Introduction

Accelerated junctional rhythm and junctional tachycardia are basically the same rhythm, with rate being the only modifier separating them. The rates for accelerated junctional rhythm are between .60 and 100 beats per minute (BPM); those for junctional tachycardia are typically greater than 100 to 200 BPM (Figure 24-1). At rates at or above 140 BPM, the edges blur between what is considered a junctional tachycardia and what is considered an atrioventricular nodal reentry tachycardia (AVNRT; see Chapter 25, AV Nodal Reentry Tachycardia), and either term is technically correct when referring to a rhythm strip or ECG. We do want to make the point, however, that in the electrophysiology lab the rates can go as high as 200 BPM for simple junctional tachycardia. Clinically, at the patient’s bedside, rates greater than 140 BPM should be labeled and initially treated as if the rhythm is an AVNRT.

Figure 24-1 The spectrum of the junctional rhythms caused by increased intrinsic automaticity within the AV node and junctional area.

© Jones & Bartlett Learning.

Description

Accelerated junctional and junctional tachycardia are both caused by increased automaticity of the atrioventricular (AV) junction. They have the usual junctional morphology of narrow, supraventricular complexes and inverted P waves in leads II, III, and aVF that can be buried slightly before, or slightly after, the QRS complex. Junctional tachycardias are usually regular, although rarely, slight alterations in the cadence can develop. In these rare cases, the rhythm may resemble atrial fibrillation.

Junctional tachycardias with wide QRS complexes are difficult to distinguish from ventricular tachycardias. Wide complexes can be seen in patients with pre-existing bundle branch blocks, aberrancy, or electrolyte abnormalities.

If retrograde conduction is present, the conduction ratios between the P wave and the QRS complexes remain constant. This is because the sinus node is consistently reset at a rate inherently faster than the normal sinus rate, essentially shutting off the sinoatrial node. If the retrograde conduction of the impulse is blocked, the sinus node and the atria will beat at their own pace, essentially causing two rhythms: an atrial rhythm and a ventricular rhythm, which is controlled by the junctional rate. (This is a condition known as AV dissociation. We will see this again in Chapter 28, Atrioventricular Blocks.)