Chapter 6: Rhythm, Part II: Blocks Flashcards
Blocks ______ or _______ the conduction of ______________ stimuli.
retard, prevent, depolarization
p. 173
Blocks can develop in…
…the SA Node, AV Node, the His Bundle, the Bundle Branches, or in either of the two subdivisions of the Left Bundle Branch (called a Hemiblock).
(p. 173)
With Sinus Block, an unhealthy SA Node stops its pacing activity for at least ___ ________ _____, so the block is usually _________.
However, remember that the pause may induce an ______ ____ from an automaticity focus.
one complete cycle
transient
escape beat
(p. 174)
Some experts claim that the SA Node does generate a stimulus, but that it is blocked from _______ the __ ____. This is referred to as Sinus “____” Block.
leaving, SA Node
“Exit”
(p. 174)
Sick Sinus Syndrome is a wastebasket of arrhythmias caused by SA Node dysfunction associated with ____________ supraventricular automaticity foci, which are also _____________ and can’t employ their normal escape mechanism to assume ______ ______________.
unresponsive
dysfunctional
pacing responsibility
(p. 175)
____ _____ ________ most often occurs in elderly patients who have heart disease.
Sick Sinus Syndrome (SSS)
p. 175
SSS is usually characterized by marked _____ ___________, but without the normal escape mechanisms of atrial and junctional foci. It may also present as recurrent episodes of _____ _____ or _____ ______ associated with faulty or ______ escape mechanisms of all supraventricular foci.
sinus bradycardia
Sinus Block or Sinus Arrest
absent
(p. 175)
Because of extensive parasympathetic innervation to the SA Node and all supraventricular foci, excessive parasympathetic activity depresses the pacing rate of the SA Node, as well as the atrial and junctional foci. Therefore, young, healthy conditioned athletes, who often have _______________ _____________ at rest, appear to exhibit convincing signs of SSS (a.k.a. “______” SSS).
parasympathetic hyperactivity
pseudo-
(p. 175)
Patients with SSS may develop intermittent episodes of ___ (sometimes even atrial _______ or atrial ____________) mingled with the sinus bradycardia. This is called ___________-___________ ________.
SVT, flutter, fibrillation
Bradycardia-Tachycardia Syndrome
(p. 175)
The AV Blocks either ______ and/or _________ conduction from the atria to the ventricles.
retard, eliminate
p. 176
Minor AV blocks simply ________ the brief pause btw atrial and ventricular ______________.
But, MOST AV blocks __________ block some or all supraventricular impulses from reaching the __________.
lengthen, depolarization
completely, ventricles
(p. 176)
A first degree block retards __ ____ conduction, prolonging the __ ________ more than one large square (___ ___) on EKG.
AV Node, PR interval, 0.2 sec
p. 177
The PR interval is measured from the _________ of the _ ____ to the beginning of the ___ _______.
Keep in mind that technically, a “segment” is a _______ of ________, while as “interval” contains __ _____ ___ ____.
beginning, P wave, QRS complex
portion of baseline, at least one wave
p. 177
A 1st degree block is present when the PR interval is ____________ prolonged the ____ amount in every cycle, and the P-QRS-T sequence is normal in every cycle also.
consistently, same
p. 178
2nd degree AV blocks allow ____ atrial depolarizations to conduct to the ventricles, while some are _______, leaving lone P waves without an associated ___.
some, blocked
QRS
(p. 179)
2nd degree blocks of the __ ____ are “Wenckebach”, formerly called “___ ______ ____ _”.
2nd degree blocks of ________ _____ bundles (His bundle or bundle branches) are ______, formerly called “___ ______ ____ _”.
AV Node, 2nd degree type I
Purkinje fiber, Mobitz, 2nd degree type II
(p. 179)
In a Wenckebach 2nd degree AV block, the PR interval gradually _________ in successive cycles, but the last P wave of the series fails to _______ to the __________.
Lengthens
Conduct to the ventricles
(p. 180)
The typical Wenckebach pattern (“footprint”) consists of anywhere from ___ to _____ or more cycles.
Two to eight
p. 180
Wenckebach is sometimes caused by _______________ excess or drugs that mimic such effects.
Parasympathetic
p. 180
Repeating short series of Wenckebach footprints can produce _____ _______ that looks somewhat like couplets of premature beats. Don’t be ______!
“group beating”
fooled!
(p. 180)
Mobitz (a.k.a. type II) 2nd block totally blocks a number of paced atrial depolarizations (P waves) before __________ to the __________ is successful. This produces ___ (2 P waves to one QRS) or ___ (three P waves to one QRS) or even higher AV ratios.
conduction, ventricles
2: 1 or 3:1
p. 181
Mobitz is a serious problem because it results in _________ ____ ventricular rates, which may produce _______.
extremely slow, syncope
p. 181
Poorer conduction ratios (i.e. 4:1, 5:1, etc.) relate to increased ________ of the block and are sometimes called “________” Mobitz block.
severity, advanced
p. 181
Warning! With Mobitz, every cycle that is missing its QRS has a regular, ________ _ ____ – but never a _________ __ wave. This distinction is critical!
punctual P wave
premature P’
(p. 181)
Both Wenckebach and Mobitz have dropped ___’s, so how can you differentiate?
It is most likely Wenckebach if the __ ________ is __________, but the QRS is ______.
It is most likely Mobitz if the __ ________ is ______, but the QRS is _______.
