Dubin Ch 5 Rhythm Flashcards
What causes the SA node pacing rate to varie almost imperceptibly?
Respiration
Pg 100
True or false. All automaticity foci pace with a regular rhythm?
True
Pg 99
The atrial conduction system consists of three specialized internodal tracks in the right atrium, name them.
Name the conduction tract that innervates the left atrium.
Anterior, middle, posterior
Bachman’s bundle
Pg 101
From where do the three conduction pathways in the right atrium originate and terminate?
Originate from the SA node and terminate at the AV node
Pg 101
What wave is produced by atrial depolarization?
P wave
Pg 101
What is the coronary sinus?
The hearts own venous drainage system that empties into the right atrium
Pg 101
What produces a pause on an EKG between a P-wave and the QRS complex?
The slowing of conduction in the AV node
Pg 102
Does the proximal or distal end of the AV node have automaticity foci?
The distal end, aka, AV junction
Pg 102
QRS complex represents what?
Ventricular depolarization
Pg 103
Why does left to right depolarization of the septum occur?
The left bundle branch produces fine terminal filaments, the right bundle branch does not, so left to right depolarization occurs before the rest of the ventricular myocardium depolarizes.
Pg 104
Ventricular depolarization persists through the end of the __________.
T-wave
Pg 104
Ventricular contraction begins and ends during…
The QT interval
Pg 104
What is it U wave?
It represents the final phase of Purkinje repolarization and occurs following the T-wave
Pg 104
If an automaticity foci suddenly becomes irritable will it pace fast or slow?
Very fast
Pg 105
Name the general categories that arrhythmias can be divided into.
Irregular rhythms escape premature beats tachy-arrhythmias These are categorized according to the mechanism of origin Pg 106
What are irregular rhythms usually caused by and how can they be classified?
Usually caused by multiple active automaticity sites
A wandering pacemaker
Multifocal atrial tachycardia
Atrial fibrillation
Pg 107
Describe what is meant by the term parasystolic when referring to an automaticity foci.
In a heart with structural pathology or hypoxia, foci may suffer from an “entrance” block. Any incoming depolarization is blocked, thereby they cannot be overdrive suppressed while their own automaticity is still conducting to surrounding tissues.
Pg 107
Describe a wandering pacemaker rhythm.
An irregular rhythm produced by the pacemaker activity wandering from the SA node to nearby atrial automaticity foci. Cycle length variation Variation in the shape of P waves. Rate <100. Pg 108
Describe multifocal atrial tachycardia (MAT).
Irregular rhythm P-wave shape varies Atrial rate >100 Irregular ventricular rhythm Atrial foci show early signs of parasystole (entrance block) by developing a resistance to overdrive suppression. No single foci achieves pacemaking dominance. They all pace together. Pg 109
What health conditions is MAT associated with?
COPD and sometimes digitalis toxicity
Pg 109
Describe atrial fibrillation.
Irregular rhythm Continuous chaotic atrial spikes Irregular ventricular rhythm Continuous rapid multiple atrial foci. No single impulse depolarizes the atria completely. Only random atrial depolarization's reach the AV node. This produces irregular QRS complexes. Pg 110
How do you determine the general ventricular rate in a fib?
By counting the number of QRS complexes in a six second strip and multiply by 10.
Pg 110
What is an escape rhythm and what are the three types of escape rhythm?
An automaticity focus escapes overdrive suppression to pace at it's inherent rate. Atrial escape rhythm Junctional escape rhythm Ventricle escape rhythm Pg 112
What is an escape beat and what are the three types of escape beats?
Automaticity focus transiently escapes overdrive suppression to emit one beat. Atrial Escape Beat Junctional Escape Beat Ventricle Escape Beat Pg 112
Describe escape
The response of an automaticity focus to a pause in the pacemaking activity
Pg 112
What rhythm occurs when SA node pacing ceases entirely and an automaticity focus paces at it inherent rate?
Sinus Arrest and an Escape rhythm
Pg 112-113
Why are automaticity foci overdrive suppressed?
Because they are depolarized by a pacing rate faster than it’s own inherent pacing rate.
Pg 113
Describe sinus block.
The SA node misses one pacing cycle and produces a transient pause. An automaticity focus produces an escape beat in an attempt to become the dominant pacer but the return of SA node pacing, overdrive suppresses it again.
Pg 113
Describe an atrial escape rhythm
Originates in an atrial automaticity focus
P waves are not identical to previous P waves produced by the SA node.
Inherent rhythm is 60-80 BPM.
Pg 114
Describe a Junctional Escape Rhythm (idojunctional rhythm)
If there is sinus arrest accompanied by atrial foci failure, automaticity focus in the AV junction escapes overdrive suppression and becomes the dominant pacemaker with a rate of 40-60 BPM.
Can also occur due to a complete block in the proximal AV node.
Pg 115
What is the exception to a junctional escape rhythm producing a series of lone QRS complexes?
