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EKG
Tutorial: Junctional Rhythms
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Premature Junctional Contractions
The AV node, just like the other cardiac
tissue, has automaticity.
, the AV node is stimulated before it fires by itself. Occasionally, however,
an extra impulse may develop in the junction, thereby spreading up to the atria,
and down to the ventricles. Just like the PACs
described earlier, these Premature Junctional Contractions occur periodically.
A PJC may be seen in a patient with respiratory difficulty. The poor gas exchange irritates myocardial tissue and causes abnormal activity. PJCs are generally not treated because they are harmless.
PJCs are distinguished from PACs by the P-wave. A PAC has a fairly normal looking P-wave... upright and round. PJCs, however, do not originate in the atria, therefore, the atrial depolarization moves up toward the base of the heart, rather than downward toward the apex. P-waves from PJCs will be inverted (look at the 3rd and 5th complexes in the picture). Often, the P-wave will occur along with the montrous QRS complex, and will therefore be hidden from view.
Junctional Escape Complexes
If no stimulus reaches the AV node, the cells assume that the SA node never fired. The AV junction will reach it's automatic threshold and generate an action potential. Unlike PJCs, the escape complexes will appear late in the rhythm (which is why they occurred, and why they are called escape beats!). Otherwise, they posess the same deformed, inverted, or absent P-waves of any other junctional beat. The QRS complex will remain narrow, because the impulses are originating above the ventricles.
Clinically, PJCs are not usually treated. They are one of the many quirks that we all experience at one time or another. Escape complexes, on the other hand, are not such a good thing. The complexes themselves are good (because without them, you're heart would simply not beat). Rather, the clinician must investigate why they are occuring:
As always, we use the ECG as a diagnostic tool, but we examine and treat the patient!!
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FreeMedStud (c) 2002 by Aaron Segal
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