5: Junctional rhythms

How do I recognize them?

ECG characteristics of PJCs include the following:

A PJC occurs when an irritable site (i.e., focus) within the AV junction fires before the next SA node impulse is ready to fire, interrupting the underlying rhythm. Because the impulse is conducted through the ventricles in the usual manner, the QRS complex will usually measure 0.11 second or less. PJCs are sometimes called premature junctional extrasystoles. A noncompensatory (incomplete) pause often follows a PJC. This pause represents the delay during which the SA node resets its rhythm for the next beat. PJCs may occur in patterns—couplets, bigeminy, trigeminy, and quadrigeminy.

Junctional complexes may come early or late (i.e., before or after the next expected beat of the underlying rhythm). If the complex is early, it is called a premature junctional complex. If the complex is late, it is called a junctional escape beat. To determine if a complex is early or late, we need to see at least two beats in a row of the underlying rhythm to establish its regularity.

Let’s look at Fig. 5.5. Looking at the overall rhythm, it appears to be irregular. Because the rhythm is irregular, we estimate the rate using the 6-second method of rate calculation at 140 beats/min. All QRS complexes appear to be narrow, so we assume that all impulses started from above the ventricles. Using a pen or pencil, mark an “S” for SA node above each normal-looking P wave. Mark a “J” for junctional above those P waves that are inverted or absent. When you are finished, you should have a “J” marked over the P waves in beats 2, 5, 8, and 11. The rest of the P waves should be marked with an “S.” Now take your calipers or a piece of paper and mark the third and fourth complexes in Fig. 5.5. We already determined that these complexes came from the SA node. These beats reflect the underlying rhythm. We now know that the underlying rhythm is a sinus tachycardia at about 140 beats/min. Now move your calipers or paper to the right. If beat 5 occurred on time (i.e., when the next sinus beat was expected), it would line up with your calipers or paper. The fifth complex is early; it occurred before the next expected sinus beat; therefore, this complex is a PJC. The other beats that have an inverted P wave before the QRS are also PJCs.

A PJC is not an entire rhythm; rather, it is a single beat. When identifying a rhythm, be sure to specify the underlying rhythm and the origin of the ectopic beat(s). In this rhythm strip, we found that the underlying rhythm was a sinus tachycardia at about 140 beats/min. All of the ectopic beats were early and came from the AV junction; therefore, we interpret this rhythm strip as sinus tachycardia at 140 beats/min with frequent PJCs.

What causes them?

PJCs are less common than either PACs or PVCs. Causes of PJCs are shown in Box 5.1.

What do I do about them?

PJCs do not generally require treatment because most individuals who have PJCs are asymptomatic. However, PJCs may lead to symptoms of palpitations or the feeling of skipped beats. Lightheadedness, dizziness, and other signs of decreased cardiac output can occur if PJCs are frequent. If PJCs occur because of ingestion of stimulants or digitalis toxicity, these substances should be withheld.

How do I recognize it?

A junctional escape beat begins in the AV junction and appears late (i.e., after the next expected beat of the underlying rhythm). The ECG characteristics of junctional escape beats include the following:

Junctional escape beats frequently occur during episodes of sinus arrest or follow pauses of nonconducted PACs. Look at Fig. 5.6. Looking at the rhythm strip, you can see that the rhythm is irregular. There are three normal-looking beats on the left and two more on the far right. In the center of the strip is an odd-looking beat that appears in the middle of a long pause between beats 3 and 5. Looking more closely at beats 1, 2, 3, 5, and 6, you can see an upright P wave before each QRS complex. These beats came from the SA node. Based on this information, we know that the underlying rhythm is sinus in origin. Using your calipers or a piece of paper, mark the first and second complexes. When you move the calipers or paper to the right, you can see that beat 4 came late—that is, after the next expected sinus beat.

