Junctional RhythmsJunctional Rhythms

Electrical impulses that originate from the AV node (junction).

AV Node (The Gatekeeper)

Three main functions:• Slows conduction to allow time

for the atria to contract & empty

its contents (atrial kick) before

the ventricles contract• Secondary pacemaker (40 – 59 bpm)• Blocks some of the impulses

from being conducted to the

ventricles when atrial rate is rapid

AV Node P Waves

See Overhead Slide 4-1

Premature Junctional ContractionPremature Junctional Contraction

A premature junctional contraction (PJC) is an earl beat that originates in the AV junction.

As a result of increased automaticity within junctional cells

Premature Junctional ContractionPremature Junctional Contraction

Rhythm: Premature ectopic beat causes slight irregularity

Rate: Overall HR depends on rate of underlying rhythm

P waves: P wave may be inverted, come after the QRS complex, or be lost in the QRS complex.

PRI: 0.12 – 0.20 sec on regular beat; ectopic beat is visible PRI will be < 0.12 sec; if P wave is late or not visible there will be

no PRI.

QRS: Narrow (< 0.12 sec); sometimes wide

Junctional Escape BeatJunctional Escape Beat

An ectopic junctional beat that occurs late within an underlying rhythm

P wave will be inverted (before the QRS), hidden (within the QRS), or late &

inverted (after the QRS)

Junctional Escape BeatJunctional Escape Beat

Common after a pause in the underlying rhythm:

Sinus arrest

Sinus (exit) block

Nonconducted PAC

Mobitz I

Junctional RhythmJunctional RhythmAppears secondary to depression of the SA node

Occurs when the SA node is firing at a rate lower than that of the inherent rate of the AV node

Or if the electrical impulse of the SA node fails to reach the AV node

If the AV node does receive an impulse within 1 – 1.5 seconds, it is triggered to fire resulting in a

junctional escape beat or rhythm

Junctional RhythmJunctional Rhythm

Causes:

Disease of the SA node

Acute MI

Drug Effects (digitalis, quinidine, BB’s, or CCB’s)

May also occur with Complete Heart Block

Junctional RhythmJunctional Rhythm

Rhythm: Regular

Rate: 40 – 60 bpm (impulse originates from AV junction)

P waves: Consistently either inverted before QRS, hidden in QRS complex, or inverted & after the QRS complex

PRI: usually < 0.12 sec but may be 0.12 – 0.20 sec; if P wave is late or not visible there will be no PRI

QRS: Narrow (< 0.12 sec); sometimes wide

Junctional RhythmJunctional Rhythm

Accelerated Junctional RhythmAccelerated Junctional Rhythm

Causes:

Enhanced automaticity secondary to digitalis toxicity

Damage to the AV node secondary to acute inferior wall MI, heart failure, acute rheumatic fever, myocarditis, valvular heart disease, and

cardiac surgery (especially valve surgery)

Accelerated Junctional RhythmAccelerated Junctional Rhythm

Junctional TachycardiaJunctional Tachycardia

Causes:

Enhanced automaticity secondary to digitalis toxicity

Damage to the AV node secondary to acute inferior wall MI, heart failure, acute rheumatic fever, myocarditis, valvular heart disease, and

cardiac surgery (especially valve surgery)

Junctional TachycardiaJunctional Tachycardia

Often confused with SVT if the rate is very fast causing the P wave to become

hidden

If a P wave cannot be differentiated, then it is acceptable to use the term Paroxysmal

SVT or PSVT to describe the rhythm

Junctional TachycardiaJunctional Tachycardia

Rhythm: Regular (usually)

Rate: 101 – 180 bpm (impulse originates from AV junction)

P waves: Consistently either inverted before QRS, hidden in QRS complex, or inverted & after the QRS complex

PRI: usually < 0.12 sec but may be 0.12 – 0.20 sec; if P wave is late or not visible there will be no PRI

QRS: Narrow (< 0.12 sec); sometimes wide

TIME TO WORKOUT!!!TIME TO WORKOUT!!!

ReferencesReferencesChernecky, C., et al. (2002). Real world nursing survival guide:

ECG’s & the heart. United States of America: W. B. Saunders Company.

Huff, J. (2006). ECG workout: Exercises in arrhythmia interpretation (5th ed.). United States of America: Lippincott, Williams & Wilkins.

Walraven, G. (1999). Basic arrhythmias (5th ed.). United States of America: Prentice-Hall, Inc.

www.madsci.com/manu/ekg_rhy.htm