*2.4.1 Narrow QRS complex, regular rhythm with short RP interval*

As the name implies, an accelerated junctional rhythm (JR) occurs when the rate of an AV junctional pacemaker exceeds the rate of the sinus node. In this situation,

an increase in automaticity in the AV node occurs in conjunction with a decreasing amount of automaticity in the sinus node (**Figure 9**). There is a possibility that the retrograde impulse from the AV node may suppress the SA node.

Approach to ECG findings: Heart rate > 100 (total R waves on long lead × 6) → Narrow QRS complex (QRS < 120 ms) → Regular RR intervals (RR intervals are equal) → Short RP interval (RP interval < half of RR interval) → Retrograde P waves may be present and appear before, during or after the QRS complex.

There are usually inverted P waves in inferior leads (II, III, aVF), upright P waves in aVR and V1. If the SA node is not suppressed by retrograde AV impulses, AV dissociation may be present with the ventricular rate usually greater than the atrial rate [8].

### **2.5 Permanent junctional reciprocating tachycardia**

#### *2.5.1 Narrow QRS complex, regular rhythm with short RP interval*

This type of tachycardia is also dependent upon the accessory pathway. As the AV node is responsible for generating impulses, these impulses are transmitted retrogradely through the accessory pathways to the atria. This results from characteristically slow conduction of the accessory pathway in permanent junctional reciprocating tachycardia (PJRT) in contrast to AVRT which has a "fast" accessory pathway, **Figure 10**.

Approach to ECG findings: Heart rate > 100 (total R waves on long lead × 6) → Narrow QRS complex (QRS < 120 ms) → Regular RR intervals (RR intervals are equal) → Long RP interval (RP interval > half of RR interval).

Retrograde P waves may be present and appear before, during or after the QRS complex. There are usually inverted P waves in inferior leads (II, III, aVF), upright P waves in aVR and V1. If the SA node is not suppressed by retrograde AV impulses, AV dissociation may be present with the ventricular rate usually greater than the atrial rate.

**Figure 10.** *Slow accessory pathways (red arrow) and the AV node form a reentrant circuit.*

*ECG Approach to Narrow QRS Complex Supraventricular Tachycardia DOI: http://dx.doi.org/10.5772/intechopen.112151*
