AV junctional rhythms

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EKG findings of 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
 * 3) * Precede the QRS in an "upper" nodal rhythm
 * 4) * Superimpose on the QRS in a "middle" nodal rhythm
 * 5) * Follow the QRS in a "lower" nodal rhythm
 * 6) * This depends not only on the location of the pacemaker (upper, middle, or lower) but also on the retrograde conduction of the impulse.
 * 7) * 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
 * 8) * Thus these terms pertaining to the nodal location may be misleading and are no longer used.
 * 9) Typically the PR interval is < .11 second, the RP interval may be up to .20 seconds
 * 10) The morphology of the QRS is not altered.

"Passive" Junctional Rhythms

 * 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.

"Active" Junctional Rhythms

 * 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
 * 4) * Are premature
 * 5) * Morphologic characteristics of an AV junctional beat
 * 6) * Usually have a constant coupling interval
 * 7) * In most cases the postextrasystolic pause is not fully compensatory. The retrograde conducted impulse discharges the SA node and resets its rhythmicity.
 * 8) * Differential diagnosis:
 * PACs: PJCs more likely if the P waves are inverted inferiorly, if the PR is < .12, and if the QRS is normal in duration.
 * 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.
 * 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)

The Frequently Used Term "Paroxysmal Supraventricular Tachycardia"

 * 1) Sudden onset of a regular, narrow complex tachycardia
 * 2) Two basic mechanisms: reentry and automaticity
 * 3) Differential diagnosis includes
 * 4) * Sinus node reentry
 * Uncommon, < 5% of cases of SVT
 * Suggested if the P waves are identical those to the P waves of NSR
 * Rate is between 100 and 160 BPM (average 130 BPM)
 * Slower than other forms of PSVT
 * May be slowed and terminated by CSM
 * 1) * Intraatrial reentry
 * Uncommon with same incidence as sinus node reentry tachycardia
 * P waves usually upright in inferior leads, have a different morphology than in NSR
 * Not influenced by CSM
 * 1) * AV nodal reentry
 * Causes 60% of PSVTs
 * P waves are inverted in the inferior leads
 * In 2/3rds of these cases they are superimposed on the QRS
 * In other cases they appear immediately after the QRS
 * Rate is fast, 140 to 200 BPM
 * As a rule vagal maneuvers terminate the tachycardia
 * 1) * Reentry using an accessory pathway (WPW):
 * The accessory pathway is either the anterograde or the retrograde pathway of the reentry circuit
 * If conduction is down the regular AV node, then the QRS is not widened, this is more common.
 * If conduction is down the accessory pathway, then the QRS is widened.
 * 1) *Reentry using a concealed AV bypass tract:
 * The bypass tract conducts only retrograde, resting EKG is unrevealing
 * Narrow QRS complex during tachycardia.
 * In both this and in WPW there are always inverted P waves that follow the QRS.
 * 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.
 * 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.
 * 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
 * 1) * Enhanced automaticity of an atrial focus
 * P waves always precede the QRS.
 * May be inverted in the inferior leads if there is a low atrial focus.
 * Relatively slow, 100 to 180 BPM.
 * The PR is > .12 seconds.
 * After a few beats the tachycardia accelerates.
 * The tachycardia may be associated with AV block (i.e. PAT with block).
 * Accounts for < 5% of PSVTs.
 * Vagal maneuvers do not terminate these.
 * 1) * Enhanced automaticity of an AV junctional focus
 * Rare, similar characteristics to that of an atrial focus

Nonparoxysmal Junctional Tachycardia (Accelerated AV Junctional Rhythm)

 * 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.

Reciprocal or Echo Beats

 * 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.

Additional resources

 * 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