Accelerated Junctional Rhythm

36. Let’s take Accelerated Junctional Rhythm separately first. This is an irritable arrhythmia that originates in the AV junction and fires at a rate of bpm.

It will have the inverted P wave typical of junctional arrhythmias, or it may have no

P wave if the atria and ventricles depolarize . If the P wave

precedes the QRS complex, the PRI should be less than

second. Conduction through the ventricles is normal, so the QRS complex should have

a measurement of less than 0.12 second.

37. Here are the rules for Accelerated Junctional Rhythm (Figure 43):

Regularity: regular

Rate: 60–100 bpm

P Wave: will be inverted; can fall before or after the QRS complex or can be

hidden within the QRS complex

PRI: can be measured only if the P wave precedes the QRS complex; if

measurable, will be less than 0.12 second

QRS: less than 0.12 second

Tachycardia

60–100

simultaneously

0.12

normal

Figure 41 Mechanism of Accelerated Junctional Rhythm

Retrograde

Pacemaker: AV junction Conduction

speeds up to override

higher sites

Rate: 60–100 bpm

Regularity: regular

Conduction: Atria are

depolarized by retrograde

conduction, while conduction

through the ventricles

proceeds normally

An irritable focus in the AV junction speeds up to override the SA node for control of the heart. The

atria are depolarized via retrograde conduction. Conduction through the ventricles is normal.

Figure 42 Mechanism of Junctional Tachycardia

Retrograde

Pacemaker: AV junction Conduction

speeds up to override

higher sites

Rate: 100–180 bpm

Regularity: regular

Conduction: Atria are

depolarized by retrograde

conduction, while conduction

through the ventricles

proceeds normally

A very rapid irritable focus in the AV junction overrides the SA node for control of the heart. The atria

are depolarized via retrograde conduction. Conduction through the ventricles is normal.

146 Chapter 6

38. When the AV junction fires in the tachycardia range (100–180 bpm) the rhythm

will remain regular. The P waves will be inverted and can fall before or after the

QRS complex, or they might be absent if they are within

the QRS complex. When the P wave precedes the QRS complex, the PRI will

be than 0.12 second. Since conduction through the ventricles

is normal, the QRS complex will be less than second.

39. The rules for Junctional Tachycardia (Figure 44) are:

Regularity: regular

Rate: 100–180 bpm

P Wave: will be inverted; can fall before or after the QRS complex or can be

hidden within the QRS complex

PRI: can be measured only if the P wave precedes the QRS complex; if

measurable, will be less than 0.12 second

QRS: less than 0.12 second

40. The only difference you will see on the EKG among Junctional Escape Rhythm,

Accelerated Junctional Rhythm, and Junctional Tachycardia is the rate. The rates are:

Junctional Escape Rhythm 40–60 bpm

Accelerated Junctional Rhythm 60–100 bpm

Junctional Tachycardia 100–180 bpm

Each of these rhythms originates in the , and will thus produce an inverted P wave because of retrograde conduction. Depending on whether

the atria or ventricles depolarize first, the P wave can come before, during, or after

hidden

less

0.12

AV junction

Figure 43 Rules for Accelerated Junctional Rhyth

ate: 40–60 bpm

P Wave: will be inverted: can fall before or after the QRS complex or can be

hidden within the QRS complex

PRI: can be measured only if the P wave precedes the QRS complex; if

measurable, will be less than 0.12 second

QRS: less than 0.12 second

Junctional Tachycardia

34. Junctional Escape Rhythm is a fail-safe mechanism rather than an irritable arrhythmia. However, the AV junction is capable of irritability and is known to produce an irritable arrhythmia called Junctional Tachycardia. This rhythm occurs when the junction

initiates impulses at a rate than its inherent rate of 40–60 bpm,

thus overriding the SA node or other higher pacemaker sites for control of the heart rate.

Junctional Escape Rhythm is an escape mechanism, whereas Junctional Tachycardia is

an rhythm.

35. Junctional Tachycardia is usually divided into two categories, depending on how

fast the irritable site is firing. If the junction is firing between 60 and 100 bpm, the arrhythmia is termed an Accelerated Junctional Rhythm (Figure 41) because a rate below

100 can’t really be considered a tachycardia. When the junctional rate exceeds 100 bpm,

the rhythm is considered a Junctional Tachycardia (Figure 42). Junctional Tachycardia

can be as fast as 180 bpm, but at this rapid rate, it is extremely difficult to identify positively since P waves are superimposed on preceding T waves. When an AV junctional

focus fires at a rate of 60–100 bpm, it is termed an Junctional

faster

irritable

Accelerated

Figure 40 Rules for Junctional Escape Rhythm

Junctional Escape Rhythm

Regularity: The R–R intervals are constant. The rhythm is regular.