Retrograde Atrial Depolarization. Characterized by an inverted P-wave in leads with an upright QRS.
Pg 116
Describe retrograde atrial depolarization.
Occurs when junctional automaticity focus conducts to the ventricles as expected, but also depolarize the atria from below. This produces an inverted P-wave in EKG leads with an upright QRS.
Pg 116
What are the 3 patterns retrograde atrial depolarization may record on an EKG?
Inverted P-wave immediately prior to each QRS
Inverted P-wave after each QRS
Inverted P-wave buried with in each QRS
Pg 116
Describe ventricular escape rhythm.
If a ventricular automaticity focus is not depolarized from above it escapes overdrive suppression and becomes the dominant pacemaker with an inherent rate of 20-40 BPM
Pg 117
Ventricular escape rhythms result from one of two mechanisms. What are they?
- A complete conduction block below the AV node and ventricular foci are not stimulated by atrial depolarizations
- SA node, Atrial foci, and AV junction foci all fail and produce a condition called “downward displacement of the pacemaker”. The ventricle foci become the pacemaker in an attempt to sustain life.
Pg 117
What is Stokes-Adams?
Unconsciousness caused by poor brain perfusion due to pacing from the ventricular foci
What happens in transient sinus block with the SA node?
The SA node misses a pacing stimulus that produces a pause and an atrial focus emits an escape beat. (A.K.A.atrial escape beat)
p118-119
What does the EKG look like for an atrial escape beat?
A pause of one cardiac cycle is followed by a P-wave that differs from the other P waves
p119
What is a junctional escape beat?
When a transient sinus block is present junctional automaticity foci can emit an escape beat. It may produce retrograde atrial depolarization, with an inverted P-wave immediately before or after the QRS.
p120
What is a ventricular escape beat?
Occurs when the atrial and junctional foci fail to suppress a ventricular escape beat. This happens in excessive parasympathetic innervation. On an EKG it will produce an enormous QRS complex.
p121
What is a premature beat?
It is caused by an irritable foci that fire spontaneously and earlier than expected. Ventricular foci are very sensitive to oxygen. If low oxygen is sensed, they react.
Atria and junctional foci become irritable due to what types of conditions?
Usually adrenergic stimulants such as Epi, caffeine or any beta-1 receptors stimulants. Also any increased sympathetic stimulation, some toxins and hypothyroidism, low O2.
p123
What is a premature atrial beat?
A premature beat that produces an earlier P-wave than expected due to an irritable atrial foci. The P-wave is unusually shaped and maybe hiding on the peak of the T-wave, the T-wave will look taller than the others.
p124
Can a premature atrial beat reset the rhythm based on the premature beat?
Yes, if a retrograde depolarization occurs to the dominant automaticity center, usually the SA node. If not, it will not reset the rhythm.
p125
What does the EKG look like of a premature atrial beat with aberrant ventricular conduction?
Early P-wave that does not look like all the others, followed by a wide QRS complex. This is due to one of the bundle branches not completely repolerizing and remaining slightly refractory.
p126
What is a non-conducted premature atrial beat?
When a premature atrial depolarization reaches the AV node prior to its repolarization, it is not conducted to the ventricles resulting in no QRS on an EKG.
p128
What is a premature Junctional beat?
A premature fire of the AV junction that stimulates the ventricle and sometimes the atria.
p131
What should you expect to see on an EKG with a PJB?
A premature QRS complex that is slightly widened
p 131
What does a PJB look like on an EKG if it depolarizes the atria in a retrograde fashion?
In inverted P wave with an upright QRS
Describe Junctional Bigeminy and Junctional Trigeminy
Bigeminy- A PJB occurs after each normal SA node cycle
Trigeminy- a PJB occurs after 2 consecutive cycles
Describe atrial bigeminy and atrial trigeminy.
A premature atrial beat that couples to the end of a normal cycle and repeats itself is atrial bigeminy. If it couples itself after two normal cycles, it is trigeminy.
EKG look for a premature P-wave in each couplet.
p. 133
What causes ventricular irritability?
Low O2, Low K+, Specific Pathology
p.135
Describe what a PVC is and what it looks like on an EKG.
Represents a premature, irritable ventricular foci that creates a wider, taller and deeper QRS complex that usually has the opposite deflection of the main QRS’s. (one area of the ventricular wall depolarizes before the rest of the wall.
p.135
What is a compensatory pause after a PVC?
The PVC does not reset the SA node, so it continues to fire on schedule, so the next P-wave does fire but the ventricles are refractory and so there is a pause until the following P-wave and QRS.
p. 137
How many PVC/min is considered pathological, and what do identical PVC indicate?
6, they are emanating from the same irritable ventricular focus (hypoxia)
p.138
Describe Ventricular Bigeminy, Trigeminy and Quadgeminy
Bi- PVC’s coupled with every normal cycle
Tri - PVC’s coupled with every 2 normal cycles
Quad - PVC’s couple with every 3 normal cycles
p. 139
Describe Ventricular Parasystole
When a ventricular foci escapes :overdrive suppression” and is able to fire at its own inherent rate. (dual rhythm)
p. 140
How can PVCs resemble V-tach?
