b. Premature Junctional Contraction.
(1) Analysis. Premature junctional contraction (PJC) is another form of
heart abnormality. This condition occurs when a small region of the heart becomes
more excitable than normal. This causes an occasional abnormal impulse to be
generated between the normal impulses. The abnormal impulse is generated from the
region of the heart called the ectopic focus. A wave of depolarization spreads out from
the ectopic focus and causes a premature contraction. The regularity depends on the
regularity of the underlying rhythm, and the rate depends on the rate of the underlying
rhythm. P waves will be inverted and can fall before, during, or after the QRS complex.
The PR interval can only be measured if the P wave precedes the QRS Complex. The
QRS complex lasts less than 0.12 of a second. What happens is that the AV node
takes over the pacemaking function.
(2) Treatment. Treatment is the same as for premature atrial contractions
(PACs). See paragraph 2-8c.
The normal inherent rate of atrial ventricular junction is 40 to 60 beats per
minute. If higher pacemaker sites fail, a junctional escape pacemaker might
take control of the heart. The rhythm would then be called a junctional escape
rhythm. Inherent rates are as follows: atria--75 beats/minute; A-V node - 60
beats/minute; ventricles--40 to 60 beats per minute; and normal heart rate -
60 to 100 beats per minute.
Figure 2-21. Premature junctional contractions (PJC).