QRS
PR interval, lengthened, normal
PR interval, normal, widened
(p. 182)
Because Wenckebach commonly originates in the __ ____ a ___ AV block of this origin often has an initial __________ __ with no wide ___ pattern.
AV Node, 2:1, lengthened PR, QRS
p. 182
But since Mobitz originates below the AV Node, usually in the ___ ______, we recognize that it often has a normal __ with a _______ ___.
His Bundle, PR, widened QRS
p. 182
Occasionally an EKG of 2:1 block has criteria that fit both Wenchebach and Mobitz. To differentiate, the judicious use of a _____ ________ may be required.
vagal maneuver
p. 183
The AV Node is richly supplied with _______________ ___________, so vagal maneuvers will inhibit the AV Node. If the block is Wenckebach, the maneuvers will ________ the number of cycles/series to produce 3:2 or 4:3 Wenckebach.
But…. if the 2:1 block is Mobitz, vagal maneuvers either eliminate the block, producing ___ __ conduction, or they have __ ______.
parasympathetic innervation
increase
1:1 AV, no effect
(p. 183)
With every EKG check, begin by looking at the PR interval. It is increased ____________ in a ___ degree AV block,
it _____________ increases in each series of cycles with Wenckebach,
it is _______ ________ in 3rd degree AV block, and
_________ in WPW and ___ syndromes.
consistently, 1st
progressively
totally variable
decreased LGL
(p. 184)
Next, check to see if every P has a QRS. If not, consider…
…2nd degree or 3rd degree block.
p. 184
In a complete AV block (or 3rd degree block), a total block of __________ to the __________, so atrial depolarizations do not reach the ventricles. Therefore, an automaticity focus _____ the complete block escapes to pace the ventricles at its ________ ____.
conduction, ventricles
below, inherent rate
(p. 186)
In a 3rd degree block, if a junctional focus emerges to pace the ventricles, we should expect to see ______ (______) QRS’s pacing at a rate of __ to __/min.
narrow (normal), 40 - 60
p. 188
In a 3rd degree block, if a ventricular focus emerges to pace the ventricles, we should expect to see ____ (___-____) QRS’s pacing at a rate of __ to __/min. This is so slow that _______ may ensue. This is also called ______-_____ ________.
wide (PVC-like), 20 - 40, syncope
Stokes-Adams Syndrome
(p. 189)
We understand that a ventricular focus could only escape to pace if there were no __________ ____ available above it. So the complete block either obliterated the entire AV Node or it occurred below the __ ________.
junctional foci, AV junction
p. 189
Don’t be trapped by ________ that ____ complex bradycardia is always due to 3rd degree block.
assuming, wide
p. 190
Extremely high serum K+ concentrations can ________ _______ the SA Node and supraventricular foci, producing the same EKG findings as downward displacement of the pacemaker.
severely depress
p. 190
Downward displacement of the pacemaker carries a poor prognosis, however, the prognosis is worse for ____ _________, diminished _________, and slower ___________ ____.
wider complexes, amplitude, ventricular rate.
p. 190
A block of one of the Bundle branches produces a _____ of depolarization of the ventricle it supplies.
Therefore, in BBB, one ventricle depolarizes slightly later than the other, causing 2 “______ ___’s” to appear.
delay, “joined QRS’s”
p. 191, 192
With an EKG tracing, those larger deflections cause the needle to lag behind a bit mechanically, sometimes giving us an exaggerated duration on the tracing. Therefore it is best to check the ____ _____ for QRS duration (where QRS amplitude is minimal).
limb leads
p. 193
Caution: If a patient with BBB develops SVT, the rapid succession of extra wide QRS’s may imitate ___________ ___________.
ventricular tachycardia
p. 193
If there is a BBB, look at leads _____, and _____ for the R,R’.
V1-V2 and V5-V6
p. 195
If there is an R,R’ in _____, (the right chest leads) then there is probably a right BBB.
V1 - V2
p. 196
With a BBB, an R,R’ in the left chest leads, _____, means that LBBB is present.
V5 - V6
p. 197
If you see an R,R’ in a QRS of normal duration, this is referred to as a…
…incomplete BBB.
p. 198
Simultaneous RBBB and LBBB prevents depolarization from reaching the ventricles, which is a ________ __ _____. So, block of one bundle branch with intermittent block of the other produces…
Complete AV block
…intermittent complete AV block, intermittent Mobitz
(p. 199)
Right BBB plus intermittent LBBB will record as continuous _____ ___ pattern QRS’s with intermittent episodes of ________ __ _____. (And vice versa)
right BBB,
complete AV block
(p. 199)
Three important scenarios can imitate intermittent Mobitz:
A Wenckebach series produces a barren span of baseline after the terminal, ________ _ ____, which is not conducted.
A non-conducted Premature Atrial Beat strikes the __ ____ which it is still refractory, so no stimulus is conducted to the __________; notice the peculiar, premature __ before the barren baseline.
A transient sinus block (remember _______ is missing), can produce a pause before pacing resumes, or an automaticity focus may respond with an ______ ____; in either case there is never an ________ _ ____ preceding the pause.
punctual P wave
AV Node, ventricles, P’
P-QRS-T
escape beat
isolated P wave
(p. 200)
Simply stated:
punctual P wave (no QRS response)…
premature P’ wave (no QRS response)…
missed P-QRS-T cycle…
…2nd degree AV block; Mobitz vs. Wenckebach
…non-conducted PAB
…SA Node transiently blocked (Sinus Block)
(p. 200)
