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Idiojunctional rhythm

Instructors' Collection ECG: Junctional or Low Atrial Rhythm

Sun, 06/10/2018 - 13:33 -- Dawn

The Patient   This ECG was recorded from an 86-year-old man who was weak, pale, and diaphoretic. He was hypotensive, with a BP of 88/54.  He denied chest pain or shortness of breath.

The ECG   The 12-lead ECG shows a bradycardia at about 60 beats per minute and regular.  The QRS complexes are narrow, at a little less than .08 seconds (800 ms).  The P waves are negative in Leads II, III, and aVF and positive in aVR.  This is an indication that the P waves are traveling in a “retrograde” fashion – backward. The origin of the P waves has to be the AV junction or the lower atria for this to happen.  The PR interval is on the short side of normal at about .12 seconds (120 ms), possibly even less.  This is common in junctional rhythm, as the impulse starts at the AV junction, and travels back through the atria and forward through the ventricles at the same time.

There are no premature beats, and the ST segments are not elevated or depressed. There are no T wave inversions, except for aVR, where it is normal.

Assessment    One cause of junctional rhythm is sinus brady.  That is, the sinus node begins firing so slowly that the junctional pacemaker “escapes”, and takes control of the heart.  When the sinus node speeds up, it may once again take over the heart’s rhythm from the junction.  The fastest pacemaker controls the heart. A junctional rhythm may escape when the sinus node fails or there is a complete AV block in the AV node area.

Patient Outcome    This patient was diagnosed with orthostatic hypotension, bronchitis, and urinary tract infection. He was treated in the hospital and cleared by a cardiologist for discharge two days later.

Our thanks to Michael Francis and Chris Burden for donating this ECG.

ECG Basics: Junctional Rhythm

Sat, 12/28/2013 - 18:59 -- Dawn

A basic rhythm strip showing junctional rhythm in Lead II.  The junctional pacemaker is located between the atria and the ventricles, and the resulting P wave is caused by retrograde conduction through the atria.  This causes the P wave to be negatively deflected in Lead II.  In junctional rhythms, the P wave can occur just before the QRS, during the QRS, or after the QRS, or may not be seen at all.  If the P wave occurs before the QRS, the PR interval is usually short, reflecting the fact that the atria and the ventricles are depolarized almost simultaneously.  In this example, the PRI is .12, on the short side of normal.

The junctional pacemakers have a slow intrinsic rate so that the sinus node can remain in control of the heart's rate under normal circumstances.  If the sinus rate drops below the intrinsic rate of the junctional pacemaker, the junction will take over control of the heart.  An idiojunctional rhythm is generally between 40 and 60 bpm.  In this example, it is about 63 bpm.

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