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138 Cards in this Set
- Front
- Back
any obstruction or delay of the normal pathways of conduction
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conduction block
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the sinus node fire normally, but the wave of depolarization is not transmitted into the atrial tissue
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sinus node block
(sinus exit block) |
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any conduction block between the sinus node and the purkinje fibers, including the AV node and His bundle.
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AV block
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conduction block in one or more of the ventricular bundle branches
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bundle branch block
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conduction block in only a part of the bundle branches
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fascicular block
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Name the three types of conduction blocks.
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sinus node block
AV block bundle branch block |
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Name the three types of AV blocks.
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first degree
second degree third degree |
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block characterized by a prolonged delay in conduction at the AV node or His bundle
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first degree AV block
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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.
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First degree AV blocks are held up at the AV node longer than the usual duration of _______.
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one tenth of a second
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What interval is prolonged in a first degree AV block?
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PR interval
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What is required to diagnose first degree AV block?
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a PR interval of longer than 0.2 seconds
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True or False:
First degree AV block is not really a block, but rather a delay. |
True
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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. |
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True or False:
First degree AV block is never present in normal hearts. |
False.
It is a common finding in normal hearts. |
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First degree AV block may be normal, or it may be an early sign of what conditions?
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degenerated conduction system
myocarditis drug toxicity |
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block in which not every atrial impulse is able to pass through the AV node into the ventricles
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second-degree AV block
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In second-degree AV blocks, the ration of P-waves to QRS complexes is ______.
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>1:1
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How many types of second-degree AV blocks are there?
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2
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Name the two types of second-degree AV blocks.
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Mobitz I (Wenckebach)
Mobitz II |
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What is a more common name for a Mobitz I block?
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Wenckebach block
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A Wenckebach block is almost always due to a block where?
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within the AV node
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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
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Wenckebach block
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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. |
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another way to refer to a Mobitz I that produces a ratio of four P waves to three QRS complexes
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4:3 Wenckebach
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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.
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Mobitz I (Wenckebach)
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usually due to a block below the AV node in the His bundle
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Mobitz II block
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resembles a Wenckebach, except progressive lengthening of the PR interval does not occur
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Mobitz II block
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Block in which AV conduction is an all or nothing phenomenon
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Mobitz II block
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True or False:
In a Mobitz II, the ratio of conducted beats to nonconducted beats varies and is rarely constant. |
True.
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Diagnosis of this block requires the presence of a dropped beat without progressive lengthening of the PR interval.
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Mobitz II block
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On EKG, it is impossible to make the distinction between an Mobitz I and II at what P-to-QRS ration?
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2:1
(impossible to see whether progressive lengthening is occurring) |
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A cardiologist might be able to localize the site of a 2:1 Mobitz by using this method.
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His bundle electrocardiography
(EPS - involves inserting electrodes into the heart) |
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"ultimate heart block"
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third degree AV block
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no atrial impulses make it through to the ventricles
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third degree AV block
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"complete heart block"
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third degree AV block
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usual site of third degree AV block
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at the AV node or lower
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How do the ventricles generally respond to a complete heart block?
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30-45 bpm
idioventricular escape (usually inadequate) |
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block in which the atria and ventricles have virtually nothing to do with each other
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third degree AV block
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block in which the atria and ventricles are separated by the abcolute barrier of a complete conduction block
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third degree AV block
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term for any circumstance in which the atria and ventricles are being driven by independent pacemakers
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AV dissociation
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P waves and QRS complexes appear at regular intervals, but have nothing to do with each other
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third degree AV block
(AV dissociation) |
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True or False:
Suppressing the "PVC-looking" beats of a ventricular escape rhythm could be fatal. |
True
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Main difference between PVCs and ventricular escape
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PVC = premature intrusion beat
Escape = delayed/rescue beat |
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True or False:
Ventricular escape is always slower than normal beats. |
True.
