JUNCTIONAL ARRHYTHMIAS

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Junctional escape rhythm

A junctional escape rhythm is a string of beats that occurs after a conduction delay from the atria. The normal intrinsic firing rate for cells in the AV junction is 40 to 60 beats/minute.

Remember that the AV junction can take over as the heart’s pacemaker if higher pacemaker sites slow down or fail to fire or conduct. The junctional escape beat is an ex-

ample of this compensatory mechanism. Because junctional escape beats prevent ventricular standstill, they should never be suppressed.

Backward and upside-down

In a junctional escape rhythm, as in all junctional arrhythmias, the atria are depolarized by means of retrograde conduction. The P waves are inverted, and impulse conduction through the ventricles is normal. (See Check age and lifestyle.)

Ages

and stages

Check age and lifestyle

Junctional escape beats may occur in healthy children during sleep. They may also occur in healthy athletic adults. In these situations, no treatment is necessary.

How it happens

A junctional escape rhythm can be caused by any condition that disturbs SA node function or enhances AV junction automaticity. Causes of the arrhythmia include:

•sick sinus syndrome

•vagal stimulation

•digoxin toxicity

•inferior wall MI

•rheumatic heart disease.

The great escape

Whether junctional escape rhythm harms the patient depends on how well the patient’s heart tolerates a decreased heart rate and decreased cardiac output. The less tolerant the heart is, the more significant the effects of the arrhythmia.

What to look for

A junctional escape rhythm shows a regular rhythm of 40 to 60 beats/minute on an ECG strip. Look for inverted P waves in leads II, III, and aVF .

The P waves occur before, after, or hidden within the QRS complex. The PR interval is less than 0.12 second and is measurable only if the P wave comes before the QRS complex. (See

Identifying junctional escape rhythm.)

The rest of the ECG waveform—including the QRS complex, T wave, and QT interval—should appear normal because impulses through the ventricles are usually conducted normally.

Just as junctional escape beats should never be suppressed, neither should escapes to the beach!

urine output. These can occur if the atria are depolarized after the QRS complex, which prevents blood ejection from the atria into the ventricles, or atrial kick.

What to look for

With an accelerated junctional rhythm, look for a regular rhythm and a rate of 60 to 100 beats/minute. (See Identifying accelerated junctional rhythm.) If the P wave is present, it will be inverted in leads II, III, and aVF and will occur before or after the QRS complex or be hidden in it. If the P wave comes before the

QRS complex, the PR interval will be less than 0.12 second. The QRS complex, T wave, and QT interval all appear normal. (See Escape rate higher in young children.)

Low-down, dizzy, and confused

The patient may be asymptomatic because accelerated junctional rhythm has the same rate as sinus rhythm. However, if cardiac output is low, the patient may become dizzy, hypotensive, and confused and have weak peripheral pulses.

Ages

and stages

Escape rate higher in young children

Up to age 3, the atrioventricular nodal escape rhythm is 50 to 80 beats/ minute. Consequently,

a junctional rhythm is considered accelerated in infants and toddlers only when greater than 80 beats/minute.

How you intervene

Treatment for accelerated junctional arrhythmia involves correcting the underlying cause. Nursing interventions include observing the patient to see how well he tolerates this arrhythmia, monitoring his serum digoxin level, and withholding his digoxin dose as ordered.

You should also assess potassium and other electrolyte levels and administer supplements as ordered; monitor vital signs for hemodynamic instability; and observe for signs of decreased cardiac output. Temporary pacing may be necessary if the patient is symptomatic.

Look for a regular

rhythm.

Measurement of the PR interval depends on whether the P wave falls before, in, or after the QRS complex. If it comes before the QRS complex, the only time the PR interval can be measured, it will always be less than 0.12 second.

The QRS complexes look normal, as does the T wave, unless a P wave occurs in it or the rate is so fast that the T wave can’t be detected. (See Junctional and supraventricular tachycardia.)

Rapid rate = instability

Patients with rapid heart rates may have decreased cardiac output and hemodynamic instability. The pulse will be rapid, and dizziness, low blood pressure, and other signs of decreased cardiac output may be present.

How you intervene

The underlying cause should be treated. If the cause is digoxin toxicity, the digoxin should be discontinued. Vagal maneuvers and medications such as verapamil may slow the heart rate for the symptomatic patient. (See Comparing junctional rates.)

If the patient recently had an MI or heart surgery, he may need a temporary pacemaker to reset the heart’s rhythm. A child with a permanent arrhythmia may be resistant to drug therapy and require surgery. The patient with recurrent junctional tachycardia

Comparing junctional rates

The names given to junctional rhythms vary according to rate. The illustration below shows how each rhythm’s name and rate are correlated.

Mixed signals

Junctional and supraventricular tachycardia

If a tachycardia has a narrow QRS complex, you may have trouble deciding whether its source is junctional or atrial. When the rate approaches 150 beats/ minute, a formerly visible P wave is hidden in the previous T wave, so you won’t be able to use the P wave to determine where the rhythm originated.

In these cases, call the rhythm supraventricular tachycardia, a general term that refers to the origin as being above the ventricles. Examples of supraventricular tachycardia include atrial flutter, multifocal atrial tachycardia, and junctional tachycardia.

Look for decreased cardiac output with junctional tachycardia. Boy, am I wiped out!

Accelerated junctional rhythm

Characteristics

•Rhythms: Regular

•Rates: 60 to 100 beats/minute

•P wave: Inverted in leads II, III, and

aVF (if present); occurs before, during, or after QRS complex

•PR interval: Measurable only with P wave that comes before QRS complex; 0.12 second or less

•QRS complex: Normal

•T wave: Normal

•QT interval: Normal

Treatment

•Correction of the underlying cause

•Discontinuation of digoxin if indicated

•Temporary pacemaker insertion if symptomatic

•Junctional tachycardia

Characteristics

•Rhythms: Regular

•Rates: 100 to 200 beats/minute

•P wave: Inverted in leads II, III, aVF; location varies around QRS complex

•PR interval: Shortened at less than

0.12second or unmeasurable

•QRS complex: Normal

•T wave: Usually normal; may contain P wave

•QT interval: Usually normal

Treatment

•Correction of the underlying cause

•Discontinuation of digoxin if indicated

•Temporary or permanent pacemaker insertion if symptomatic

•Vagal maneuvers or drugs such

as verapamil to slow heart rate if symptomatic