Week 2 - Junctional Rhythms

What structures make up the AV junction?

The AV node + non-branching portion of the Bundle of His.

What is the AV node's main electrical function?

It delays the impulse, allowing the atria to finish contracting and fill the ventricles before ventricular contraction.

What does the Bundle of His do?

Connects the AV node → bundle branches and conducts the impulse toward the ventricles.

When can the AV junction take over as the heart's pacemaker?

When:

1. SA node fails to fire

2. SA node fires slower than the junction

3. SA impulse occurs but doesn't reach the ventricles

Why are P waves abnormal in junctional rhythms?

Because the impulse originates near the AV junction and travels backward (retrograde) through the atria.

Where can the P wave appear in a junctional beat? Why?

Before, hidden within, or after the QRS.

The junctional impulse travels toward the atria and ventricles, and the relative timing determines where atrial depolarization appears.

If a junctional P wave is visible, what does it usually look like?

Inverted, especially in II, III, and aVF.

What is the typical QRS width of a junctional beat?

Usually <0.12 sec unless aberrantly conducted.

If the junctional P wave occurs BEFORE the QRS, what is the expected PR Interval?

Usually ≤0.12 sec

Why is the PR Interval short in a junctional beat when the P comes before the QRS?

The impulse originates close to the ventricles, so there is less conduction distance/time between atrial and ventricular depolarization.

List all Junctional Rhythms (5)

1. Junctional Bradycardia

2. Junctional Escape Rhythm

3. Accelerated Junctional Rhythm

4. Junctional Tachycardia

5. Premature Junctional Complex (PJC)

PJC — Define

Premature Junctional Complex — An early, extra heartbeat that starts in the atrioventricular (AV) junction of the heart instead of the normal sinus node.

PJC — are they rhythms?

No. It is an ectopic complex/beat occurring within an underlying rhythm.

PJC — How to identify a rhythm containing a PJC?

Name the underlying rhythm + the PJCs.

eg. “Sinus rhythm at 98 bpm with 2 PJCs.”

PJC — how to distinguish PJC from Junctional Escape Beat

PJC = EARLY
Escape beat = LATE

PJC — what happens to rhythm regularity when PJCs occur?

It becomes irregular because the PJCs occur prematurely.

PJC — P wave findings

P wave may be:

• Absent/hidden

• Inverted before QRS

• Inverted after QRS

PJC — What type of pause follows a PJC? Why?

Non-compensatory (incomplete) pause.

The PJC can reset the SA node, altering the timing of the next sinus beat.

What is Junctional Bigeminy?

Every 2nd beat is a PJC.

Normal → PJC → Normal → PJC

What is Junctional Trigeminy?

Every 3rd beat is a PJC.

Normal → Normal → PJC

PJC — Causes (8)

• CHF

• Acute coronary syndromes

• Mental/physical fatigue

• Valvular heart disease

• Digitalis toxicity

• Electrolyte imbalance

• Rheumatic heart disease

• Stimulants such as caffeine/tobacco

PJC — Patient presentation

Usually asymptomatic, although they may report palpitations or “skipped beats.”

Junctional Escape Beat — Define

A sustained rhythm in which the AV junction becomes the pacemaker.

Junctional Escape Beat — Characteristics

Rate:

Rhythm:

P Wave:

Rate: 40–60 bpm

Rhythm: Regular

P Wave: inverted before, during, or inverted after QRS

How are junctional rhythms classified by rate?

<40 bpm:

40—60 bpm:

60—100 bpm:

>100 bpm:

<40 bpm: Junctional Bradycardia

40—60 bpm: Junctional Escape Rhythm

60—100 bpm: Accelerated Junctional Rhythm

>100 bpm: Junctional Tachycardia

Accelerated Junctional Rhythm — Define

A junctional rhythm with a rate of 60–100 bpm.

Accelerated Junctional Rhythm — Differentiate from junctional escape rhythm

Primarily the rate:

Escape = 40–60
Accelerated = 60–100

Junctional Tachycardia — Define

A rapid rhythm originating from the AV junction, generally >100 bpm.

Junctional Tachycardia — Types

Non-paroxysmal and paroxysmal junctional tachycardia.

Junctional Tachycardia (Non-Paroxysmal) — How does it begin

Usually begins as accelerated junctional rhythm and the HR gradually increases >100 bpm.

Junctional Tachycardia (Non-Paroxysmal) — associated ventricular rate

Approximately 101–140 bpm

Junctional Tachycardia (Paroxysmal) — How does it begin & End

Suddenly

Junctional Tachycardia (Paroxysmal) — What can precipitate it

PJC — Premature Junctional Complex

Junctional Tachycardia (Paroxysmal) — associated ventricular rate

Generally >140 bpm.

What is the key onset difference between non-paroxysmal and paroxysmal junctional tachycardia?

Non-paroxysmal: gradual acceleration
Paroxysmal: sudden start/stop

At >150 bpm, can you reliably distinguish junctional tachycardia from SVT based on the ECG?

NO

Junctional Tachycardia — Causes (6)

• Digitalis toxicity

• Acute MI

• Cardiac surgery

• Rheumatic fever

• COPD

• Hypokalemia

Junctional Tachycardia — Why is it dangerous for patients with acute coronary syndrome?

The faster rate increases myocardial O₂ consumption, potentially worsening ischemia.

Junctional Tachycardia — what complications can it contribute to in ACS?

• Increased ischemia / MI size

• Increased chest pain

• CHF

• Decreased BP

• Cardiogenic shock

• Ventricular dysrhythmias (VT/VF)