Rate: Atrial and ventricular rates are equal. The inherent rate of the AV junction is 40–60 bpm.

P Waves: The P wave can come before or after the QRS complex, or it can be lost entirely within the QRS complex.

If visible, the P wave will be inverted.

PRI: If the P wave precedes the QRS complex, the PRI will be less than 0.12 second. If the P wave falls within

the QRS complex or follows it, there will be no PRI.

QRS: The QRS complex measurement will be less than 0.12 second.

Junctional Rhythms 145

Rhythm. If the rate exceeds 100 bpm, up to a rate of 180 bpm, the rhythm is called a

Junctional .

Accelerated Junctional Rhythm

36. Let’s take Accelerated Junctional Rhythm separately first. This is an irritable arrhythmia that originates in the AV junction and fires at a rate of bpm.

It will have the inverted P wave typical of junctional arrhythmias, or it may have no

P wave if the atria and ventricles depolarize . If the P wave

precedes the QRS complex, the PRI should be less than

second. Conduction through the ventricles is normal, so the QRS complex should have

a measurement of less than 0.12 second.

37. Here are the rules for Accelerated Junctional Rhythm (Figure 43):

Regularity: regular

Rate: 60–100 bpm

P Wave: will be inverted; can fall before or after the QRS complex or can be

hidden within the QRS complex

PRI: can be measured only if the P wave precedes the QRS complex; if

measurable, will be less than 0.12 second

QRS: less than 0.12 second

Tachycardia

60–100

simultaneously

0.12

normal

Figure 41 Mechanism of Accelerated Junctional Rhythm

Retrograde

Pacemaker: AV junction Conduction

speeds up to override

higher sites

Rate: 60–100 bpm

Regularity: regular

Conduction: Atria are

depolarized by retrograde

conduction, while conduction

through the ventricles

proceeds normally

An irritable focus in the AV junction speeds up to override the SA node for control of the heart. The

atria are depolarized via retrograde conduction. Conduction through the ventricles is normal.

Figure 42 Mechanism of Junctional Tachycardia

Retrograde

Pacemaker: AV junction Conduction

speeds up to override

higher sites

Rate: 100–180 bpm

Regularity: regular

Conduction: Atria are

depolarized by retrograde

conduction, while conduction

through the ventricles

proceeds normally

A very rapid irritable focus in the AV junction overrides the SA node for control of the heart. The atria

are depolarized via retrograde conduction. Conduction through the ventricles is normal.

146 Chapter 6

38. When the AV junction fires in the tachycardia range (100–180 bpm) the rhythm

will remain regular. The P waves will be inverted and can fall before or after the

QRS complex, or they might be absent if they are within

the QRS complex. When the P wave precedes the QRS complex, the PRI will

be than 0.12 second. Since conduction through the ventricles

is normal, the QRS complex will be less than second.

39. The rules for Junctional Tachycardia (Figure 44) are:

Regularity: regular

Rate: 100–180 bpm

P Wave: will be inverted; can fall before or after the QRS complex or can be

hidden within the QRS complex

PRI: can be measured only if the P wave precedes the QRS complex; if

measurable, will be less than 0.12 second

QRS: less than 0.12 second

40. The only difference you will see on the EKG among Junctional Escape Rhythm,

Accelerated Junctional Rhythm, and Junctional Tachycardia is the rate. The rates are:

Junctional Escape Rhythm 40–60 bpm

Accelerated Junctional Rhythm 60–100 bpm

Junctional Tachycardia 100–180 bpm

Each of these rhythms originates in the , and will thus produce an inverted P wave because of retrograde conduction. Depending on whether

the atria or ventricles depolarize first, the P wave can come before, during, or after

hidden

less

0.12

AV junction

Figure 43 Rules for Accelerated Junctional Rhythm

Accelerated Junctional Rhythm

Regularity: The R–R intervals are constant. The rhythm is regular.

Rate: Atrial and ventricular rates are equal. The rate will be faster than the AVjunction’s inherent rate but not yet

into a true tachycardia range. It will be in the 60–100 bpm range.

