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138 Cards in this Set

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any obstruction or delay of the normal pathways of conduction
conduction block
the sinus node fire normally, but the wave of depolarization is not transmitted into the atrial tissue
sinus node block
(sinus exit block)
any conduction block between the sinus node and the purkinje fibers, including the AV node and His bundle.
AV block
conduction block in one or more of the ventricular bundle branches
bundle branch block
conduction block in only a part of the bundle branches
fascicular block
Name the three types of conduction blocks.
sinus node block
AV block
bundle branch block
Name the three types of AV blocks.
first degree
second degree
third degree
block characterized by a prolonged delay in conduction at the AV node or His bundle
first degree AV block
True or False:
Any routine 12-lead EKG can tell the difference between a block in the AV node and one in the His bundle.
False.
First degree AV blocks are held up at the AV node longer than the usual duration of _______.
one tenth of a second
What interval is prolonged in a first degree AV block?
PR interval
What is required to diagnose first degree AV block?
a PR interval of longer than 0.2 seconds
True or False:
First degree AV block is not really a block, but rather a delay.
True
True or False:
In first degree AV block, there may be some P waves that do not produce a QRS complex.
False.
Every atrial impulse eventually makes it through.
True or False:
First degree AV block is never present in normal hearts.
False.
It is a common finding in normal hearts.
First degree AV block may be normal, or it may be an early sign of what conditions?
degenerated conduction system
myocarditis
drug toxicity
block in which not every atrial impulse is able to pass through the AV node into the ventricles
second-degree AV block
In second-degree AV blocks, the ration of P-waves to QRS complexes is ______.
>1:1
How many types of second-degree AV blocks are there?
2
Name the two types of second-degree AV blocks.
Mobitz I (Wenckebach)
Mobitz II
What is a more common name for a Mobitz I block?
Wenckebach block
A Wenckebach block is almost always due to a block where?
within the AV node
A block in which each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse (usually every third or fourth) fails to make it through
Wenckebach block
True or False:
Wenckebachs are usually characterized by completely irregular sequences of increasing delays followed by dropped beats.
False.
The sequence of delays and dropped beats often repeats itself with impressive regularity.
another way to refer to a Mobitz I that produces a ratio of four P waves to three QRS complexes
4:3 Wenckebach
The diagnosis of this block requires the progressive lengthening of each successive PR interval until one P wave fails to conduct through the AV node and is therefore not followed by a QRS complex.
Mobitz I (Wenckebach)
usually due to a block below the AV node in the His bundle
Mobitz II block
resembles a Wenckebach, except progressive lengthening of the PR interval does not occur
Mobitz II block
Block in which AV conduction is an all or nothing phenomenon
Mobitz II block
True or False:
In a Mobitz II, the ratio of conducted beats to nonconducted beats varies and is rarely constant.
True.
Diagnosis of this block requires the presence of a dropped beat without progressive lengthening of the PR interval.
Mobitz II block
On EKG, it is impossible to make the distinction between an Mobitz I and II at what P-to-QRS ration?
2:1

