6
Junctional arrhythmias
Just the facts
In this chapter, you’ll learn:
the proper way to identify various junctional arrhythmias
the causes, significance, treatment, and nursing implications of each arrhythmia
assessment findings associated with each arrhythmia
interpretation of junctional arrhythmias on an ECG.
A look at junctional arrhythmias
Junctional arrhythmias originate in the atrioventricular (AV) junction—the area around the AV node and the bundle of His. The arrhythmias occur when the sinoatrial (SA) node, a higher pacemaker, is suppressed and fails to conduct impulses or when a block occurs in conduction. Electrical impulses may then be initiated by pacemaker cells in the AV junction.
Just your normal impulse
In normal impulse conduction, the AV node slows transmission of the impulse from the atria to the ventricles, which gives the atria time to contract and pump as much blood as they can into the ventricles before the ventricles contract. However, impulses aren’t always conducted normally. (See Conduction in Wolff- Parkinson-White syndrome, page 112.)
Which way did the impulse go?
Normal impulses keep the blood pumping.
Because the AV junction is located in the lower part of the right atrium near the tricuspid valve, impulses generated in this area
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Now I get it!
Conduction in Wolff-Parkinson-White syndrome
Conduction doesn’t always take place in a normal way. In Wolff-Parkinson-White syndrome, for example, a conduction bypass develops outside the atrioventricular (AV) junction and connects the atria with the ventricles, as shown. Wolff- Parkinson-White syndrome is typically a congenital rhythm disorder that occurs mainly in young children and in adults ages 20 to 35.
Rapidly conducted |
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The bypass formed in Wolff-Parkinson-White |
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syndrome, known as the bundle of Kent, conducts |
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impulses to the atria or the ventricles. Impulses |
Accessory |
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aren’t delayed at the AV node, so conduction is |
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pathway of |
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abnormally fast. Retrograde conduction, circus |
impulse through |
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the bundle of |
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reentry, and reentrant tachycardia can result. |
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Kent |
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Checking the ECG |
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This syndrome causes a shortened PR interval |
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(less than 0.10 second) and a widened QRS com- |
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plex (greater than 0.10 second). The beginning |
Delta wave |
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of the QRS complex may look slurred because of |
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altered ventricular depolarization. This hallmark |
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sign of Wolff-Parkinson-White syndrome is called |
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a delta wave, shown in the inset. |
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When to treat
This syndrome must be treated if tachyarrythmias, such as atrial fibrillation and atrial flutter, occur. First, electrophysiology studies are done to determine the location of the conduction pathway and evaluate specific treatments. Radiofrequency ablation may be used with resistant tachyarrhythmias.
cause the heart to be depolarized in an abnormal way. The impulse moves upward and causes backward, or retrograde, depolarization of the atria and inverted P waves in leads II, III, and aVF, leads in which you would normally see upright P waves. (See Finding the P wave.)
The impulse also moves down toward the ventricles, causing forward, or antegrade, depolarization of the ventricles and an upright QRS complex. Arrhythmias that cause inverted P waves on an ECG may be atrial or junctional in origin.
A LOOK AT JUNCTIONAL ARRHYTHMIAS |
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Mixed signals
Finding the P wave
When the pacemaker fires in the atrioventricular junction, the impulse may reach the atria or the ventricles first. Therefore, the inverted
P wave and the following QRS complex won’t have a consistent relationship. These rhythm strips show the various positions the P wave can take in junctional rhythms.
Atria first
If the atria are depolarized first, the P wave will occur before the QRS complex.
Ventricles first
If the ventricles are depolarized first, the QRS complex will come before the P wave.
Simultaneous
If the ventricles and atria are depolarized simultaneously, the P wave will be hidden in the QRS complex.
Inverted P wave before QRS complex
Inverted P wave before QRS complex
Inverted P wave hidden in QRS complex
Don’t mistake an atrial arrhythmia for a
junctional arrhythmia. Check the PR interval.
Junctional mimic
Atrial arrhythmias are sometimes mistaken for junctional arrhythmias because impulses are generated so low in the atria that they cause retrograde depolarization and inverted P waves. Looking at the PR interval will help you determine whether an arrhythmia is atrial or junctional.
An arrhythmia with an inverted P wave before the QRS complex and a normal PR interval (0.12 to 0.20 second) originated in the atria. An arrhythmia with a PR interval less than 0.12 second originated in the AV junction.
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Premature junctional contraction
A premature junctional contraction (PJC) is a beat that occurs before a normal beat and causes an irregular rhythm. This ectopic beat occurs when an irritable location within the AV junction acts as a pacemaker and fires either prematurely or out of sequence.
As with all beats produced by the AV junction, the atria are depolarized in retrograde fashion, causing an inverted P wave. The ventricles are depolarized normally.
Memory jogger
To help you remember
what a PJC is, think of “beat before” for premature, “normal beat” for junctional, and “causing irregular rhythm” for contraction.
How it happens
PJCs may be caused by toxic levels of digoxin (level greater than 2.5 ng/ml), excessive caffeine intake, inferior wall myocardial infarction (MI), rheumatic heart disease, valvular disease, hypoxia, heart failure, or swelling of the AV junction after heart surgery.
The beat goes on
Although PJCs themselves usually aren’t dangerous, you’ll need to monitor the patient carefully and assess him for other signs of intrinsic pacemaker failure.
What to look for
A PJC appears on a rhythm strip as an early beat causing an irregularity. The rest of the strip may show regular atrial and ventricular rhythms, depending on the patient’s underlying rhythm.
P wave inversion
Look for an inverted P wave in leads II, III, and aVF. Depending on when the impulse occurs, the P wave may fall before, during, or after the QRS complex. (See Identifying a PJC.) If it falls during the QRS complex, it’s hidden. If it comes before the QRS complex, the PR interval is less than 0.12 second.
Because the ventricles are usually depolarized normally, the QRS complex has a normal configuration and a normal duration of less than 0.12 second. The T wave and the QT interval are usually normal.
There's an early beat on the wave form with a
PJC. I prefer it when the beat goes on...
the beat goes on...
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Identifying a PJC
This rhythm strip illustrates premature junctional contraction (PJC). Look for these distinguishing characteristics.
The rhythm is irregular. |
The P wave is inverted with PR |
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interval less than 0.12 second. |
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PJC |
PJC |
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• Rhythm: Irregular atrial and ven- |
• PR interval: 0.14 second for the |
• QT interval: 0.36 second |
tricular rhythms |
underlying rhythm and 0.06 second |
• Other: Pause after PJC |
• Rate: 100 beats/minute |
for the PJC |
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• P wave: Inverted and precedes the |
• QRS complex: 0.06 second |
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QRS complex with PJC; otherwise |
• T wave: Normal configuration |
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normal configuration |
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That quickening feeling
The patient may be asymptomatic or he may complain of palpitations or a feeling of quickening in the chest. You may be able to palpate an irregular pulse. If the PJCs are frequent enough, the patient may have hypotension from a transient decrease in cardiac output.
How you intervene
PJCs usually don’t require treatment unless symptoms occur. In those cases, the underlying cause should be treated. If digoxin toxicity is the culprit, the medication should be discontinued and serum digoxin (Lanoxin) levels monitored.
You should also monitor the patient for hemodynamic instability. If ectopic beats are frequent, the patient should decrease or eliminate his caffeine intake.