Ekg - Conduction Blocks

Front 1

any obstruction or delay of the normal pathways of conduction

Back 1

conduction block

Front 2

the sinus node fire normally, but the wave of depolarization is not transmitted into the atrial tissue

Back 2

sinus node block
(sinus exit block)

Front 3

any conduction block between the sinus node and the purkinje fibers, including the AV node and His bundle.

Back 3

AV block

Front 4

conduction block in one or more of the ventricular bundle branches

Back 4

bundle branch block

Front 5

conduction block in only a part of the bundle branches

Back 5

fascicular block

Front 6

Name the three types of conduction blocks.

Back 6

sinus node block
AV block
bundle branch block

Front 7

Name the three types of AV blocks.

Back 7

first degree
second degree
third degree

Front 8

block characterized by a prolonged delay in conduction at the AV node or His bundle

Back 8

first degree AV block

Front 9

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.

Back 9

False.

Front 10

First degree AV blocks are held up at the AV node longer than the usual duration of _______.

Back 10

one tenth of a second

Front 11

What interval is prolonged in a first degree AV block?

Back 11

PR interval

Front 12

What is required to diagnose first degree AV block?

Back 12

a PR interval of longer than 0.2 seconds

Front 13

True or False:
First degree AV block is not really a block, but rather a delay.

Back 13

True

Front 14

True or False:
In first degree AV block, there may be some P waves that do not produce a QRS complex.

Back 14

False.
Every atrial impulse eventually makes it through.

Front 15

True or False:
First degree AV block is never present in normal hearts.

Back 15

False.
It is a common finding in normal hearts.

Front 16

First degree AV block may be normal, or it may be an early sign of what conditions?

Back 16

degenerated conduction system
myocarditis
drug toxicity

Front 17

block in which not every atrial impulse is able to pass through the AV node into the ventricles

Back 17

second-degree AV block

Front 18

In second-degree AV blocks, the ration of P-waves to QRS complexes is ______.

Back 18

>1:1

Front 19

How many types of second-degree AV blocks are there?

Back 19

2

Front 20

Name the two types of second-degree AV blocks.

Back 20

Mobitz I (Wenckebach)
Mobitz II

Front 21

What is a more common name for a Mobitz I block?

Back 21

Wenckebach block

Front 22

A Wenckebach block is almost always due to a block where?

Back 22

within the AV node

Front 23

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

Back 23

Wenckebach block

Front 24

True or False:
Wenckebachs are usually characterized by completely irregular sequences of increasing delays followed by dropped beats.

Back 24

False.
The sequence of delays and dropped beats often repeats itself with impressive regularity.

Front 25

another way to refer to a Mobitz I that produces a ratio of four P waves to three QRS complexes

Back 25

4:3 Wenckebach

Front 26

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.

Back 26

Mobitz I (Wenckebach)

Front 27

usually due to a block below the AV node in the His bundle

Back 27

Mobitz II block

Front 28

resembles a Wenckebach, except progressive lengthening of the PR interval does not occur

Back 28

Mobitz II block

Front 29

Block in which AV conduction is an all or nothing phenomenon

Back 29

Mobitz II block

Front 30

True or False:
In a Mobitz II, the ratio of conducted beats to nonconducted beats varies and is rarely constant.

Back 30

True.

Front 31

Diagnosis of this block requires the presence of a dropped beat without progressive lengthening of the PR interval.

Back 31

Mobitz II block

Front 32

On EKG, it is impossible to make the distinction between an Mobitz I and II at what P-to-QRS ration?

Back 32

2:1

(impossible to see whether progressive lengthening is occurring)

Front 33

A cardiologist might be able to localize the site of a 2:1 Mobitz by using this method.

Back 33

His bundle electrocardiography
(EPS - involves inserting electrodes into the heart)

Front 34

"ultimate heart block"

Back 34

third degree AV block

Front 35

no atrial impulses make it through to the ventricles

Back 35

third degree AV block

Front 36

"complete heart block"

Back 36

third degree AV block

Front 37

usual site of third degree AV block

Back 37

at the AV node or lower

Front 38

How do the ventricles generally respond to a complete heart block?

