Junctional Beats: Premature Junctional Contraction and Junctional Rhythm

Junctional rhythms originate from the atrioventricular (AV) junction, which is located near the AV node and the bundle of His, rather than from the sinoatrial (SA) node.¹⁹⁸ These rhythms can manifest as premature junctional contractions (PJCs) or a sustained junctional rhythm.¹⁹⁸

Analogy: “A section of the orchestra taking the lead when the usual conductor falters.”

ECG Characteristics

Premature junctional contractions (PJCs) on an ECG are characterized by a QRS complex that occurs prematurely. The P wave associated with a PJC may be absent if the atria and ventricles depolarize simultaneously, inverted (negative in leads II, III, aVF) if the atria are depolarized retrogradely (backwards), or it may occur after the QRS complex.¹⁹⁸ If a retrograde P wave precedes the QRS complex, the PR interval will be short, typically less than 0.12 seconds.¹⁹⁸ The QRS complex is usually narrow, as ventricular depolarization occurs via the normal pathways.¹⁹⁸ However, it can be aberrant (conducted abnormally) if the beat is very premature.¹⁹⁸ Junctional rhythm occurs when the AV junction becomes the primary pacemaker of the heart. On the ECG, junctional rhythm is regular.²⁰⁰ The heart rate depends on the specific type of junctional rhythm: junctional escape rhythm (40-60 bpm), accelerated junctional rhythm (60-100 bpm), and junctional tachycardia (greater than 100 bpm).²⁰⁰ The P waves in a junctional rhythm will have the same characteristics as in PJCs.

Other Symptoms

Premature junctional contractions (PJCs) may be felt as palpitations or a skipped beat.¹⁹⁸ Junctional rhythm may be asymptomatic, particularly if the heart rate is within the normal range. However, slower junctional rhythms can lead to symptoms such as fatigue, dizziness, lightheadedness, or syncope.¹⁹⁹ Junctional rhythms can be caused by conditions such as digitalis toxicity, excessive caffeine intake, coronary artery disease, or inflammation of the heart.¹⁹⁹

Analogy

“Like a backup conductor stepping in, the AV junction initiates the heartbeat.”