Cardiac Conduction Disorders: Rhythm and Rate

Question 1

Manifested by multiple P wave shapes and PR intervals

Answer 1

wandering pacemaker

Question 2

Describe SA node beats

Answer 2

smooth upright P waves

Question 3

Describe non-SA node beats

Answer 3

flattened, notched, biphasic (S-shaped) or inverted P waves

Question 4

Wandering pacemaker: ________ contraction is normal, so the QRS complex is ______ width and height

Answer 4

Wandering pacemaker: ventricular contraction is normal, so the QRS complex is normal width and height

Question 5

What may precipitate a wandering pacemaker

Answer 5

reduced SA node firing

Question 6

Most common in very young, very old, athletes, rarely causes symptoms or requires treatment

Answer 6

wandering pacemaker

Question 7

EKG characteristics of wandering pacemaker

Answer 7

• rate <100
• P wave shape varies
• Irregular ventricular rhythm

Question 8

Occurs when tachycardia occurs at the same time as wandering pacemaker

Answer 8

multifocal atrial tachycardia

Question 9

EKG characteristics of multifocal atrial tachycardia

Answer 9

• rate >100
• P wave shape varies
• Irregular ventricular rhythm

Question 10

Caused by very rapidly firing ectopic atrial foci

Answer 10

atrial fibrillation

Question 11

What does very rapidly firing ectopic atrial foci result in?

Answer 11

results in uncoordinated, ineffective, irregular atrial contraction

Question 12

What is the irregular atrial contraction due to?

Answer 12

due to occasional impulses resulting in AV node discharge

Question 13

How long does atrial fibrillation last?

Answer 13

may occur suddenly and last for minutes to days OR be permanent

Question 14

EKG characteristics of atrial fibrillation

Answer 14

• P waves absent
• usually normal QRS width
• Irregularly irregular rhythm
• continuous chaotic atrial spikes

Question 15

occur after the controlling automaticity focus (usually the SA node) stops pacing (“sinus arrest”)

Answer 15

escape rhythms

Question 16

occurs when a transient pacer escape occurs and resumes after one beat

Answer 16

escape beat

Question 17

occurs when the SA node stops firing

Answer 17

sinus arrest

Question 18

occurs when another atrial pacer takes over the rhythm

Answer 18

atrial escape rhythm

Question 19

EKG change with atrial escape rhythm

Answer 19

• different P wave

- same QRS

Question 20

Occurs when the AV node (or a nearby focus) takes over following sinus arrest

Answer 20

junctional escape rhythm

Question 21

EKG change with junctional escape rhythm

Answer 21

• loss of P wave (buried in another wave) OR P wave may occur before or after QRS wave
• unusual P wave shape
• QRS complex usually unchanged

Question 22

Occurs when pacing fails to occur from more superior pacers (e.g., SA, AV) and automaticity foci in the ventricles take over

Answer 22

ventricular escape rhythm

Question 23

EKG change with ventricular escape rhythm

Answer 23

• loss of P wave or P wave not conducting

- wide QRS complex

Question 24

What do ventricular escape rhythms usually result from?

Answer 24

ventricular automaticity focus activation

Question 25

Following sinus ____ (or block) another _____ will take over, resulting in an ______ _____.

Answer 25

Following sinus arrest (or block) another pacer will take over, resulting in an escape beat.

Question 26

originate early from an “irritable” automaticity focus

Answer 26

premature beats

Question 27

Causes of atrial and junctional focus irritability include:

Answer 27

- Epinephrine - Sympathetic stimulation - B1 stimulants (caffeine, amphetamines, cocaine) - Drugs (excess digitalis, ethanol) - Hyperthyroidism - Cardiac stretch (heart failure) - Low oxygen

Question 28

Which automaticity foci are particularly susceptible to low oxygen tension, hypokalemia, excess stretch, etc?

Answer 28

ventricular automaticity foci

Question 29

usually result in a change in rhythm (shortened) followed by a prolonged period after which the SA node resets and takes over

Answer 29

premature atrial beats/contraction (PAB, PAC)

Question 30

EKG change with premature atrial beats

Answer 30

-different shaped P wave with normal QRS wave

Question 31

arise from an irritable atrial focus, causing premature atrial depolarization

Answer 31

premature atrial beats

Question 32

What are some other EKG changes that may result from premature atrial beats?

Answer 32

- May result in aberrant ventricular conduction if one bundle branch has not repolarized fully (wide QRS) - If AV node does not conduct the PAB, a QRS complex is absent

Question 33

occurs when each normal beat is followed by an abnormal PAB

Answer 33

atrial bigeminy

Question 34

occurs when two normal beats are followed by an abnormal PAB

Answer 34

atrial trigeminy

Question 35

Premature beats may originate at an irritable automaticity focus in the AV node (junction), resulting in what?

Answer 35

premature junctional beat

Question 36

EKG changes with premature junctional beat

Answer 36

- Occur prematurely – early - P waves may be buried in the QRS wave, occur before or after, or not be conducted - The QRS complex may be normal, or wider than normal due to incompletely repolarized bundle branches

Question 37

result when an irritable ventricular automaticity focus fires unexpectedly

Answer 37

premature ventricular contractions

Question 38

EKG changes with premature ventricular contractions

Answer 38

- Occur prematurely - No P wave - The impulse is slowly transmitted to the rest of the ventricles through the myocardium, producing a wide QRS wave and bizarre T wave

Question 39

Why does it take a long time for full depolarization to cure with premature ventricular beats?

Answer 39

Because the ventricular wall conducts slowly (via cardiomyocyte conduction rather than through the conduction system)

Question 40

What does the shape of the wave depend on for premature ventricular beats?

Answer 40

The shape of the wave will depend on where the depolarization begins

Question 41

What generally follows a PVC? Why?

Answer 41

there is generally a compensatory pause as the ventricles repolarize

Question 42

Why might there be P waves occurring with PVC?

Answer 42

There may be P waves occurring from independent atrial depolarization

Question 43

Why might multiple PVCs may occur?

Answer 43

if the ventricular automaticity focus is very irritable (e.g., poor oxygenation, epinephrine, β-agonists)

Question 44

What may multiple PVCs result in?

Answer 44

- ventricular bigeminy - ventricular trigeminy - ventricular tachycardia

Question 45

If all PVCs originate from the same ____ the QRS waves will have the same _____.

Answer 45

If all PVCs originate from the same focus the QRS waves will have the same shape.

Question 46

If the PVCs originate from _____ foci the ____ waves will look different.

Answer 46

If the PVCs originate from multiple foci the QRS waves will look different.