Now let’s try to figure out where beat 4 came from and why. If you put your finger over beat 4, can you explain what happened? The long pause between beats 3 and 5 is an episode of sinus arrest. Remember that if the SA node fails to initiate an impulse, an escape pacemaker site (i.e., the AV junction or ventricles) should assume responsibility for pacing the heart. Look closely at beat 4. The QRS complex is narrow, and there is no P wave before the QRS complex. The narrow QRS complex and absence of a positive P wave before the QRS complex tell us the beat came from the AV junction. Because the beat is late, it is a junctional escape beat. If beat 4 had been early, we would call it a PJC. What happened here? The SA node fired in beats 1, 2, and 3. When the sinus did not fire again when it should have, the AV junction kicked in and fired. Thus, a junctional escape beat is protective—preventing cardiac standstill. Two sinus beats follow this beat. Complete identification of the events in this rhythm strip would be as follows: Sinus rhythm at 60 beats/min with an episode of sinus arrest and a junctional escape beat.

A junctional rhythm is several sequential junctional escape beats. The terms junctional rhythm and junctional escape rhythm are used interchangeably. Remember that the intrinsic rate of the AV junction is 40 to 60 beats/min. Because a junctional rhythm starts from above the ventricles, the QRS complex is usually narrow, and its rhythm is very regular. The ECG characteristics of a junctional rhythm include the following:

If the AV junction paces the heart at a rate slower than 40 beats/min, the resulting rhythm is called junctional bradycardia. This terminology may seem confusing because the AV junction’s normal pacing rate of 40 to 60 beats/min is bradycardic. However, the term junctional bradycardia refers to a rate slower than expected for the AV junction. A junctional rhythm is shown in Fig. 5.7.

What causes it?

Junctional escape beats frequently occur during episodes of sinus arrest or after pauses of nonconducted PACs. Junctional escape beats may also be observed in healthy individuals during sinus bradycardia. Causes of a junctional rhythm appear in Box 5.2.

What do I do about it?

Patients may be asymptomatic with a junctional escape rhythm, or they may experience signs and symptoms associated with the slow heart rate and decreased cardiac output. Signs and symptoms may include lightheadedness, weakness, chest pain or pressure, syncope, altered mental status, effort intolerance, and hypotension. If the patient is experiencing symptoms, try to determine their frequency, timing, duration, severity, longevity, circumstances, triggers, and alleviating factors. Be sure to ask about any prescribed and over-the-counter medications (including herbal supplements) that the patient may be taking because these agents can cause or worsen a bradycardia.

Treatment depends on the cause of the dysrhythmia, the patient’s presenting signs and symptoms, and the frequency and severity of those symptoms. Patients who experience frequent symptoms may be asked to undergo continuous ambulatory ECG monitoring to determine if a dysrhythmia is a precipitating cause. Laboratory tests (e.g., electrolytes, thyroid function) may be ordered to help identify the cause of the dysrhythmia.

If a junctional rhythm results from the effects of a medication that slows the sinus rate, the medication should be withheld to allow the SA node to resume its pacing function. When a patient experiences serious signs and symptoms related to a slow heart rate, treatment should include applying a pulse oximeter, administering supplemental oxygen (if indicated), establishing intravenous (IV) access, and obtaining a 12-lead ECG. Atropine, given IV, is the first medication given for symptomatic bradycardia (Kusumoto et al., 2018). Reassess the patient’s response and continue monitoring. Implantation of a permanent pacemaker may be necessary if the patient is symptomatic and the junctional rhythm is the result of sinus node dysfunction.

How do I recognize it?

If the AV junction speeds up and fires at 61 to 100 beats/min, the resulting rhythm is called an accelerated junctional rhythm. This rhythm is caused by altered automaticity of the bundle of His. The only ECG difference between a junctional rhythm and an accelerated junctional rhythm is the increase in the ventricular rate. An example of an accelerated junctional rhythm is shown in Fig. 5.8. The ECG characteristics of this rhythm include the following:

What causes it?

An accelerated junctional rhythm is associated with altered automaticity or triggered activity (Page et al., 2016). Causes of this dysrhythmia include acute MI, cardiac surgery, chronic obstructive pulmonary disease, digitalis toxicity, hypokalemia, and rheumatic fever. It may also be observed transiently after ablation for AV nodal reentrant tachycardia.