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Diagnosis of this block requires the presence of AV dissociation in which the ventricular rate is slower than the sinus or atrial rate.
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third-degree AV block
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Rhythm that may drive the heart if AV dissociation occurs high in the AV node.
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accelerated junctional
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True or False:
Pacemakers are virtually always required when a third degree heart block developes. |
True.
The ventricular escape is rarely adequate. |
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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. |
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Name the two situations in which high AV dissociation with a junctional escape most often occur.
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(1) acute infarction
(2) antiarrhythmic overdose |
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What is the leading cause of third-degree heart block?
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degenerative disease of the conduction system
(may also complicate and AMI) |
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What EKG observation technique is used to diagnose AV blocks?
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examining the relationship between the P waves and the QRS complexes
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True or False:
Different degrees of AV block can coexist in the same patient. |
True.
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True or False:
Blocks are virtually always permanent phenomenon. |
False.
Blocks can be transient. |
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a conduction block in either the left or right bundle branches
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bundle branch block
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the most efficient means of dispersing the electrical current through the ventricles
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bundle branches
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normal duration of QRS complex when conduction flows through the bundle branches
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less than 0.1 seconds
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With this type of block, electrical axis deviates and QRS complex widens.
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bundle branch block
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block that is diagnosed by looking at the width and configuration of the QRS complexes
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bundle branch block
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This block is characterized by an obstruction in right bundle branch conduction.
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right bundle branch block
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block characterized by delayed right ventricular depolarization
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right bundle branch block
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block in which right ventricular depolarization does not begin until the left ventricle is almost fully depolarized
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right bundle branch block
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A bundle branch block is generally characterized by a QRS complex that widens to beyond what duration?
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0.12 seconds
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The QRS complex of a right bundle branch block assumes a unique, virtually diagnostic shape in which leads?
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V1, V2
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Describe the electrical axis in a right bundle branch block.
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sharply toward the right
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RSR in leads V1 and V2 indicate what type of block?
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right bundle branch block
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R-prime in leads V1 and V2 indicate what type of block?
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right bundle branch block
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What do "rabbit ears" in V1 and V2 indicate?
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right bundle branch block
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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. |
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In right bundle branch block, in which leads are reciprocal, late deep S waves inscribed.
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I, AVL, V5, V6
(left lateral leads) |
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What phenomenon occurs in the left lateral leads in cases of right bundle branch block?
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reciprocal changes
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How are bundle branch blocks diagnosed on EKG?
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by looking at the width and configuration of QRS complexes
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criteria for right bundle branch block
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(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 |
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block characterized by delayed left ventricular depolarization
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left bundle branch block
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Left bundle branch block is characterized by a characteristic change in the shape of QRS complexes in which leads?
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I, AVL, V5, V6
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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.
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left bundle branch block
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block that causes already tall R waves in left lateral leads to become markedly prolonged and broad or notched.
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left bundle branch block
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True or False:
"Rabbit Ears" in left bundle branch block are less commonly seen than they are in right bundle branch block. |
True.
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In left bundle branch block, what type of changes are seen in the leads overlying the right ventrical?
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reciprocal changes,
broad and deep S waves |
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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. |
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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. |
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What repolarization changes may be associated with bundle branch blocks in overlying leads.
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ST depression
T wave inversion |
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Which leads will show repolarization abnormalities in right bundle branch block?
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right precordial leads
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Which leads will show repolarization abnormalities in left bundle branch block?
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left lateral leads
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True or False:
Right bundle branch block is a fairly common phenomenon in otherwise normal hearts. |
True.
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True or False:
Right bundle branch block can be caused by diseases of the conduction system. |
True.
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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. |
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Name two diseases that may manifest in a left bundle branch block.
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degenerative disease of the conduction system
ischemic coronary artery disease |
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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. |
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In some individuals, a bundle branch block only appears when a particular heart rate, called ________, is achieved.
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the critical rate
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The development of a rate related bundle branch block is directly related to what factor?
