1. Introduction

Accelerated junctional rhythm (AJR) is a non-sinus rhythm in which an impulse arising in the atrioventricular (AV) junction discharges faster than the sinus node and takes over ventricular activation. It is generally classified by a ventricular rate of 60–100 beats/min. The rhythm reflects enhanced junctional automaticity, reduced sinus-node automaticity, or a combination of both.

AJR is often encountered in the setting of drug effects (classically digoxin toxicity), myocardial ischaemia, myocarditis, or after cardiac surgery. Recognition matters because the ECG pattern itself may be relatively well tolerated, while the underlying trigger may require prompt investigation and treatment.

2. Electrophysiology and pathophysiology

Under normal conditions, the sinoatrial (SA) node is the dominant pacemaker. Its faster spontaneous depolarization suppresses subsidiary pacemakers through overdrive suppression. Junctional pacemaker tissue around the AV node and His bundle can generate impulses independently, but is ordinarily not the dominant source of activation.

AJR occurs when junctional automaticity increases and/or sinus-node automaticity falls sufficiently for the junctional focus to exceed the sinus rate. The junctional impulse activates the ventricles through the His–Purkinje system, usually producing a narrow QRS complex. Atrial activation may proceed retrogradely from the junction, producing inverted P waves in the inferior leads; the P wave may occur before, within, or after the QRS depending on the timing of retrograde atrial activation.

When atrial and ventricular activity are not consistently linked, AV dissociation may be present. In this setting, the ventricular rate is often greater than the independent atrial rate. AV dissociation is a relationship between chambers, not by itself proof of complete AV block.

3. Characteristic ECG features

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4. Systematic ECG interpretation

1. Confirm the ventricular rate. Calculate the rate from the R–R intervals. A rate in the 60–100 bpm range is compatible with AJR but is not diagnostic on its own.
2. Assess QRS width and morphology. A narrow QRS supports activation through the normal His–Purkinje system. If wide, compare with a baseline ECG and consider bundle branch block, aberrancy, pre-excitation, or a ventricular rhythm.
3. Search carefully for P waves. Inspect inferior leads and V1. Look immediately before, within, and after each QRS for retrograde atrial activity.
4. Determine the P–QRS relationship. A consistent short PR with inverted inferior P waves supports retrograde conduction. Independent P waves with no fixed relationship indicate AV dissociation.
5. Compare atrial and ventricular rates. If AV dissociation is present, determine which chamber is faster and whether capture or fusion beats are present.
6. Look for the cause. Review digoxin and other medications, recent surgery, ischaemic symptoms, myocarditis, and metabolic or electrolyte abnormalities.
7. Correlate clinically. Assess blood pressure, perfusion, symptoms, and evidence of acute myocardial injury or drug toxicity before deciding whether the rhythm itself needs intervention.

5. Diagnostic criteria and rate classification

The supplied reference classifies junctional rhythms by ventricular rate. These ranges are conventional descriptive categories, not a stand-alone diagnostic test. The junctional origin must be supported by the ECG morphology and atrioventricular relationship.

Essential and supportive evidence

• Essential reasoning: a rhythm consistent with an AV-junctional pacemaker that is faster than the sinus pacemaker.
• Supportive ECG findings: ventricular rate around 60–100 bpm, usually narrow QRS, absent or retrograde P waves, and possible AV dissociation.
• Important limitation: retrograde P waves are not obligatory, and a narrow QRS does not by itself establish the site of origin.

6. Differential diagnosis

Practical distinction from AIVR: if the QRS is wide, do not assume aberrant AJR. Look for capture and fusion beats, compare with baseline conduction, and assess the clinical setting. Their presence indicates competing ventricular and supraventricular activation and favours a ventricular focus.

Practical distinction from re-entry: abrupt onset/termination and a highly stereotyped tachycardia favour re-entry; variability or gradual rate changes can support automaticity, but these clues are not definitive. Response to vagal manoeuvres should not be used as a sole diagnostic test.

7. Clinical significance

AJR may be transient and well tolerated, particularly when the ventricular rate is modest and the underlying cause is reversible. Its clinical importance is determined by the cause, the adequacy of cardiac output, and the degree of AV synchrony.

• Loss of atrial contribution: retrograde or dissociated atrial activation can reduce effective atrial contribution to ventricular filling, which may be important in patients with diastolic dysfunction or limited haemodynamic reserve.
• Underlying myocardial disease: ischaemia, myocarditis, or postoperative conduction-system disturbance may be more consequential than the rhythm label itself.
• Drug toxicity: AJR in a patient taking digoxin should prompt a focused assessment for digitalis toxicity, especially when accompanied by gastrointestinal, neurological, visual, or additional arrhythmic manifestations.
• Persistent symptoms: dizziness, presyncope, syncope, dyspnoea, chest discomfort, or hypotension require clinical evaluation rather than reassurance based solely on the rate.

9. Clinical evaluation and management principles

Initial assessment

• Assess airway, breathing, circulation, blood pressure, oxygenation, mental status, perfusion, and symptoms.
• Obtain a 12-lead ECG and compare with previous tracings; use continuous monitoring when clinically indicated.
• Review medication exposure and recent dose changes, especially digoxin, beta-agonists, and other agents affecting automaticity or conduction.
• Investigate the suspected trigger: electrolytes (including potassium and magnesium), renal function, ischaemia evaluation, and other tests guided by clinical context. If digoxin exposure is relevant, assess serum concentration with attention to timing and the overall clinical picture.

Treatment approach

• Stable and asymptomatic: observation and correction of the precipitating cause may be sufficient. A rhythm that is maintaining ventricular rate should not be suppressed reflexively.
• Medication-related: withhold or adjust the suspected offending agent as clinically appropriate and manage toxicity according to established toxicology guidance. Life-threatening digoxin toxicity warrants urgent consideration of digoxin-specific antibody fragments.
• Ischaemia or inflammation: treat the underlying disease and monitor for associated conduction or ventricular arrhythmias.
• Symptomatic or haemodynamically significant rhythm: seek expert input and manage the underlying mechanism and instability. Pacing decisions should be based on associated sinus-node disease, high-grade AV block, or persistent clinically significant bradycardia—not the AJR label alone.
• Persistent or atypical tachyarrhythmia: obtain cardiology/electrophysiology review when the mechanism is uncertain or a re-entrant tachycardia remains possible.

There is no single AJR-specific treatment algorithm applicable to every patient. Management is cause-directed and depends on whether the junctional rhythm is compensatory, drug-induced, ischaemia-related, or associated with clinically important haemodynamic compromise.

10. Common interpretation pitfalls

• Calling any rate of 60–100 bpm AJR: the ECG must support a junctional origin; rate alone is insufficient.
• Assuming P waves must be absent: retrograde P waves may be visible before, during, or after QRS complexes.
• Calling AV dissociation complete heart block: AV dissociation can occur when a junctional pacemaker is faster than the sinus node; assess the actual atrial and ventricular rates and conduction pattern.
• Misclassifying wide-complex AJR as ventricular rhythm—or vice versa: compare baseline QRS morphology and look for capture/fusion beats.
• Overlooking digoxin toxicity: a junctional rhythm may be an important clue in the appropriate medication and clinical context.
• Using vagal response as a definitive discriminator: transient slowing does not establish the mechanism; integrate the full ECG and clinical presentation.

12. Interpretation practice

Use the supplied rhythm strip in Figure 1 to practise a structured description. The PDF caption identifies the tracing as AJR with inverted retrograde P waves before the QRS complexes; no patient history or measured rate is supplied for this example.

13. Quick reference summary

14. References