(impossible to see whether progressive lengthening is occurring)
A cardiologist might be able to localize the site of a 2:1 Mobitz by using this method.
His bundle electrocardiography
(EPS - involves inserting electrodes into the heart)
"ultimate heart block"
third degree AV block
no atrial impulses make it through to the ventricles
third degree AV block
"complete heart block"
third degree AV block
usual site of third degree AV block
at the AV node or lower
How do the ventricles generally respond to a complete heart block?
30-45 bpm
idioventricular escape
(usually inadequate)
block in which the atria and ventricles have virtually nothing to do with each other
third degree AV block
block in which the atria and ventricles are separated by the abcolute barrier of a complete conduction block
third degree AV block
term for any circumstance in which the atria and ventricles are being driven by independent pacemakers
AV dissociation
P waves and QRS complexes appear at regular intervals, but have nothing to do with each other
third degree AV block
(AV dissociation)
True or False:
Suppressing the "PVC-looking" beats of a ventricular escape rhythm could be fatal.
True
Main difference between PVCs and ventricular escape
PVC = premature intrusion beat
Escape = delayed/rescue beat
True or False:
Ventricular escape is always slower than normal beats.
True.
Diagnosis of this block requires the presence of AV dissociation in which the ventricular rate is slower than the sinus or atrial rate.
third-degree AV block
Rhythm that may drive the heart if AV dissociation occurs high in the AV node.
accelerated junctional
True or False:
Pacemakers are virtually always required when a third degree heart block developes.
True.
The ventricular escape is rarely adequate.
True or False:
Pacemakers are rarely required for AV dissociation that occurs high enough in the AV node to produce a junctional escape.
True.
In this case, an accelerated junctional rhythm usually developes at a rate sufficient to adequately drive the heart.
Name the two situations in which high AV dissociation with a junctional escape most often occur.
(1) acute infarction
(2) antiarrhythmic overdose
What is the leading cause of third-degree heart block?
degenerative disease of the conduction system

(may also complicate and AMI)
What EKG observation technique is used to diagnose AV blocks?
examining the relationship between the P waves and the QRS complexes
True or False:
Different degrees of AV block can coexist in the same patient.
True.
True or False:
Blocks are virtually always permanent phenomenon.
False.
Blocks can be transient.
a conduction block in either the left or right bundle branches
bundle branch block
the most efficient means of dispersing the electrical current through the ventricles
bundle branches
normal duration of QRS complex when conduction flows through the bundle branches
less than 0.1 seconds
With this type of block, electrical axis deviates and QRS complex widens.
bundle branch block
block that is diagnosed by looking at the width and configuration of the QRS complexes
bundle branch block
This block is characterized by an obstruction in right bundle branch conduction.
right bundle branch block
block characterized by delayed right ventricular depolarization
right bundle branch block
block in which right ventricular depolarization does not begin until the left ventricle is almost fully depolarized
right bundle branch block
A bundle branch block is generally characterized by a QRS complex that widens to beyond what duration?
0.12 seconds
The QRS complex of a right bundle branch block assumes a unique, virtually diagnostic shape in which leads?
V1, V2
Describe the electrical axis in a right bundle branch block.
sharply toward the right
RSR in leads V1 and V2 indicate what type of block?
right bundle branch block
R-prime in leads V1 and V2 indicate what type of block?
right bundle branch block
What do "rabbit ears" in V1 and V2 indicate?
right bundle branch block
True or False:
In a right bundle branch block, you can still see the initial R and S waves of left ventricular depolarization on V1 and V2.
True.
But as the right ventricle then begins its delayed repolarization, unopposed by the now silent left ventricle, the axis swings to the right and a second R-wave is inscribed.
In right bundle branch block, in which leads are reciprocal, late deep S waves inscribed.
I, AVL, V5, V6
(left lateral leads)
What phenomenon occurs in the left lateral leads in cases of right bundle branch block?
reciprocal changes
How are bundle branch blocks diagnosed on EKG?
by looking at the width and configuration of QRS complexes
criteria for right bundle branch block
(1) QRS complex widened to greater than 0.12 seconds

(2) RSR prime in V1 and V2 (rabbit ears) with ST segment depression and T wave inversion

