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Junctional rhythm

Atrial Fib To Cardiac Arrest

Sun, 07/03/2016 - 14:31 -- Dawn

A paramedic crew responded to the office of a local physician. A 61-year-old male presented with a one-week history of chest pain and shortness of breath. He had a previously undiagnosed atrial fibrillation with rapid ventricular response and left bundle branch block, but was alert. Shortly after transport commenced, the patient became unresponsive with Torsades de Pointes, which rapidly degenerated into ventricular fibrillation. The paramedic placed pads and defibrillated within one minute.  After two minutes of compressions, the patient had a fairly regular rhythm with return of spontaneous circulation.  Transport time was short.  On catheterization, the patient was found to have severe coronary artery disease, requiring coronary artery bypass graft surgery (CABG) A balloon pump was inserted in an attempt to strengthen him for surgery.

What is the rhythm?   The 12-lead ECG presented here shows atrial fibrillation at a rate of 138 per minute.  The rhythm is irregularly-irregular with no P waves.  Since the patient had not yet been diagnosed with atrial fib, obviously no therapy had been initiated to control the rate. There is a PVC near the end of the strip.

ECG Basics: Retrograde P Waves

Wed, 03/02/2016 - 23:04 -- Dawn

This Lead II rhythm strip is from a nine-year-old girl being monitored for an outpatient surgical procedure.  She has no known heart disease.  Her heart rate is 110 per minute.  The PR interval is .12 seconds (120 ms), the QRS is upright and narrow at .06 seconds (60 ms), and the rhythm is regular.

The most noticeable abnormality here is the RETROGRADE P WAVES.  In Lead II, normal P waves are upright.  In this case, the rhythm is being initiated in the lower atria, or possibly in the AV junction.  The impulse is traveling backward, or in a retrograde fashion, toward the SA node.  The electrical impulse travels forward, or in an antegrade direction, to produce a NORMAL QRS complex.  Retrograde P waves that are very close to the QRS, or within it, are presumed to occur from a junctional rhythm, as the impulse leaves the ectopic pacemaker and travels forward and backward at the same time.  When a normal PR interval is present, it is probably more likely that the impulse originated in the lower atrial tissue, and is delayed as it travels through the AV node.

This ECG abnormality is probably of no clinical significance in a healthy child, but should be worked up in a child with cardiac symptoms or complaints.  This strip is a very good one for illustrating retrograde and antegrade conduction to beginning students.

ECG Basics: Retrograde P Waves

Tue, 10/20/2015 - 22:28 -- Dawn

This Lead II rhythm strip shows a regular rhythm with narrow QRS complexes and retrograde P waves.  The strip was taken from a nine-year-old girl.  The rate is about 110 per minute and the PR interval is .12 seconds (120 ms).

When retrograde conduction is seen in the atria, it is often assumed that the rhythm is originating in the junction.  When a junctional pacemaker is initiating the rhythm, the atria and ventricles are depolarized almost simultaneously.  This can produce a P wave in front of the QRS with a short PR interval, during the QRS, or after the QRS.  Sometimes, in junctional rhythm, a block prevents the impulse from entering the atria, producing NO P wave.  Junctional rhythms are usually slow "escape" rhythms, but can be accelerated or tachycardic.

The fact that this rate is 110 / minute and the PR interval is normal at .12 seconds, we should consider that this rhythm could also be from an ectopic pacemaker low in the atria.  From this low starting point, the impulse will travel backward, in a "retrograde" fashion, through the atria, producing a negatively-deflected P wave in Lead II.

We do not have clinical data on this patient, and so do not know what possible causes of arrhythmia might be present, and what the expected rate should be in this situation.  

Complete AV Block With Junctional Escape Rhythm

Thu, 09/03/2015 - 23:02 -- Dawn

This ECG was taken from a 90-year-old woman.  We have no other history, unfortunately.  It is a good example of a sinus rhythm with complete AV block, also called third-degree AV block.

The defining characteristics of this rhythm include:   1) an underlying rhythm that is regular and with a physiological rate.  In other words, the P waves are not so fast that they would not be expected to conduct one-to-one.  2)  a second rhythm of regular QRS complexes that is unrelated to the P waves.

Occasionally, a P wave may occur before a QRS and appear to have a PR interval.  This is just a chance meeting, as both rhythms (P waves and QRS complexes) are regular AT DIFFERENT RATES, so we would expect them to occur near each other from time to time.  NONE of the P waves are being conducted to the ventricles to produce QRS complexes. This is a good ECG to demonstrate "marching out" the P waves to see that they are very regular, even though some are hidden in the QRS, ST segment, or T waves.

In this case, the "escape rhythm" occurs from the AV junction.  The AV junctional pacemakers are "set" at a rate of about 40 - 60 beats per minute.  Normally, the sinus rhythm arrives in the AV junction faster than that, depolarizing the junctional pacemakers and preventing them from firing spontaneously.  In complete AV block, the atrial impulse never arrives, so the junctional pacemaker is free to "escape" and become the primary pacemaker of the heart.  We recognize this rhythm as junctional because the QRS complexes are narrow, and the rate is around 40 bpm.  Knowing that the escape rhythm is from the junction tells us that the AV block is in the AV node.  The AV junction is the first available pacemaker below the block.  Had the complete AV block been lower, in the bundle branches, the QRS would have come from the ventricles and would have been wide and slower.

In very general terms, this "supra-Hisian" type of AV block is preferable to a "sub-Hisian" block.  The rate is faster, and the QRS complexes narrow, both conditions causing a better cardiac output than wide QRS complexes and extremely slow rates.  However, the effect of the block on the patient has a lot to do with the cause of the block and the symptoms the slow rate cause.  Emergency treatment of the rate may be necessary if it causes a drop in blood pressure and perfusion.  Some patients with this type of block will need a permanent implanted pacemaker, but not all. 

 

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