P Waves: The P wave can come before or after the QRS complex, or it can be lost entirely within the QRS complex.

If visible, the P wave will be inverted.

PRI: If the P wave precedes the QRS complex, the PRI will be less than 0.12 second. If the P wave falls within

the QRS complex or follows it, there will be no PRI.

QRS: The QRS complex will be less than 0.12 second.

Junctional Rhythms 147

the QRS complex. If the P wave precedes the QRS complex, the PRI will be less than

0.12 second. The QRS measurement will be normal. If the rate is 40–60 bpm, the rhythm

is called Rhythm. If the rate is between 60 and 100 bpm, the

rhythm is termed Junctional Rhythm, and the rhythm is called

Junctional Tachycardia if the rate is bpm.

41. A junctional impulse that reaches the atria before the ventricles will produce an

inverted P wave that falls the QRS complex. Such a beat

would have a PRI of less than second. If the PRI were greater

than 0.12 second, you would suspect that the impulse originated in the

.

42. A regular rhythm with a QRS complex of less than 0.12 second and a rate

of 50 bpm, which did not have any visible P waves, would fit the rules for

a Rhythm.

43. A single premature ectopic beat originating from an irritable focus in the AV

junction would be called a PJC, or . Such a beat would have

an inverted P wave that falls , ,

or the QRS complex.

44. All junctional arrhythmias have the same general characteristics; that is,

they all have P waves that can occur before, during, or

after a QRS complex; the PRI will be ; and the QRS will

be . However, not all junctional arrhythmias have the same

mechanism. PJCs, Junctional Tachycardia, and Accelerated Junctional Rhythm are all

caused by irritability, whereas a junctional rhythm within its inherent rate of 40–60 bpm

would be an indication of an mechanism.

Junctional Escape

Accelerated

100–180

before

0.12

atria

Junctional Escape

Premature Junctional Complex

before; during

after

inverted

shortened

normal

escape

Figure 44 Rules for Junctional Tachycardia

Junctional Tachycardia

Regularity: The R–R intervals are constant. The rhythm is regular.

Rate: Atrial and ventricular rates are equal. The rate will be in the tachycardia range but does not usually exceed

180 bpm. Usual range is 100–180 bpm.

P Waves: The P wave can come before or after the QRS complex, or it can be lost entirely within the QRS complex.

If visible, the P wave will be inverted.

PRI: If the P wave precedes the QRS complex, the PRI will be less than 0.12 second. If the P wave falls within

the QRS complex or follows it, there will be no PRI.

QRS: The QRS complex measurement will be less than 0.12 second.

148 Chapter 6

Supraventricular Tachycardia

45. You have now learned several arrhythmias that are regular and beat at such a

rapid rate that the P wave might not be discernible from the T wave. If you include

Junctional Tachycardia, which might not have a visible P wave, you have a group of

tachycardias that are regular and don’t have visible P waves. The ventricular rates for

these arrhythmias are:

Sinus Tachycardia 100–160 bpm

Atrial Tachycardia 150–250 bpm

Atrial Flutter 150–250 bpm

Junctional Tachycardia 100–180 bpm

From these rate ranges you can see that as the rate exceeds 150 or 160 bpm, a rate at which

the P wave could very well be encroaching on the preceding

wave, you would have no way to distinguish between these arrhythmias. Since you

can’t accurately identify the rhythm, you would instead give it a descriptive identification. The term that’s used to describe this category of indistinguishable arrhythmias is

Supraventricular Tachycardias (Figure 45).

46. A Supraventricular Tachycardia (SVT) is not the name of a specific

. It is a term that’s used to a category

of several regular tachyarrhythmias that can’t be identified more accurately because

they have indistinguishable waves and fall within a common

 range.

47. The rates at which you most commonly need to use the term Supraventricular

Tachycardia is the 150–250 range, although sometimes a slower rate will still have

obscured P waves. An SVT is usually a toss-up between Atrial Tachycardia and

Junctional Tachycardia, although Sinus Tachycardia and, less commonly, Atrial

Flutter can also be in the running. These arrhythmias can only be called SVT if

they cannot be identified more accurately. It is not a catch-all phrase. To be

called SVT, an arrhythmia must be , have no visible

 waves, and have a range

common to other arrhythmias, thereby making further and more accurate

identification .

T