Clinical Medicine -- EKG 2 - Junctional Rhythms, Heart Blocks, & Ventricular Rhythms

Premature Junctional Contraction (PJC)

An irritable site in the AV junction fires prematurely, producing a single ectopic beat. Conduction to atria is retrograde while simultaneous conduction to ventricles is normal.

Premature Junctional Contraction (PJC) -- characteristics

-Regularity: depends on rhythm of underlying arrhythmia
-Rate: depends on rate of underlying arrhythmia
-P wave: inverted; can fall before, during, or after QRS complex
-PRI: can only be measured if P wave precedes QRS complex; if measurable, will be less

Junctional Escape Rhythm

When higher pacemaker sites fail, the AV junction takes over. The atria are depolarized via retrograde conduction, while ventricular conduction is normal.

Junctional Escape Rhythm -- characteristics

-Regularity: regular
-Rate: 40-60 beats per minute
-P wave: will be inverted; can fail before, during, or after QRS complex
-PRI: can only be measured if P wave precedes QRS complex; if measurable, will be less than .12 seconds
-QRS: less than .12 seconds

Accelerated Junctional Rhythm

An irritable focus in the AV junction fires repeatedly at a rate faster than the SA node, thus taking over as primary pacemaker. Conduction to atria is retrograde, while simultaneous conduction to ventricles is normal.

Accelerated Junctional Rhythm -- characteristics

-Regularity: regular
-Rate: 60-100 beats per minute
-P wave: will be inverted; can fail before, during, or after QRS complex
-PRI: can only be measured if P wave precedes QRS complex; if measurable, will be less than .12 seconds
-QRS: less than .12 second

Junctional Tachycardia

A single irritable site within the AV junction fires repeatedly at a very rapid rate. Conduction to atria is retrograde, while simultaneous conduction to ventricles is normal.

Junctional Tachycardia

-Regularity: regular
-Rate: 100-180 beats per minute
-P wave: will be inverted; can fail before, during, or after QRS complex
-PRI: can only be measured if P wave precedes QRS complex; if measurable, will be less than .12 seconds
-QRS: less than .12 secon

Supraventricular Tachycardia

Phrase used to describe rapid, regular, supraventricular arrhythmia when accurate identification is impossible (P waves aren't visible & rate is common to other arrhythmias)

SVTs with Overlapping Rate Ranges:

-Sinus Tachycardia (?) -- 100-160 beats/min
-Atrial Tachycardia -- 150-250 beats/min
-Atrial Flutter -- 150-250 beats/min
-Junctional Tachycardia -- 100-180 beats/min

First Degree AV Block

-not a true block
-delay at the AV node
-each impulse is eventually conducted

Second Degree AV Block Types

-Type I: Wenckebach
-Type II: Type II, 2:1 AV block, high-grade AV block

Second Degree AV Block

-intermittent block; some beats are conducted, others are blocked
-pathology can be within the AV node or below it in the Bundle of His
-pathology is often blended with other types of blocks

Third Degree AV Block

-atria and ventricles are completely dissociated
-there is a total block at the AV node

relatively benign

-first degree
-second degree Type I

worrysome

-second degree Type II
-third degree

simplified -- first degree

every P is passed, but delayed

simplified -- second degree

some Ps are passed, some are not

simplified -- third degree

none of the Ps are passed

HALLMARK

first degree and third degree tend to be regular

second degree

-usually has group beating ("holes" in the rhythm)
-Type I, Wenckebach (more good than bad; it gives you a warning that it is going to drop a beat)
-Type II (it gives no warning, QRS simply go away)

first degree heart block

AV node holds each impulse longer than normal before conducting it to the ventricles. Each impulse is eventually conducted

first degree heart block -- characteristics

-Regularity: depends on underlying rhythm
-Rate: depends on underlying rhythm
-P wave: upright and uniform; each P wave followed by QRS complex
-PRI: greater than .20 seconds;
constant across strip
-QRS: less than .12 seconds

Type I second degree heart block (Wenckebach)

Sinus impulses encounter progressive delays in AV node until one impulse is blocked completely and the cycle starts over. Conducted impulses depolarize ventricles normally.

Wenckebach -- characteristics

-Regularity: irregular; R-R interval changes as PR interval gets longer; characteristic grouped beating
-Rate: usually slightly slower than normal
-P wave: upright and uniform; some P waves not followed by QRS complex
-PRI: progressively lengthens until o

Type II second degree heart block

AV node selectively conducts some beats but blocks others. Even beats that are conducted can encounter delays in AV node. Conduction through the ventricles is normal.

Type II second degree heart block -- characteristics

-Regularity: if conduction ratio is consistent, R-R interval will be constant, and rhythm will be regular. if conduction ratio varies, R-R will be irregular
-Rate: atrial rate is usually normal. Since many atrial impulses are blocked, ventricular rate is

classical second degree heart block

-Regularity: can be regular or irregular, depending on whether conduction ratio varies or is constant
-Rate: usually in bradycardia range; can be one half to one third the normal rate
-P wave: upright and uniform; more than one P wave for every QRS comple

complete heart block

the AV node blocks all sinus impulses, so an escape pacemaker from the AV junction or ventricles takes over to pace the ventricles. Atria and ventricles are totally dissociated

complete heart block -- characteristics

-Regularity: regular
-Rate: 40-60 beats per minute if focus is junctional; 20-40 beats per minute if focus is ventricular
-P wave: upright and uniform; more P waves than QRS complexes
-PRI: no relationship between P waves and QRS complexes; P waves occasi

Premature Ventricular Contractions (PVC)

An irritable focus within the ventricles fires prematurely to initiate a single ectopic complex

Premature Ventricular Contractions (PVC) -- characteristics

-Regularity: ectopics will disrupt regularity of underlying rhythm
-Rate: depends on underlying rhythm and number of ectopics
-P wave: not preceded by a P wave; dissociated P waves may be seen near PVC
-PRI: since the ectopic comes from a lower focus, the

Ventricular tachycardia

a single irritable focus within the ventricles fires very rapidly, thus overriding higher sites for control of the heart

ventricular tachycardia -- characteristics

-Regularity: usually regular; can be slightly irregular
-Rate: usually 150-250 beats/min; less than 150 is called slow VT
-P wave: not preceded by P waves; dissociated P waves may be seen
-PRI: none
-QRS: wide and bizarre; .12 seconds or greater

Ventricular Fibrillation

multiple foci in the ventricles become irritable and generate uncoordinated, chaotic impulses that cause the heart to fibrillate rather than contract

ventricular fibrillation -- characteristics

regularity, rate, P wave, PRI, QRS --> totally chaotic with no discernible waves or complexes

idioventricular rhythm

absence of a higher pacemaker allows the much slower ventricles to assume control of the heart

idioventricular rhythm -- characteristics

-Regularity: usually regular (it can be unreliable since it is such a low site)
-Rate: 20-40 beats per minute; can drop below 20 beats per minute
-P wave: none
-PRI: none
-QRS: wide and bizarre; .12 seconds or greater

asystole

there is no electrical pacemaker to initiate electrical flow. the heart has lost its electrical activity

asystole -- characteristics

regularity, rate, P wave, PRI, QRS --> straight line indicates absence of electrical activity