(3) Reciprocal changes in V5, V6, I and AVL
block characterized by delayed left ventricular depolarization
left bundle branch block
Left bundle branch block is characterized by a characteristic change in the shape of QRS complexes in which leads?
I, AVL, V5, V6
block associated with marked prolongation in the rise of R waves in I, AVL, V5 and V6, which will either be broad on top or notched.
left bundle branch block
block that causes already tall R waves in left lateral leads to become markedly prolonged and broad or notched.
left bundle branch block
True or False:
"Rabbit Ears" in left bundle branch block are less commonly seen than they are in right bundle branch block.
True.
In left bundle branch block, what type of changes are seen in the leads overlying the right ventrical?
reciprocal changes,
broad and deep S waves
True or False:
Left axis deviation is never present in left bundle branch blocks.
False.
Left ventrical is so dominant in left bundle branch blocks that left axis deviation may be present, but this is variable.
True or False:
Repolarization changes are associated with left bundle branch block, but not right.
False.
In both right and left bundle branch block, the repolarization sequence is affected.
What repolarization changes may be associated with bundle branch blocks in overlying leads.
ST depression
T wave inversion
Which leads will show repolarization abnormalities in right bundle branch block?
right precordial leads
Which leads will show repolarization abnormalities in left bundle branch block?
left lateral leads
True or False:
Right bundle branch block is a fairly common phenomenon in otherwise normal hearts.
True.
True or False:
Right bundle branch block can be caused by diseases of the conduction system.
True.
True or False:
Left bundle branch blocks frequently occur in normal hearts.
False.
They almost never occur in normal hearts and almost always reflect significant underlying cardiac disease.
Name two diseases that may manifest in a left bundle branch block.
degenerative disease of the conduction system
ischemic coronary artery disease
True or False:
Bundle branch blocks, once identified, are generally permanent and persistent phenomena that will always appear on EKG.
False:
Both right and left bundle branch blocks can be intermittent or fixed.
In some individuals, a bundle branch block only appears when a particular heart rate, called ________, is achieved.
the critical rate
The development of a rate related bundle branch block is directly related to what factor?
the time it takes for a particular bundle branch to repolarize
the four criteria for left bundle branch block
(1) QRS complex widened to greater than 0.12 seconds

(2) Broad or notched R wave with prolonged upstroke in leads V5, V6, I and AVL, with ST segment depression and T wave inversion

(3) Reciprocal changes in V1 and V2

(4) Left axis deviation may be present.
True or False.
Right bundle branch block precludes the diagnosis of right ventricular hypertrophy and left bundle branch block precludes the diagnosis of left ventricular hypertrophy.
True.
Because bundle branch block affects the size and appearance of R wave, the usual criteria for diagnosing hypertrophy in the same ventricle is useless.
True or False:
Left bundle branch block may lead to a diagnosis of myocardial infarction.
False.
EKG diagnosis of a myocardial infarction cannot be made in the presence of a left bundle branch block.
Term used to refer to a conduction block of just one of the fascicles of the left bundle branch.
hemiblock
True or False:
It is possible for just one fascicle of the right bundle branch to be blocked.
False.
The right bundle branch does not divide into fascicles.
Name the major effect that hemiblocks have on the EKG.
Axis deviation.
block in which conduction down the anterior fascicle of the left ventricle is blocked
left anterior hemiblock
hemiblock in which all the current rushes down the left posterior fascicle to the inferior surface of the heart
left anterior hemiblock
block characterized by left ventricular depolarization that progresses in an inferior-to-superior and right-to-left direction
left anterior hemiblock
block in which the axis of ventricular depolarization is redirected upward and slightly leftward, inscribing tall positive R waves in the left lateral leads and deep S waves inferiorly.
left anterior hemiblock
hemiblock characterized by left axis deviation in which the electrical axis of ventricular depolarization is redirected between -30 and -90 degrees.
left anterior hemiblock
hemiblock characterized by a positive QRS in lead I and a negative QRS in AVF
left anterior hemiblock
In left anterior hemiblock, if the QRS in lead II is negative, then the axis must lie more negative than _____.
negative 30 degrees
a block characterized as "the reverse" of left anterior hemiblock
left posterior hemiblock
block in which all the current rushes down the left anterior fascicle and ventricular myocardial depolarization ensues in a superior-to-inferior and left-to-right direction
left posterior hemiblock
hemiblock in which the axis of depolarization is directed downward and rightward
left posterior hemiblock
hemiblock in which tall R waves are written inferiorly and deep S wave are seen in the left lateral leads
left posterior hemiblock
hemiblock characterized by right axis deviation
left posterior hemiblock
What degree of QRS widening is seen in hemiblock?
Very minor to none.
QRS is basically normal.
What repolarization abnormalities are characteristic of hemiblocks?
None. There are no ST segment and T wave changes.
Between left anterior and posterior hemiblocks, which of the two is more common?
left anterior hemiblock
What is one possible reason that left anterior hemiblock is seen more commonly that left posterior hemiblock?
The anterior fascicle is longer and thinner and has a more tenuous blood supply than the posterior fascicle.
True or false:
Left anterior hemiblocks are seen in both normal and diseased hearts.
True
True or false:
Left posterior hemiblocks is seen in both normal and diseased hearts.
False.
Left posterior hemiblocks are seen almost exclusively in sick hearts.
How is hemiblock diagnosed?
by looking for left or right axis deviation
criteria for left anterior hemiblock
(1) Normal QRS duration and no ST segment or T wave changes

