Junctional Rhythm Workup

• Evaluation of serum electrolyte levels is generally indicated for patients with comorbidities that may predispose them to accelerated junctional rhythms because of intrinsic bradycardia or AV block.

  • Check digoxin level in patients on digoxin and obtain a 12-lead ECG.
  • The standard approach includes an electrolyte evaluation, a 12-lead ECG, a detailed history, and a physical examination.
  • Check a lyme titer and treat empirically with antibiotics in patients with possible tick exposure in endemic areas.
• Junctional rhythms are common during sleep in younger patients.

Obtain a 2-dimensional echocardiograph in patients with suspected structural heart disease.

Obtain a stress echocardiograph or nuclear imaging test in patients with symptoms consistent with coronary ischemia.

• The 12-lead ECG is essential to making the correct diagnosis of any junctional rhythm (see images below). Telemetry strips demonstrating the onset and termination pattern of the unknown narrow complex rhythm often provide clues regarding the diagnosis. The 12-lead ECG findings also help identify patients with underlying structural heart disease or conduction abnormalities.^[2] Junctional bradycardia due to profound sinus node dysfunction. No atrial activity is apparent. Note the retrograde P waves that precede each QRS complex. Accelerated junctional rhythm is present in this patient. Note the inverted P waves that precede each QRS complex, with a rate of 115 bpm.

  • Determine if the rhythm is regular or irregular, if it is narrow or wide, if P waves are present, if the P waves are from the right atrium (upright in I and II, negative in aVL), how the rhythm was initiated and how it terminated, and, finally, the clinical setting in which the rhythm occurred.
  • A junctional rhythm usually presents with rates from 40-60 beats per minute.
  • Frequently, retrograde P-wave conduction may be notable as a negative P wave in leads I and II and positive in aVL. Because the arrhythmia is originating from within the nodal tissue, near simultaneous activation of the atrium and ventricle occurs. Thus, the P-wave or atrial activation may be hidden within the QRS complex and may not be noticeable on surface ECG findings.
  • Explore the differential diagnosis of a regular narrow complex tachycardia when interpreting the ECG findings. An unusually slow presentation of a tachycardia also may mimic a junctional escape rhythm. These include AV reentry via an accessory pathway, atrial tachycardia, and AV nodal reentrant tachycardia.
  • The differential of a junctional rhythm at lower rates includes a normal response to increased vagal tone during sleep and sinus bradycardia, inappropriate sinus bradycardia, and underlying AV block.
  • ECG findings may help rule out structural or congenital heart disease in patients with evidence of multiple forms of supraventricular arrhythmias.
• A cardiac event monitor is indispensable for patients who are difficult to diagnose, such as those with transient symptoms of palpitations or minimal documentation of an abnormal rhythm. Patients may carry the event monitor for an indefinite period (usually 30 d) and press a button to record a rhythm strip during symptoms. The onset and termination of the rhythm is documented and may help guide therapy and may help exclude more potentially lethal arrhythmias, such as ventricular tachycardia, as a cause of the symptoms.
• An implantable loop recorder may help diagnose junctional rhythm in patients with very infrequent symptoms.
• In patients with an accelerated junctional rhythm after cardiac surgery, documentation of AV conduction is imperative. The accelerated junctional rhythm may be a manifestation of inflammation and/or damage to the AV junction; once the accelerated rhythm resolves, AV block may be present. If atrial epicardial wires are present, pacing the atrium at a more rapid rate allows verification of AV conduction.
• If the diagnosis is still not certain, an electrophysiologic study (EPS) or invasive electrophysiologic evaluation can be performed.^[3]

An EPS should reveal a His bundle depolarization preceding every QRS complex. The His-ventricular interval should be normal unless conduction system disease is present. AV and VA conductions often fluctuate.