EKG-Session 1

Question 1

Contractility

Answer 1

ability of heart muscle fibers to shorten, generate force, and pump blood

Question 2

Automaticity

Answer 2

ability of heart tissue to independently and rhythmically generate electrical impulses

Question 3

Conductivity

Answer 3

distribution of electrical impulses throughout the heart via a conduction system

Question 4

Excitability (irritability)

Answer 4

ability of cardiac cells to respond to external stimuli: chemical, mechanical, or electrical

Question 5

Polarized (resting) state

Answer 5

Interior of the myocyte is negatively charged

Question 6

Depolarization

Answer 6

Interior of the myocyte becomes positive
Influx of Na+ ions
Results in myocardial contraction

Question 7

Repolarization

Answer 7

Recovery phase
Interior of the myocyte returns to negative charge
Accomplished by transfer of potassium (K+) ions out of the myocytes

Question 8

What is an absolute refractory period?

Answer 8

• QRS to peak of T wave

- Myocardial cell will NOT respond to further stimulation

Question 9

What is relative refractory period?

Answer 9

• Downslope of T wave

- Some cardiac cells depolarized; can be stimulated to depolarize with a stronger-than-normal stimulus

Question 10

What is a supernormal period?

Answer 10

Weaker-than-normal stimulus can depolarize

Question 11

Explain the principle of automaticity.

Answer 11

Each structure within the conduction system:

• Conducts electrical activity at a specific velocity
• Can initiate electrical activity independently at a characteristic discharge rate
• Under appropriate conditions, each structure could act as a pacemaker

Question 12

Explain the concept of Overdrive suppression

Answer 12

Suppression of the automaticity and independent depolarization of cells with pacemaker potential by tissues firing at a higher intrinsic rate of automaticity.

Overdrive suppression explains why the SA node normally functions as the pacemaker of the heart, despite the presence of other tissues with automaticity

Question 13

What is the inherent rate of spontaneous depolarization of the Sino-Atrial (SA) node?

Answer 13

60-100min

Question 14

What is the inherent rate of spontaneous depolarization of the Atrial Cells?

Answer 14

60-75/min

Question 15

What is the inherent rate of spontaneous depolarization of the Atrioventricular node?

Answer 15

40-60/min

Question 16

What is the inherent rate of spontaneous depolarization of the Ventricular cells?

Answer 16

30-45/min

Question 17

What does the horizontal axis of an EKG record?

Answer 17

time

Question 18

What does the vertical axis of an EKG record?

Answer 18

voltage/velocity

Question 19

Fast response cardiac action potentials work through what type of channels?

Answer 19

Sodium

Question 20

Slow response cardiac action potentials work via what types of channels?

Answer 20

Calcium

Question 21

Where in the heart do slow response cardiac action potentials occur?

Answer 21

SA and AV nodes

Question 22

Where in the heart do fast response cardiac action potentials occur?

Answer 22

normal myocardial fibers in atria, ventricles, and Purkinje fibers

Question 23

Describe ‘positive deflections’ with regards to measuring velocity on an EKG.

Answer 23

Record impulse moving toward positive electrode

Deflections above the baseline

Question 24

Describe ‘negative deflections’ with regards to measuring velocity on an EKG.

Answer 24

Record impulse moving away from positive electrode

Deflections below the baseline

Question 25

How many limb leads are there?

Answer 25

6

Question 26

List the 3 bipolar leads

Answer 26

Lead I, II, III

Question 27

List the 3 Augmented limb leads

Answer 27

Lead aVR-Augmented voltage (right) Lead aVL-Augmented voltage (left) Lead aVF-Augmented voltage (foot)

Question 28

Describe chest lead placement for V1

Answer 28

4th intercostal space, right sternal border

Question 29

Describe chest lead placement for V2

Answer 29

4th intercostal space, left sternal border

Question 30

Describe chest lead placement for V3

Answer 30

Midway between V2 and V4

Question 31

Describe chest lead placement for V4

Answer 31

5th left intercostal space, mid-clavicular line

Question 32

Describe chest lead placement for V5

Answer 32

Midway between V4 and V6

Question 33

Describe chest lead placement for V6

Answer 33

5th left intercostal space, mid-axillary line

Question 34

Atrial depolarization

Answer 34

Represented by P wave on EKG strip Results in atrial contraction (SA node firing, wave spreading through atrium, results in atrial contraction)

Question 35

Atrial repolarization

Answer 35

Lost in QRS complex on EKG strip

Question 36

QRS Complex

Answer 36

Ventricular depolarization | (Impulse travels from AV node through bundle branches and Purkinje fibers, Results in ventricular contraction

Question 37

Q Wave

Answer 37

First negative deflection after the P wave

Question 38

R Wave

Answer 38

First positive deflection after the P wave

Question 39

S Wave

Answer 39

Negative deflection after an R wave

Question 40

T Wave

Answer 40

``` Electrical deflection following QRS complex Normally positive (upward) -Represents the rapid phase of ventricular depolarization ```

Question 41

U Wave

Answer 41

Follows T wave -Perkinje repolarization -Usually NOT present May indicate clinically relevant pathology (HYPOKALEMIA)

Question 42

What does the PR Segment represent?

Answer 42

Isoelectric (at the baseline) End of P wave to beginning of QRS complex Represents delay of electrical impulse through the AV node (allows time for ventricles to fill with blood)

Question 43

Where does the PR Interval occur on an EKG strip and what does it represent?

Answer 43

located from the beginning of P wave to beginning of QRS complex Represents atrial contraction and AV node delay Intervals are horizontal lines and therefore measurements of TIME or DURATION

Question 44

What is the normal duration of a PR Interval?

Answer 44

0.12-0.20 seconds Less than 5 small boxes/less than 1 big box Varies with heart rate

Question 45

Where does the QRS interval occur on an EKG strip and what does it represent?

Answer 45

Beginning of Q to end of S Represents ventricular depolarization Very Rapid

Question 46

What is the normal duration of a QRS interval?

Answer 46

Less than or equal to 0.12 seconds (3 small boxes)

Question 47

Where does the ST segment occur on an EKG strip and what does it represent?

Answer 47

From the end of the QRS to the start of the T wave Represents initial phase of ventricular repolarization Normally isoelectric Elevation or depression often clinically significant

Question 48

Where does the QT Interval occur on an EKG strip and what does it represent?

Answer 48

From the start of the QRS complex to the end of the T wave Represents ventricular depolarization/repolarization

Question 49

What is the normal duration of a QT interval?

Answer 49

Should be 0.30-0.44 seconds Should be less than half of the R-R interval Corrected for rate (QTc)

Question 50

Where does the R-R interval occur on an EKG strip and what is its significance?

Answer 50

Distance from one QRS complex to next | Used to calculate rate