Back 38

30-45 bpm
idioventricular escape
(usually inadequate)

Front 39

block in which the atria and ventricles have virtually nothing to do with each other

Back 39

third degree AV block

Front 40

block in which the atria and ventricles are separated by the abcolute barrier of a complete conduction block

Back 40

third degree AV block

Front 41

term for any circumstance in which the atria and ventricles are being driven by independent pacemakers

Back 41

AV dissociation

Front 42

P waves and QRS complexes appear at regular intervals, but have nothing to do with each other

Back 42

third degree AV block
(AV dissociation)

Front 43

True or False:
Suppressing the "PVC-looking" beats of a ventricular escape rhythm could be fatal.

Back 43

True

Front 44

Main difference between PVCs and ventricular escape

Back 44

PVC = premature intrusion beat
Escape = delayed/rescue beat

Front 45

True or False:
Ventricular escape is always slower than normal beats.

Back 45

True.

Front 46

Diagnosis of this block requires the presence of AV dissociation in which the ventricular rate is slower than the sinus or atrial rate.

Back 46

third-degree AV block

Front 47

Rhythm that may drive the heart if AV dissociation occurs high in the AV node.

Back 47

accelerated junctional

Front 48

True or False:
Pacemakers are virtually always required when a third degree heart block developes.

Back 48

True.
The ventricular escape is rarely adequate.

Front 49

True or False:
Pacemakers are rarely required for AV dissociation that occurs high enough in the AV node to produce a junctional escape.

Back 49

True.
In this case, an accelerated junctional rhythm usually developes at a rate sufficient to adequately drive the heart.

Front 50

Name the two situations in which high AV dissociation with a junctional escape most often occur.

Back 50

(1) acute infarction
(2) antiarrhythmic overdose

Front 51

What is the leading cause of third-degree heart block?

Back 51

degenerative disease of the conduction system

(may also complicate and AMI)

Front 52

What EKG observation technique is used to diagnose AV blocks?

Back 52

examining the relationship between the P waves and the QRS complexes

Front 53

True or False:
Different degrees of AV block can coexist in the same patient.

Back 53

True.

Front 54

True or False:
Blocks are virtually always permanent phenomenon.

Back 54

False.
Blocks can be transient.

Front 55

a conduction block in either the left or right bundle branches

Back 55

bundle branch block

Front 56

the most efficient means of dispersing the electrical current through the ventricles

Back 56

bundle branches

Front 57

normal duration of QRS complex when conduction flows through the bundle branches

Back 57

less than 0.1 seconds

Front 58

With this type of block, electrical axis deviates and QRS complex widens.

Back 58

bundle branch block

Front 59

block that is diagnosed by looking at the width and configuration of the QRS complexes

Back 59

bundle branch block

Front 60

This block is characterized by an obstruction in right bundle branch conduction.

Back 60

right bundle branch block

Front 61

block characterized by delayed right ventricular depolarization

Back 61

right bundle branch block

Front 62

block in which right ventricular depolarization does not begin until the left ventricle is almost fully depolarized

Back 62

right bundle branch block

Front 63

A bundle branch block is generally characterized by a QRS complex that widens to beyond what duration?

Back 63

0.12 seconds

Front 64

The QRS complex of a right bundle branch block assumes a unique, virtually diagnostic shape in which leads?

Back 64

V1, V2

Front 65

Describe the electrical axis in a right bundle branch block.

Back 65

sharply toward the right

Front 66

RSR in leads V1 and V2 indicate what type of block?

Back 66

right bundle branch block

Front 67

R-prime in leads V1 and V2 indicate what type of block?

Back 67

right bundle branch block

Front 68

What do "rabbit ears" in V1 and V2 indicate?

Back 68

right bundle branch block

Front 69

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.

Back 69

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.

Front 70

In right bundle branch block, in which leads are reciprocal, late deep S waves inscribed.

Back 70

I, AVL, V5, V6
(left lateral leads)

Front 71

What phenomenon occurs in the left lateral leads in cases of right bundle branch block?

Back 71

reciprocal changes

Front 72

How are bundle branch blocks diagnosed on EKG?

Back 72

by looking at the width and configuration of QRS complexes

Front 73

criteria for right bundle branch block

Back 73

(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

Front 74

block characterized by delayed left ventricular depolarization

Back 74

left bundle branch block

Front 75

Left bundle branch block is characterized by a characteristic change in the shape of QRS complexes in which leads?

