AV junctional rhythms

1. The P wave axis is -60 to -80 degrees (normal is 0 to 75 degrees)
2. The P wave of the junctional beat may
   • Precede the QRS in an “upper” nodal rhythm
   • Superimpose on the QRS in a “middle” nodal rhythm
   • Follow the QRS in a “lower” nodal rhythm
   • This depends not only on the location of the pacemaker (upper, middle, or lower) but also on the retrograde conduction of the impulse.
   • There could be a pacemaker located in the upper portion of the node, but if retrograde conduction was slow, then the P wave would not precede the QRS
   • Thus these terms pertaining to the nodal location may be misleading and are no longer used.
3. Typically the PR interval is < .11 second, the RP interval may be up to .20 seconds
4. The morphology of the QRS is not altered.

1. AV junction is the site of impulse formation when there is depression of the SA node, SA block, sinus bradycardia, sinus arrhythmia.
2. In this case the rhythm is an escape rhythm
3. Occurs if the sinus rate is slower than that of the junctional pacemaker (35 to 60 BPM)
4. May occur after the postextrasystolic pause on an atrial or ventricular premature beat.
5. Occasionally the sinus and the AV junctional rhythm ore at similar rates and the P waves and the QRS complexes are in proximity to each other but are unrelated to each other. This phenomenon is called isorhythmic AV dissociation.
6. The ventricular rate increases with atropine
7. The QRS morphology is similar to that in NSR, including any aberrancy
8. May be seen in patients with SA nodal, AV nodal disease, digoxin, healthy people with sinus bradycardia.

1. Junctional tachycardia at a rate > 60 BPM
2. When there is a junctional pacemaker the P waves are inverted in leads 2,3,F.
3. includes premature junctional beats
   • Are premature
   • Morphologic characteristics of an AV junctional beat
   • Usually have a constant coupling interval
   • In most cases the postextrasystolic pause is not fully compensatory. The retrograde conducted impulse discharges the SA node and resets its rhythmicity.
   • Differential diagnosis:

     1. PACs: PJCs more likely if the P waves are inverted inferiorly, if the PR is < .12, and if the QRS is normal in duration.
     2. PVCs: if a retrograde P occurs after the beat, and the RP is < .11, then it is unlikely to be a PVC because the interval is too short to complete VA conduction.
     3. Includes paroxysmal AV junctional tachycardia (AV nodal reentrant and automatic junctional tachycardia)

        • May be due to reentry or increased automaticity.
        • Onset and termination are abrupt. May last seconds, hours or days.
        • Rate 140 to 220 BPM and is regular.
        • The P-QRS complex has the morphologic characteristic of a junctional beat.
        • P waves are inverted in 2,3,F. In many cases they are buried and cannot be identified.
        • QRS can be wide if there is preexistent IVCD.
        • In AV junctional tachycardia, vagal stimulation has little effect on this rhythm
        • Can be seen in healthy patients, those with CAD, and with dig toxicity
        • Includes nonparoxysmal junctional tachycardia (accelerated AV junctional rhythm)

1. Sudden onset of a regular, narrow complex tachycardia
2. Two basic mechanisms: reentry and automaticity
3. Differential diagnosis includes
   • Sinus node reentry

     1. Uncommon, < 5% of cases of SVT
     2. Suggested if the P waves are identical those to the P waves of NSR
     3. Rate is between 100 and 160 BPM (average 130 BPM)
     4. Slower than other forms of PSVT
     5. May be slowed and terminated by CSM

   • Intraatrial reentry

     1. Uncommon with same incidence as sinus node reentry tachycardia
     2. P waves usually upright in inferior leads, have a different morphology than in NSR
     3. Not influenced by CSM

   • AV nodal reentry

     1. Causes 60% of PSVTs
     2. P waves are inverted in the inferior leads
     3. In 2/3rds of these cases they are superimposed on the QRS
     4. In other cases they appear immediately after the QRS
     5. Rate is fast, 140 to 200 BPM
     6. As a rule vagal maneuvers terminate the tachycardia

   • Reentry using an accessory pathway (WPW):

     1. The accessory pathway is either the anterograde or the retrograde pathway of the reentry circuit
     2. If conduction is down the regular AV node, then the QRS is not widened, this is more common.
     3. If conduction is down the accessory pathway, then the QRS is widened.

   • Reentry using a concealed AV bypass tract:

     1. The bypass tract conducts only retrograde, resting EKG is unrevealing
     2. Narrow QRS complex during tachycardia.
     3. In both this and in WPW there are always inverted P waves that follow the QRS.
     4. The fact that P waves can be identified in these tachyarrhythmias is how WPW and bypass tracts can be distinguished for AV nodal reentry tachycardias.
     5. The rate of tachycardias associated with bypass tracts is faster than that due to AV nodal reentry and is 150 to 240 BPM, suspect this when the rate is > 200 BPM.
     6. Although patients with WPW frequently experience tachyarrhythmias, it is more common for a person with a narrow complex tachycardia to have a concealed bypass tract as a cause. Concealed bypass tracts cause 15 to 30% of PSVTs

   • Enhanced automaticity of an atrial focus

     1. P waves always precede the QRS.
     2. May be inverted in the inferior leads if there is a low atrial focus.
     3. Relatively slow, 100 to 180 BPM.
     4. The PR is > .12 seconds.
     5. After a few beats the tachycardia accelerates.
     6. The tachycardia may be associated with AV block (i.e. PAT with block).
     7. Accounts for < 5% of PSVTs.
     8. Vagal maneuvers do not terminate these.

   • Enhanced automaticity of an AV junctional focus

     1. Rare, similar characteristics to that of an atrial focus

1. Abnormal impulse formation at the AV junction.
2. Rate is only moderately increased to about 70 to 130 BPM.
3. Lacks the sudden onset and termination characteristic of the paroxysmal type.
4. Often the result of dig intoxication, acute MI, CT surgery, myocarditis.

1. Occurs when the impulse activates a chamber, returns, and reactivates the chamber again.
2. Used to refer to the phenomenon of one or two beats.
3. If the process continues, it is called reentrant tachycardia.
4. An anterograde and a retrograde pathway are required, and both are usually in the AV node.
5. In Echo beats of atrial origin, there is a P-QRS-P sequence.
6. In Echo beats of ventricular origin, there is a QRS-P-QRS sequence.

1. Hammill S. C. Electrocardiographic diagnoses: Criteria and definitions of abnormalities, Chapter 18, MAYO Clinic, Concise Textbook of Cardiology, 3rd edition, 2007 ISBN 0-8493-9057-5

• ECGpedia: Course for interpretation of ECG
• The whole ECG – A basic ECG primer
• 12-lead ECG library
• Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
• ECG information from Children’s Hospital Heart Center, Seattle
• ECG Challenge from the ACC D2B Initiative
• National Heart, Lung, and Blood Institute, Diseases and Conditions Index
• A history of electrocardiography
• EKG Interpretations in infants and children

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