A run of 3 or more consecutive PVCs is basically the same thing as V-tach, only not lasting. (very irritable ventricular foci). If lasting > 30s = V-tach
p. 141
Describe Multifocal PVCs
Multiple ventricular focus are firing, each producing its own unique, identifiable PVC. Indicates severe cardiac hypoxia
p. 142
What is Mitral Valve Prolapse and how can it cause PVCs?
During ventricular systole the mitral valve prolapses into the atria and pulls on the chordae where it attaches to the ventricle. This causes stretch and ischemia leading to irritable ventricular foci.
p.143
Why is a “R on T” dangerous?
When a PVC fires on a T wave or too soon after, the ventricle is still trying to repolarize and this can lead to dangerous arrythmias.
p. 144
What are the three main types of tacy-arrythmias and their rate ranges?
Paroxysmal Tachycardia 150-250, Flutter 250-350, Fibrilation 350-450
p. 145
What are the 3 types of Paroxysmal (sudden) tachycardia?
Atrial, Junctional, Ventricular
p.148
Describe PAT
Rapid firing of atrial foci that overdrive suppress the SA node at a rate of 150-250. P waves don’t look normal but do conduct to create a normal QRS.
p.149
What is PAT with block look like and what can cause it?
rate 150-250
2 P-waves per QRS
Caused by digitalis excess or toxicity
p. 150
Describe PJT and what it looks like
Irritable Foci in the AV Junction, may produce retrograde atrial depolarization resulting in an inverted P-wave before, after or within each QRS. May produce a wide QRS due to unequal refractory of R/L Bundle Branches
p.151
Common name for PAT and PJT
PSVT (SVT)
Is there independent pacing of the atria and ventricles in PVT? Describe PVT
yes
SA node still paces the atria but P wave is typically not visible due to large QRS (a.k.a AV dissociation)
PVT is actually runs of PVC’s with a rate of 150-250
p. 154
Possible indications of PVT
Coronary insufficiency and poor oxygenation, can lead to irritable ventricular foci
p.156
What could cause SVT to look like VT?
SVT with aberrant conduction produces wide QRS. Also a Bundle Branch Block w/ SVT will widen QRS complex.
NEVER give Adenosine to a pt. with VT
p. 156
Distinguish between SVT and VT
SVT = QRS.14 sec, AV dissociation is common, Extreme right axis deviation is common, CVD is common
p. 157
What does Torsades de Point look like?
Brief episodes of 250-350 ventricular rhythm that look like a twisted ribbon.
p.158
Describe atrial flutter
rapid back-to-back atrial depolarization waves at a rate of 250-350, where only 1 out of every 2 or 3 conduct through the AV node to the ventricles due to its long refractory period. Looks like “saw teeth”.
p. 159
What can you do to assist in identifying atrial flutter?
Invert the strip or employ a vagal maneuver to see if the “saw teeth” waves are then revealed
p.160
How does a vagal maneuver help identify atrial flutter?
By increasing AV node refractoriness and allowing fewer atrial fluters to be conducted to the ventricles.
p.160
What does ventricular flutter look like?
Rapid rate 250-350 with smooth “sine” waves of similar amplitude that rarely resolves itself.
p. 161
What does ventricular flutter almost always progress into?
V-Fib
If a paroxysmal tachycardia has identifiable P waves and normal QRS it could not have originated in an irritable ___________, and therefor must be ____________
ventricle focus
some type of supra ventricular tachycardia
p. 163
Define fibrillation
erratic rhythm caused by continuous rapid discharges from foci in either the atria or ventricle. These foci suffer from entrance block and are parasystolic. The can not be overdrive suppressed
p. 164
Describe atrial fibrillation
Many irritable parasystolic atrial foci rapidly fire and only occasional depolarizations are conducted through the AV node to the ventricles resulting in an irregular ventricular rate
p. 165
Identify A-fib on an EKG
Irregularly irregular, with no discernible P waves. Treat the ventricular rate appropriately if it is out of a safe range.
p. 166
Describe ventricular fibrulation
Many irritable parasystolic ventricular foci rapidly fire and only depolarize small sections of the ventricle resulting in twitching of the ventricles
p. 167
Identify VF on an EKG
Totally erratic appearance and lack of identifiable waves on an EKG
p. 168
Describe Wolf-Parkinsons-White
When the bundle of Kent “bypasses” the delay of the AV node and prematurely excites the ventricles. Causes the illusion of a shortened PRI and lengthened QRS.
p. 171
Describe Lown-Ganong-Levine Syndrome
The AV node is bypassed by the James Bundle, an extension of the anterior internal tract, and conducts atrial depolarizations past the AV node delay directly to the Bundle of His. Can result in very fast ventricular rates in patients with rapid atrial rates.
p. 172
