• Junctional tachycardia (JT) arises when an ectopic junctional automaticity focus sends out an irritable impulse at a fast rate (often 120-220 bpm) which suppresses normal impulses from the sinus node.
• Because the junctional automaticity focus is located in the lower part of the AV junction (at a far distance from atrial cells), its impulse might not reach the atria and this often times result in absent P wave.
• When impulse from junctional focus reaches the atria in a retrograde fashion, it causes atrial depolarization and retrograde P waves (negatively deflected in inferior leads I, III, aVF and positively deflected in lead V1).
• Since conduction down the His-Purkinje pathway remains intact, QRS complex is normal and narrow.
• JT can sometimes have irregular rhythm (if there is variable AV block) and/or AV dissociation which can differentiate it from AVRT and AVNRT.
• JT is uncommon in adults; whereas a similar rhyhtm, nonparoxysmal junctional tachycardia (NPJT) is more common in adults.
• Nonparoxysmal junctional tachycardia (NPJT) is a more common type of junctional tachycardia in adults.
• NPJT has a slower rate than JT (70-130 bpm) and is often associated with AV dissociation.
• Commonly seen in digoxin toxicity and myocardial infarct.