(2) Left axis deviation between -30 and +90 degrees

(3) No other cause of left axis deviation is present
criteria for left posterior hemiblock
(1) Normal QRS duration and no ST segment or T wave changes

(2) Right axis deviation

(3) No other cause of right axis deviation is present
True or False:
A bundle branch block and a hemiblock can occur together.
True.
A right bundle branch block and a hemiblock can occur together.
term that refers to the combination of either a left anterior or left posterior hemiblock with right bundle branch block
bifascicular block
In bifascicular block, what supplies current to the bulk of both ventricles?
Only one fascicle of the left bundle branch
Criteria for bifascicular block (with left anterior hemiblock)
Right bundle branch block
(1) QRS wider than 0.12 seconds
(2) RSR in V1 and V2

Left anterior hemiblock
(3) Left axis deviation between -30 and -90 degrees
Criteria for bifascicular block (with left posterior hemiblock)
Right bundle branch block
(1) QRS wider than 0.12 seconds
(2) RSR in V1 and V2

Left anterior hemiblock
(3) Right axis deviation
early type of pacemaker capable of firing only at a single predetermined rate
fixed rate pacemakers
modern pacemaker that fires only when the patient's own intrinsic heart rate falls below a certain level
demand pacemakers
type of pacemaker in which electrodes are placed into an atrium or ventricle
single-chamber pacemaker
type of packemaker in which electrodes are placed in both the an atrium and a ventricle
dual-chamber pacemaker
(AV sequential pacemaker)
rhythm device that creates a small spike on EKG when it fires
pacemaker
describe the EKG appearance of a ventricular pacemaker
spike followed by a wide and aberrant QRS, just like a PVC
describe the EKG appearance of an atrial pacemaker
spike followed by a P wave and a normal QRS complex
describe the EKG appearance of a sequential pacemaker
two spikes -- one preceding a P wave, and the other proceeding a wide and bizarre QRS
True or False:
A pacemaker spike always has the potential to induce a serious arrhythmia.
True.
However, this is a rare occurence as long as the electrodes maintain good contact with the heart.
True or False:
Patients with left heart failure stand to benefit the most from a pacemaker placed in the right ventricle.
False.
Patients with impaired left ventricular function or CHF may not always benefit from right ventricular pacers.
True or False:
Right ventricular pacers may actually precipitate an episode of heart failure in patient with impaired left ventricular function.
True.
The pacer may override instrinsic conduction pathways in the left ventricle that may be more effective than the pacer, which could weaken left ventricular contraction.
What pacing option is available for patients with impaired left ventricular function?
a third electrode can be threaded into the coronary sinus from the right atrium and passed into the lateral veins of the left ventricle for epicardial pacing.
True or False:
In some patients, a pacemaker spike may be difficult or impossible to see.
True.
Always suspect a pacemaker in the presence of wide QRS complexes and left axis deviation. (Question the patient or check for a pacemaker.)
For most individuals, if the tracing is normal except for the presence of axis deviation, you can feel reasonably confident that ______ is responsible.
hemiblock
If the net QRS deflection in lead II is more negative than positive, then the mean QRS axis must be more negative than ____° (which means ____).
-30

Left Anterior Hemiblock
(LAHB)