What do I do about it?

The patient is usually asymptomatic because the ventricular rate is 61 to 100 beats/min; however, the patient should be monitored closely. If the patient is symptomatic, treatment is focused on addressing the underlying cause of the dysrhythmia. For example, if the rhythm is caused by digitalis toxicity, this medication should be withheld.

How do I recognize it?

Junctional tachycardia is an ectopic rhythm that begins in the pacemaker cells found in the bundle of His. A junctional tachycardia exists when three or more sequential PJCs occur at a rate of more than 100 beats/min. ECG characteristics of junctional tachycardia include the following:

Junctional tachycardias are usually regular but may be irregular with variable conduction to the atria (Page et al., 2016). Nonparoxysmal (i.e., gradual onset) junctional tachycardia is a benign dysrhythmia that is usually associated with a gradual increase in rate (i.e., a warm-up pattern) to more than 100 beats/min; it rarely exceeds 120 beats/min (Zimetbaum, 2020). Paroxysmal junctional tachycardia, which is also known as focal or automatic junctional tachycardia, is an uncommon dysrhythmia that starts and ends suddenly and is often precipitated by a PJC. The ventricular rate for paroxysmal junctional tachycardia is generally faster, at a rate of 140 beats/min or more. When the ventricular rate is faster than 150 beats/min, it is challenging to distinguish junctional tachycardia from other supraventricular tachycardias. An example of junctional tachycardia is shown in Fig. 5.9.

What causes it?

Junctional tachycardia is caused by a disorder of impulse formation (i.e., automaticity) (Miller et al., 2019). It is uncommon in adults but may occur because of an acute coronary syndrome, digitalis toxicity, heart failure, or theophylline administration. Junctional tachycardia is more often seen in infants after cardiac surgery for congenital heart disease (Page et al., 2016).

What do I do about it?

Patients experiencing a junctional tachycardia may be asymptomatic. With sustained ventricular rates of 150 beats/min or more, the patient may complain of fatigue, palpitations, or chest discomfort or may experience syncope. Because of the fast ventricular rate, the ventricles may be unable to fill completely, resulting in decreased cardiac output. The more rapid the rate, the greater the incidence of symptoms because of increased myocardial oxygen demand. Junctional tachycardia associated with an acute coronary syndrome may do the following:

Treatment depends on the severity of the patient’s signs and symptoms, and expert consultation is advised. If the patient tolerates the rhythm, observation is often all that is needed. If the patient is symptomatic because of the rapid rate, initial treatment should include applying a pulse oximeter, administering supplemental oxygen (if indicated), establishing IV access, and obtaining a 12-lead ECG. Because it is often difficult to distinguish junctional tachycardia from other narrow-QRS tachycardias, vagal maneuvers and, if necessary, IV adenosine may be ordered to help determine the origin of the rhythm. If the rhythm is the result of digitalis toxicity, the medication should be withheld. If the rhythm is the result of theophylline administration, the infusion should be slowed or stopped. A beta-blocker (e.g., propranolol) or calcium blocker (e.g., diltiazem, verapamil) may be ordered (if no contraindications exist) to slow conduction through the AV node and thereby slow the ventricular rate. Synchronized cardioversion is not indicated for junctional tachycardia because it typically recurs within seconds after the shock, and a release of endogenous catecholamines following the shock can worsen the dysrhythmia (Miller et al., 2019). A summary of junctional rhythm characteristics appears in Table 5.1.

Questions 8—10 pertain to the following scenario

A 63-year-old man is complaining of dizziness that began about 45 minutes ago while cleaning his garage. Because the patient’s oxygen saturation level on room air was 88%, supplemental oxygen is being administered. The cardiac monitor has been applied, revealing the rhythm in Fig. 5.10. A coworker is attempting to establish intravenous access.

Junctional rhythms—practice rhythm strips

Use the five steps of rhythm interpretation to interpret each of the following rhythm strips. All rhythms were recorded in lead II unless otherwise noted.

Practice rhythm strip answers

Note: The rate and interval measurements provided here were obtained using electronic calipers.