Unit 2: Overview of Cardiac Conduction System

Question 1

Automaticity

Answer 1

allows the cardiac cells to generate an impulse

Question 2

Sinoatrial Node (SA)

Answer 2

pacemaker of the heart

-60 to 100 bpm

Question 3

Atrioventricular Node (AV)

Answer 3

40 to 60 bpm

• the gatekeeper of the hearts electrical conduction system
• responsible for allowing impulses to travel between the atria and the ventricles
• if SA node fails, the AV node can generate impulses at a rate of 40 to 60 bpm

Question 4

Ventricular Cells (Left and Right bundles of HIS, the Purkinje fibers, and Ventricles)

Answer 4

20-40 bpm

Question 5

Excitability

Answer 5

the ability to respond to a stimulus and generate an impulse

Question 6

Conductivity

Answer 6

allows cardiac tissue to transmit the impulses to neighboring connected cells

Question 7

Cardiac Action Potential

Answer 7

a process in which the membrane potential, the difference in charge between the inferior and exterior of the cell, changes or goes up and down in a consistent pattern
-a stimulus begins the movement that produces the cardiac action potential

Question 8

Depolarization

Answer 8

the movement of ions proceeding and facilitating cardiac mechanical contraction

Question 9

Repolarization

Answer 9

the movement of ions back to the resting state

• the cardiac resting membrane potential of -90 mV, to allow for the initiation of another action potential
• 5 phases of the action potential

Question 10

Absolute refractory (means resistant) period

Answer 10

cells are unresponsive (during and after depolarization)

Question 11

Refractory Period

Answer 11

a greater than normal stimulus my initiate an impulse

Question 12

Electrocardiogram (ECG)

Answer 12

graphic representation of the hearts electrical activity

• has 12 leads/views of the electrical activity in the heart
• each lead has a (+) and (-) electrode or pole; electrical impulse is measured as it moves between 2 poles/points
• electrical impulse moves towards a (+) pole, the waveform will be upright on the ECG
• if the electrical impulse is moving away from the (+) pole it will produce a downward or negative (-) deflection of the ECG
• best lead to identify the hearts rhythm is lead II (2)
• Lead II: mimics the hearts natural electrical direction in a healthy, normal positioned heart

Question 13

What is the best lead to identify or interpret the hearts rhythm?

Answer 13

lead II

Question 14

Waveforms on a ECK/EKG

Answer 14

1. P wave
2. QRS complex
3. T wave
4. U wave

Question 15

P wave

Answer 15

first wave that is normally seen

• represents the SA node sending out an electrical impulse
• atrial depolarization
• should be upright (positive deflection) with a rounded top in lead II
• not be longer than 0.10 sec
• no higher than 2.5 mm

Question 16

QRS Complex

Answer 16

2nd waveform

• ventricular depolarization
• normal: pointy and skinny in width
• wide QRS: (greater than 0.10 sec or two and a half small boxes wide) means there is something occurring in the ventricles causing the QRS to widen
  ex: may indicate that the impulse originated in the ventricles or that there is a block in the ventricles delaying the impulse from traveling through the ventricles to allow for normal depolarization

Question 17

T wave

Answer 17

after QRS complex

• ventricular repolarization
• wave should be upright and rounded in lead II
• helpful in monitoring electrolyte imbalances (hypo/hyperkalemia), disturbances with myocardial oxygen supply, or other cardiac disorders (pericarditis or ventricular aneurysm)

Question 18

U wave

Answer 18

rarely seen

• represents purkinje fiber repolarization
• can be seen w/ certain medication toxicities (digoxin) an electrolyte imbalances (hypokalemia)
• small rounded wave in lead II
• can be confused with P wave

Question 19

Intervals in a ECG/EKG

Answer 19

• PR Interval
• QRS Interval
• QT Interval

Question 20

PR Interval

Answer 20

from the beginning of the P wave to the beginning of the QRS complex

• reflects time it takes an electrical impulse to depolarize the atria and travel to the ventricles
• 0.12 to 0.20 sec (5 small boxes on ECG)

Question 21

QRS Interval

Answer 21

measure of time to depolarize the ventricles

• measured from where the QRS leaves the baseline to where it returns to baseline
• 0.06 to 0.12 sec
• greater than 0.12 (equal to or more than 3 small boxes) may be a sign of disturbance within the ventricle itself or blockage
• atrial repolarization is “buried” in the QRS complex

Question 22

QT Interval

Answer 22

measure of time it takes the ventricle to depolarize and repolarize

• measured from where the QRS leaves the baseline and where the T wave returns to baseline
• less than or equal to 0.52 seconds (13 small boxes)
• never more than half the distance from one QRS to the next

Question 23

Steps In ECG Interpretation

Answer 23

Ask the following

• is the rate fast, slow, or normal?
• is the rhythm regular; are complexes an equal distance from one wave to the next?
• distances from P wave to P wave equal throughout strip? (P-P interval)
• distances from QRS wave to QRS wave equal throughout strip? (R-R interval)
• P waves present?
• QRS complexes present?
• T waves present?
• are the intervals within normal limits? (e.g. PR interval (0.12 to .20 sec), QRS interval (0.6 to 0.12 sec))
• is there a P wave before every QRS?
• is there a QRS after every P wave?

Question 24

What happens if SA node and AV nodes fail to generate an impulse to stimulate the ventricles?

Answer 24

Ventricular pacer cells can generate impulses at a rate of 40 bpm or less
-worst case scenario, Purkinje fibers can generate a ventricular rate of 20 bpm

Question 25

Normal Sinus Rhythm (NSR)

Answer 25

when the impulse travels along the normal conduction pathway generated by the SA node

Question 26

Normal Conductive Pathway

Answer 26

SA Node–> AV Node–> Bundle of HIS–> Purkinje fibers

-normal sinus rhythm (NSR)

Question 27

ECG: how many seconds does 1 small box indicate?

Answer 27

0.04 seconds

Question 28

ECG: How many seconds does 5 small boxes indicate?

Answer 28

0.2 seconds

Question 29

ECG: How many seconds does 30 large boxes represent

Answer 29

6 seconds

-3 lines at the top of strip

Question 30

Calculating HR on ECG

Answer 30

• mark off 6 seconds of the strip (30 large boxes)

- count the number of QRS complexes and multiply by 10