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the time it takes for a particular bundle branch to repolarize
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the four criteria for left bundle branch block
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(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. |
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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. |
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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. |
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Term used to refer to a conduction block of just one of the fascicles of the left bundle branch.
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hemiblock
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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. |
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Name the major effect that hemiblocks have on the EKG.
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Axis deviation.
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block in which conduction down the anterior fascicle of the left ventricle is blocked
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left anterior hemiblock
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hemiblock in which all the current rushes down the left posterior fascicle to the inferior surface of the heart
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left anterior hemiblock
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block characterized by left ventricular depolarization that progresses in an inferior-to-superior and right-to-left direction
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left anterior hemiblock
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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.
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left anterior hemiblock
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hemiblock characterized by left axis deviation in which the electrical axis of ventricular depolarization is redirected between -30 and -90 degrees.
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left anterior hemiblock
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hemiblock characterized by a positive QRS in lead I and a negative QRS in AVF
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left anterior hemiblock
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In left anterior hemiblock, if the QRS in lead II is negative, then the axis must lie more negative than _____.
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negative 30 degrees
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a block characterized as "the reverse" of left anterior hemiblock
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left posterior hemiblock
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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
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left posterior hemiblock
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hemiblock in which the axis of depolarization is directed downward and rightward
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left posterior hemiblock
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hemiblock in which tall R waves are written inferiorly and deep S wave are seen in the left lateral leads
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left posterior hemiblock
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hemiblock characterized by right axis deviation
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left posterior hemiblock
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What degree of QRS widening is seen in hemiblock?
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Very minor to none.
QRS is basically normal. |
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What repolarization abnormalities are characteristic of hemiblocks?
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None. There are no ST segment and T wave changes.
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Between left anterior and posterior hemiblocks, which of the two is more common?
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left anterior hemiblock
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What is one possible reason that left anterior hemiblock is seen more commonly that left posterior hemiblock?
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The anterior fascicle is longer and thinner and has a more tenuous blood supply than the posterior fascicle.
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True or false:
Left anterior hemiblocks are seen in both normal and diseased hearts. |
True
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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. |
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How is hemiblock diagnosed?
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by looking for left or right axis deviation
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criteria for left anterior hemiblock
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(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 |
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criteria for left posterior hemiblock
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(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 |
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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. |
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term that refers to the combination of either a left anterior or left posterior hemiblock with right bundle branch block
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bifascicular block
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In bifascicular block, what supplies current to the bulk of both ventricles?
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Only one fascicle of the left bundle branch
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Criteria for bifascicular block (with left anterior hemiblock)
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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 |
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Criteria for bifascicular block (with left posterior hemiblock)
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Right bundle branch block
(1) QRS wider than 0.12 seconds (2) RSR in V1 and V2 Left anterior hemiblock (3) Right axis deviation |
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early type of pacemaker capable of firing only at a single predetermined rate
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fixed rate pacemakers
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modern pacemaker that fires only when the patient's own intrinsic heart rate falls below a certain level
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demand pacemakers
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type of pacemaker in which electrodes are placed into an atrium or ventricle
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single-chamber pacemaker
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type of packemaker in which electrodes are placed in both the an atrium and a ventricle
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dual-chamber pacemaker
(AV sequential pacemaker) |
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rhythm device that creates a small spike on EKG when it fires
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pacemaker
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describe the EKG appearance of a ventricular pacemaker
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spike followed by a wide and aberrant QRS, just like a PVC
|
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describe the EKG appearance of an atrial pacemaker
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spike followed by a P wave and a normal QRS complex
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describe the EKG appearance of a sequential pacemaker
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two spikes -- one preceding a P wave, and the other proceeding a wide and bizarre QRS
|
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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. |
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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.
|
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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.) |
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For most individuals, if the tracing is normal except for the presence of axis deviation, you can feel reasonably confident that ______ is responsible.
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hemiblock
|
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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) |