Junctional Rhythms and Pre-excitation syndromes

Question 1

Re-Entry

Answer 1

As the electrical impulse spins in a loop (Re-entry Loop), it causes waves of depolarization in all directions, which can overdrive the sinus
mechanism and run the heart.

Question 2

Junctional Arrhythmias

Answer 2

● Junctional arrhythmias originate in the Atrioventricular (AV) Junction, which is the
area around the AV node and the Penetrating Fibers.
● When the SA node is suppressed and fails to send impulses, or when the conduction
is blocked, these Junctional Arrhythmias can occur.
○ These occur because Pacemaker cells in the AV Junction begin initiating
electrical impulses
● The impulses move upward and cause a backwards depolarization of the atria (may
cause, but not always, an inverted P-wave in leads II, III, and AVF).
● The impulse also goes down toward the ventricles, causing a forward depolarization
of the ventricles (generally a normal, narrow QRS).

Question 3

The Junctional Arrhythmias Include:

Answer 3

○ Paroxysmal Supraventricular Tachycardia (PSVT)
○ Junctional Escape (discussed in a future unit)
○ Premature Junctional Contractions (discussed in a future unit)

Question 4

Paroxysmal Supraventricular Tachycardia EKG characteristics

Answer 4

○ Regularity = Regular (absolute)
○ Rate = Rapid, usually between 150-250 BPM
○ P Waves = May see retrograde P Waves in Leads II or III, but more often than
not, the P Waves are buried in the QRS. May see Pseudo-R’ or S (next slide)
○ PR Interval = Not usually available
○ QRS Complex = Usually narrow

Question 5

What is this rhythm?

Answer 5

Paroxysmal Supraventricular Tachycardia (PSVT)

Question 6

EKG clue for PSVT

Answer 6

presence of pseudo-R’ waves
(usually in V1, maybe V2) and pseudo-S waves (the inferior leads).

Question 7

There are two main types of PSV

Answer 7

○ AV Nodal Re-entrant Tachycardia (AVNRT) - most common
○ Other cause: Wolff-Parkinson-White Syndrome

Question 8

Vagal maneuvers (such as carotid massage, valsalva, cold water splash) may
trigger increased vagal tone, which may ____

Answer 8

stop the re-entry mechanism

Question 9

____ is preferred for those with recurrent symptomatic AVNRT

Answer 9

Catheter Ablation

Question 10

How to perform Carotid Massage:

Answer 10

○ Auscultate for carotid bruits with the bell. If bruits are present, abort!
○ With the patient lying flat, extend the neck and rotate the head slightly
away from you.
○ Palpate the carotid artery at the angle of the jaw and apply gentle pressure
for 10-15 seconds, right over carotid bifurcation.
○ Never compress both carotid arteries simultaneously.
○ Try the right carotid first (better success rate), but try left if right fails.
○ Have a rhythm strip running during the entire procedure so you can see
what is happening. Always be ready for ACLS protocols

Question 11

what’s the difference between PSVT and Paroxysmal Atrial Tachycardia (PAT) on an EKG?

Answer 11

○ Often times, you can’t tell the difference due to the rapid rate.
■ Both are forms of Supraventricular Tachycardia
○ However, if you see the warm-up and/or cool-down period on the EKG tracing,
it’s likely to be PAT.
○ Additionally, Carotid massage will slow or terminate PSVT, but has virtually no
(or just minimal) effect on PAT.

Question 12

Pre-Excitation Syndromes

Answer 12

● In the Pre-Excitation Syndromes, there are accessory pathways by which the
current can bypass the AV Node and arrive at the ventricles ahead of time
○ Includes Wolff-Parkinson-White and Lown-Ganong-Levine syndromes
● Probably fewer than 1% of people have one of these.
○ Clearly more common in males
● May occur in healthy hearts, or may occur in
conjunction with mitral valve prolapse, hypertrophic cardiomyopathy, and various congenital disorders.

Question 13

Wolff-Parkinson-White Syndrome

Answer 13

● WPW syndrome is an uncommon
condition where there is a bypass pathway
named the Bundle of Kent
● The Bundle of Kent is conducting
tissue that connects the atria to the
ventricle (could be left or right).
○ This allows for a premature ventricular
depolarization

Question 14

WPW EKG changes

Answer 14

● Premature ventricular depolarization causes two things to occur:
Thaler, M. S., MD. (2015). The Only EKG Book You’ll Ever Need (8th ed.). Lippincott Williams & Wilkins.
○ PR Interval is shortened to less than 0.12 sec.
○ The QRS Complex is widened to 3 or just more than 3 mm. This slurs the initial
upstroke of the QRS, leading to what we call the Delta Wave.

Question 15

What is this showing?

Answer 15

Wolff-Parkinson-White Syndrome

Question 16

Patients with WPW and Atrial Fibrillation can develop a dangerous_____, which can be refractory to treatment and can deteriorate into
ventricular fibrillation

Answer 16

A-Fib with RVR

Question 17

Because WPW predisposes to these tachyarrhythmias that can be
dangerous, these patients are at higher risk of _____

Answer 17

sudden cardiac death

Question 18

the procedure of choice for those with high-risk WPW

Answer 18

Catheter Ablation
○ Successful in more than 95% of
WPW patients

Question 19

Lown-Ganong-Levine Syndrome

Answer 19

● LGL Syndrome is a rare accessory
conduction pathway that feeds an
electrical impulse from the atria directly
into the ventricular pathway, bypassing
the AV Node.
○ These accessory fibers are called the
James Fibers
● The electrical impulse bypasses the delay
in the AV Node and depolarizes the
ventricular system early

Question 20

EKG findings for Lown-Ganong-Levine Syndrome

Answer 20

○ PR Interval shortened to
less than 0.12 seconds
○ Narrow QRS Complex
○ No Delta Wave

Question 21

Although it is far less common than with WPW, LGL can also result in
_____

Answer 21

supraventricular tachycardias like PSVT and rapid-response A-Fib.

Question 22

What is this showing?

Answer 22

Lown-Ganong-Levine Syndrome
○ PR Interval shortened to
less than 0.12 seconds
○ Narrow QRS Complex
○ No Delta Wave