Discussion
The rhythm is regular at a rate of 72 beats/min, although the fourth and ninth QRS complexes (*) are associated with a slightly shorter interval (rate 80 beats/min) (Figure 2).
Figure 2.
Accelerated junctional rhythm. Image courtesy of Dr Podrid.
The QRS complexes have a normal duration (0.08 sec) and a normal morphology and axis between 0° and +90° (positive QRS complex in leads I and aVF). The QT/QTc intervals are normal (360/395 msec). P waves are seen (+), occurring at a regular interval (↔) and a rate of 56 beats/min. There is no association between the P waves and the QRS complex—the PR intervals are variable; hence, atrioventricular (AV) dissociation is present.
There are two etiologies for AV dissociation. The first is complete AV block in which the atrial rate is faster than the rate of the QRS complexes, which represent an escape and therefore occur at a slower rate; the escape rhythm may be junctional or ventricular based on the morphology of the QRS complex and not the rate of the escape rhythm. The second is an accelerated lower pacemaker (junctional or ventricular based on the morphology of the QRS complexes). Because the QRS complexes are normal, these are junctional QRS complexes. In this situation, the atrial rate is slower than the rate of the QRS complexes; therefore, this is an accelerated junctional rhythm. The fourth and ninth QRS complexes (*) are slightly early, meaning that they are in response to the P wave that precedes them. Furthermore, the PR interval associated with these two complexes is the same (0.32 sec). These two complexes are therefore conducted.
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Cite this: Philip J. Podrid. ECG Challenge: Revelations of a 'Routine' ECG - Medscape - Apr 20, 2016.
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