Back 75

I, AVL, V5, V6

Front 76

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.

Back 76

left bundle branch block

Front 77

block that causes already tall R waves in left lateral leads to become markedly prolonged and broad or notched.

Back 77

left bundle branch block

Front 78

True or False:
"Rabbit Ears" in left bundle branch block are less commonly seen than they are in right bundle branch block.

Back 78

True.

Front 79

In left bundle branch block, what type of changes are seen in the leads overlying the right ventrical?

Back 79

reciprocal changes,
broad and deep S waves

Front 80

True or False:
Left axis deviation is never present in left bundle branch blocks.

Back 80

False.
Left ventrical is so dominant in left bundle branch blocks that left axis deviation may be present, but this is variable.

Front 81

True or False:
Repolarization changes are associated with left bundle branch block, but not right.

Back 81

False.
In both right and left bundle branch block, the repolarization sequence is affected.

Front 82

What repolarization changes may be associated with bundle branch blocks in overlying leads.

Back 82

ST depression
T wave inversion

Front 83

Which leads will show repolarization abnormalities in right bundle branch block?

Back 83

right precordial leads

Front 84

Which leads will show repolarization abnormalities in left bundle branch block?

Back 84

left lateral leads

Front 85

True or False:
Right bundle branch block is a fairly common phenomenon in otherwise normal hearts.

Back 85

True.

Front 86

True or False:
Right bundle branch block can be caused by diseases of the conduction system.

Back 86

True.

Front 87

True or False:
Left bundle branch blocks frequently occur in normal hearts.

Back 87

False.
They almost never occur in normal hearts and almost always reflect significant underlying cardiac disease.

Front 88

Name two diseases that may manifest in a left bundle branch block.

Back 88

degenerative disease of the conduction system
ischemic coronary artery disease

Front 89

True or False:
Bundle branch blocks, once identified, are generally permanent and persistent phenomena that will always appear on EKG.

Back 89

False:
Both right and left bundle branch blocks can be intermittent or fixed.

Front 90

In some individuals, a bundle branch block only appears when a particular heart rate, called ________, is achieved.

Back 90

the critical rate

Front 91

The development of a rate related bundle branch block is directly related to what factor?

Back 91

the time it takes for a particular bundle branch to repolarize

Front 92

the four criteria for left bundle branch block

Back 92

(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.

Front 93

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.

Back 93

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.

Front 94

True or False:
Left bundle branch block may lead to a diagnosis of myocardial infarction.

Back 94

False.
EKG diagnosis of a myocardial infarction cannot be made in the presence of a left bundle branch block.

Front 95

Term used to refer to a conduction block of just one of the fascicles of the left bundle branch.

Back 95

hemiblock

Front 96

True or False:
It is possible for just one fascicle of the right bundle branch to be blocked.

Back 96

False.
The right bundle branch does not divide into fascicles.

Front 97

Name the major effect that hemiblocks have on the EKG.

Back 97

Axis deviation.

Front 98

block in which conduction down the anterior fascicle of the left ventricle is blocked

Back 98

left anterior hemiblock

Front 99

hemiblock in which all the current rushes down the left posterior fascicle to the inferior surface of the heart

Back 99

left anterior hemiblock

Front 100

block characterized by left ventricular depolarization that progresses in an inferior-to-superior and right-to-left direction

Back 100

left anterior hemiblock

Front 101

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.

Back 101

left anterior hemiblock

Front 102

hemiblock characterized by left axis deviation in which the electrical axis of ventricular depolarization is redirected between -30 and -90 degrees.

Back 102

left anterior hemiblock

Front 103

hemiblock characterized by a positive QRS in lead I and a negative QRS in AVF

Back 103

left anterior hemiblock

Front 104

In left anterior hemiblock, if the QRS in lead II is negative, then the axis must lie more negative than _____.

Back 104

negative 30 degrees

Front 105

a block characterized as "the reverse" of left anterior hemiblock

Back 105

left posterior hemiblock

Front 106

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

Back 106

left posterior hemiblock

Front 107

hemiblock in which the axis of depolarization is directed downward and rightward

Back 107

left posterior hemiblock

Front 108

hemiblock in which tall R waves are written inferiorly and deep S wave are seen in the left lateral leads

Back 108

left posterior hemiblock

Front 109

hemiblock characterized by right axis deviation

Back 109

left posterior hemiblock

Front 110

What degree of QRS widening is seen in hemiblock?

