?

Answer 18

120 degrees

Question 19

What is the mean electrical axis of the heart and in what direction does it measure?

Answer 19

59 degrees; direction of the electrical potential from negative to positive is from the base of the ventricles toward the apex

Question 20

What is another name for the atrial T-wave?

Answer 20

Atrial depolarization; hidden by the QRS wave of ventricles

Question 21

What can cause deviations from the mean electrical axis of the heart?

Answer 21

Change in position of heart in the chest
Hypertrophy of one ventricle
Bundle branch block
Fluid in pericardium

Question 22

What is a high voltage EKG and what is the most common cause?

Answer 22

Occurs when the sum of voltages of all the QRS complexes of the 3 standard leads is greater than 4 mV; most common cause is hypertrophy of the ventricle

Question 23

What causes a decrease in voltage of the heart?

Answer 23

Cardiac myopathies and conditions surrounding the heart

Question 24

What causes QRS waves to be longer than normal (bizarre complexes)?

Answer 24

Hypertrophy or dilation of the left or right ventricle as a result of destruction of cardiac muscle and replacement by scar tissue or multiple small blocks in the conduction impulses at many points in the purkinje system

Question 25

What abnormalities cause current of injury?

Answer 25

Mechanical trauma, infectious processes, and ischemia (most common)

Question 26

What effect does current of injury have on a QRS complex?

Answer 26

Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles

Question 27

What is the J point on an EKG?

Answer 27

Reference point for analyzing current of injury; occurs at the very end of the QRS wave and is the point at which all parts of the ventricle, including the injured areas, have become depolarized