Junctional Rhythms

Question 1

where do PJCs originate from?

Answer 1

junctional tissue

Question 2

when do PJCs occur?

Answer 2

when junctional cell fires earlier than expected

Question 3

3 key points r/t atrial depolarization and P waves from a PJC

Answer 3

1) P wave still represents atrial depolarization, but that signal did not originate from the SA node. the cells of the SA node did not depolarize as they would have in NSR

2) impulses arising in AV junction can create atrial depolarization if the electrical signals travel backward from the AV junction into the atria

3) P waves associated with junctional rhythms can occur in different shapes or may be hidden in other parts of ECG

Question 4

how can P waves of a PJC appear?

Answer 4

• inverted
• after a QRS complex
• hidden in QRS complex or not seen

Question 5

where does depolarization start?

Answer 5

in AV junction and proceeds from here

Question 6

how does the location of the P wave impact the PR interval?

Answer 6

• if P wave precedes QRS complex, PRI is typically <0.12 seconds
• shortened PRI r/t shortened distance the electrical impulse needs to travel from the AV junction to the atria
• ventricles depolarize normally so QRS looks normal

Question 7

what are 2 reasons why a P wave in a junctional rhythm is not seen?

Answer 7

1) impulse generated by AV junction is blocked from going back into atrium; there is no P wave and no atrial depolarization
2) the P wave is buried in the QRS complex b/c the magnitude of the QRS is greater than the P wave

Question 8

O2 supply and demand implications for PJCs

Answer 8

• impact on CO and O2 supply varies on frequency of PJC
• atrial kick is decreased, esp when atria are depolarized after ventricles
• frequent PJCs = increased HR = increased O2 demand

Question 9

characteristics of PJC
- rate
- rhythm
- P wave
- PR interval
- QRS complex

Answer 9

• rate = normal but depends on # of PJCs occurring
• rhythm = underlying regular but appears irregular d/t PJCs
• P wave = inverted before QRS; blocked or buried in QRS and not seen; or after QRS
• PR interval = not measurable if no P wave before QRS
• QRS = 0.10 sec or less

Question 10

cause of PJCs

Answer 10

• stimulants (alcohol, coffee, tobacco)
• hypoxia
• electrolyte imbalances
• ischemia
• cardiomyopathy
• less common than PACs and PVCs, likely to be associated with cardiac disease

Question 11

intervention for PJCs

Answer 11

assess pt (ABCs), check electrolytes (K+, Mg+, Ca+), call doctor if concerned

Question 12

what is the pacemaker site for junctional escape rhythm?

Answer 12

secondary pacemaker site in AV junction because SA node fails

Question 13

what is the inherent rate of firing of the junctional pacemaker site and what is the rhythm?

Answer 13

40-60x/min and rhythm is regular

Question 14

what would be the rate of firing for accelerated junctional rhythm?

Answer 14

60-100x/min

Question 15

compare JER to PJC

Answer 15

PJCs are single impulses or a cluster of impulses initiated by junctional tissue resulting in junctional beats in the predominant sinus rhythm, whereas JERs are the predominant rhythm

Question 16

O2 supply and demand implications for JER

Answer 16

• decreased HR = decreased CO
• inverted or no P waves = retrograde or non-depolarization of atria = decreased/loss of atrial kick and CO

Question 17

characteristics of JER
- P wave
- PRI
- QRS complex
- conduction problem

Answer 17

• P wave = maybe inverted before QRS, buried in QRS, or appear after
• PRI = if present, can be measured and recorded; 0.12 sec or less
• QRS complex = 0.10 sec or less
• Conduction problem = impulse at AV junction who’s intrinsic rate is slower than SA node

Question 18

causes of JER

Answer 18

myocardial ischemia, drug toxicity, hypoxia

Question 19

intervention for JER

Answer 19

assess pt (ABCs), if CO is compromised atropine may be indicated. If pt unresponsive to atropine, temporary pacemaker may be needed

Question 20

what is the HR and pacemaker site in accelerated junctional rhythm?

Answer 20

60-100bpm; AV junction = pacemaker

Question 21

what is junctional tachycardia caused by?

Answer 21

irritable focus in AV junction which speeds up and overrides the SA node for control of heart rhythm; atria are depolarized in a retrograde fashion

Question 22

what is the rate of firing in junctional tachycardia?

Answer 22

> 100bpm

Question 23

O2 supply and demand implications for junctional tachycardia

Answer 23

• decrease in atrial kick decreases CO by up to 30% d/t retrograde P waves or non-depolarization of atria
• increase HR = decreases ventricular filling time, CPT, CO; increase myocardial O2 demand

Question 24

characteristics of junctional tachycardia
- rate
- rhythm
- P wave
- PRI
- QRS complex
- conduction problem

Answer 24

• rate: >100bpm
• rhythm: regular
• P wave: inverted before QRS, hidden in QRS, or after QRS
• PRI: if present before QRS, < 0.12 sec
• QRS complex: 0.10 sec or less
• Conduction problem: impulse formation is at AV junction at rate >100bpm

Question 25

causes of junctional tachycardia

Answer 25

failure of SA node, AV junction takes over pacing. heart disease and variety of drugs

Question 26

interventions for junctional tachycardia

Answer 26

check pt (ABCs), treat cause (ie. revascularize if MI). If degree of compromise is not dramatic = pharmacological intervention. If pt is seriously compromised, urgent electrical therapy or cardioversion