Back 110

Very minor to none.
QRS is basically normal.

Front 111

What repolarization abnormalities are characteristic of hemiblocks?

Back 111

None. There are no ST segment and T wave changes.

Front 112

Between left anterior and posterior hemiblocks, which of the two is more common?

Back 112

left anterior hemiblock

Front 113

What is one possible reason that left anterior hemiblock is seen more commonly that left posterior hemiblock?

Back 113

The anterior fascicle is longer and thinner and has a more tenuous blood supply than the posterior fascicle.

Front 114

True or false:
Left anterior hemiblocks are seen in both normal and diseased hearts.

Back 114

True

Front 115

True or false:
Left posterior hemiblocks is seen in both normal and diseased hearts.

Back 115

False.
Left posterior hemiblocks are seen almost exclusively in sick hearts.

Front 116

How is hemiblock diagnosed?

Back 116

by looking for left or right axis deviation

Front 117

criteria for left anterior hemiblock

Back 117

(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

Front 118

criteria for left posterior hemiblock

Back 118

(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

Front 119

True or False:
A bundle branch block and a hemiblock can occur together.

Back 119

True.
A right bundle branch block and a hemiblock can occur together.

Front 120

term that refers to the combination of either a left anterior or left posterior hemiblock with right bundle branch block

Back 120

bifascicular block

Front 121

In bifascicular block, what supplies current to the bulk of both ventricles?

Back 121

Only one fascicle of the left bundle branch

Front 122

Criteria for bifascicular block (with left anterior hemiblock)

Back 122

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

Front 123

Criteria for bifascicular block (with left posterior hemiblock)

Back 123

Right bundle branch block
(1) QRS wider than 0.12 seconds
(2) RSR in V1 and V2

Left anterior hemiblock
(3) Right axis deviation

Front 124

early type of pacemaker capable of firing only at a single predetermined rate

Back 124

fixed rate pacemakers

Front 125

modern pacemaker that fires only when the patient's own intrinsic heart rate falls below a certain level

Back 125

demand pacemakers

Front 126

type of pacemaker in which electrodes are placed into an atrium or ventricle

Back 126

single-chamber pacemaker

Front 127

type of packemaker in which electrodes are placed in both the an atrium and a ventricle

Back 127

dual-chamber pacemaker
(AV sequential pacemaker)

Front 128

rhythm device that creates a small spike on EKG when it fires

Back 128

pacemaker

Front 129

describe the EKG appearance of a ventricular pacemaker

Back 129

spike followed by a wide and aberrant QRS, just like a PVC

Front 130

describe the EKG appearance of an atrial pacemaker

Back 130

spike followed by a P wave and a normal QRS complex

Front 131

describe the EKG appearance of a sequential pacemaker

Back 131

two spikes -- one preceding a P wave, and the other proceeding a wide and bizarre QRS

Front 132

True or False:
A pacemaker spike always has the potential to induce a serious arrhythmia.

Back 132

True.
However, this is a rare occurence as long as the electrodes maintain good contact with the heart.

Front 133

True or False:
Patients with left heart failure stand to benefit the most from a pacemaker placed in the right ventricle.

Back 133

False.
Patients with impaired left ventricular function or CHF may not always benefit from right ventricular pacers.

Front 134

True or False:
Right ventricular pacers may actually precipitate an episode of heart failure in patient with impaired left ventricular function.

Back 134

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.

Front 135

What pacing option is available for patients with impaired left ventricular function?

Back 135

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.

Front 136

True or False:
In some patients, a pacemaker spike may be difficult or impossible to see.

Back 136

True.
Always suspect a pacemaker in the presence of wide QRS complexes and left axis deviation. (Question the patient or check for a pacemaker.)

Front 137

For most individuals, if the tracing is normal except for the presence of axis deviation, you can feel reasonably confident that ______ is responsible.

Back 137

hemiblock

Front 138

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 ____).

Back 138

-30

Left Anterior Hemiblock
(LAHB)