Causes of Junctional Rhythm
Junctional rhythm is primarily caused by enhanced automaticity from an ectopic focus in the AV junction, most commonly triggered by digoxin toxicity, myocardial infarction/ischemia, or electrolyte abnormalities (particularly hypokalemia). 1, 2
Mechanism
The underlying mechanism involves enhanced (abnormal) automaticity or triggered activity arising from the AV node or His bundle region. 1 This occurs when the normal sinus node either fails to generate impulses adequately or when the AV junctional tissue develops increased automaticity that supersedes the sinus rate. 1, 2
Primary Causes
Most Common Etiologies
Digoxin toxicity is the most frequently cited cause of nonparoxysmal junctional tachycardia in adults, occurring at rates of 70-130 bpm. 1, 2 The FDA label specifically warns that digoxin overdose can manifest as symptomatic bradyarrhythmias requiring withdrawal of the drug. 3
Myocardial infarction and ischemia are major causes due to altered automaticity in the AV nodal region. 1, 2
Hypokalemia is a critical electrolyte disturbance that precipitates junctional rhythm, particularly in the setting of digoxin use. 1, 2, 3
Additional Underlying Conditions
Post-cardiac surgery state, especially in infants and children after congenital heart surgery (junctional ectopic tachycardia). 1, 2
Chronic obstructive lung disease with hypoxia can trigger enhanced automaticity in the AV junction. 1, 2
Inflammatory myocarditis causes junctional rhythm through inflammation affecting the conduction system. 1, 2
Sinus node dysfunction may allow the AV junction to become the dominant pacemaker when sympathetic stimulation increases junctional automaticity beyond the failing sinus rate. 1, 2
Hyperkalemia can present with junctional rhythm, though this is a less common manifestation. 4
Clinical Context and Types
Nonparoxysmal Junctional Tachycardia (More Common in Adults)
This benign form occurs at 70-120 bpm with characteristic "warm-up" and "cool-down" patterns that cannot be terminated by pacing. 1 The mechanism is enhanced automaticity or triggered activity rather than reentry. 1
Focal Junctional Tachycardia (Rare in Adults)
This presents at 120-220 bpm and is typically exercise or stress-related, occurring in structurally normal hearts or with congenital abnormalities. 1, 2 The mechanism is enhanced abnormal automaticity from an ectopic focus in the AV junction. 1
Critical Clinical Pitfall
The most important feature is that junctional rhythm may be a marker for serious underlying conditions requiring immediate attention. 1, 2 Do not simply treat the rhythm—aggressively search for and correct the underlying cause:
- Immediately check digoxin levels if the patient is on this medication. 1, 2, 3
- Obtain serum potassium and magnesium levels urgently. 1, 2, 3
- Evaluate for acute myocardial ischemia with troponins and ECG. 1, 2
- Consider recent cardiac surgery as a precipitant. 1, 2
Management Principle
Treatment centers on addressing the underlying condition rather than the rhythm itself. 1 Withholding digoxin when toxicity is suspected is usually adequate unless ventricular arrhythmias or high-grade heart block develop, which may require digoxin-binding agents. 1, 3