where do PJCs originate from?
junctional tissue
when do PJCs occur?
when junctional cell fires earlier than expected
3 key points r/t atrial depolarization and P waves from a PJC
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
how can P waves of a PJC appear?
- inverted
- after a QRS complex
- hidden in QRS complex or not seen
where does depolarization start?
in AV junction and proceeds from here
how does the location of the P wave impact the PR interval?
- 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
what are 2 reasons why a P wave in a junctional rhythm is not seen?
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
O2 supply and demand implications for PJCs
- 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
characteristics of PJC
- rate
- rhythm
- P wave
- PR interval
- QRS complex
- 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
cause of PJCs
- stimulants (alcohol, coffee, tobacco)
- hypoxia
- electrolyte imbalances
- ischemia
- cardiomyopathy
- less common than PACs and PVCs, likely to be associated with cardiac disease
intervention for PJCs
assess pt (ABCs), check electrolytes (K+, Mg+, Ca+), call doctor if concerned
what is the pacemaker site for junctional escape rhythm?
secondary pacemaker site in AV junction because SA node fails
what is the inherent rate of firing of the junctional pacemaker site and what is the rhythm?
40-60x/min and rhythm is regular
what would be the rate of firing for accelerated junctional rhythm?
60-100x/min
compare JER to PJC
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
O2 supply and demand implications for JER
- decreased HR = decreased CO
- inverted or no P waves = retrograde or non-depolarization of atria = decreased/loss of atrial kick and CO
characteristics of JER
- P wave
- PRI
- QRS complex
- conduction problem
- 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
causes of JER
myocardial ischemia, drug toxicity, hypoxia
intervention for JER
assess pt (ABCs), if CO is compromised atropine may be indicated. If pt unresponsive to atropine, temporary pacemaker may be needed
what is the HR and pacemaker site in accelerated junctional rhythm?
60-100bpm; AV junction = pacemaker
what is junctional tachycardia caused by?
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
what is the rate of firing in junctional tachycardia?
> 100bpm
O2 supply and demand implications for junctional tachycardia
- 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
characteristics of junctional tachycardia
- rate
- rhythm
- P wave
- PRI
- QRS complex
- conduction problem
- 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
