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NSCC 7150 > AV Blocks > Flashcards

AV Blocks Flashcards

1
Q

what is a first-degree AV block is characterized by?

A

a delay or interruption of the electrical impulse at the AV node; AV node holds each SA node impulse longer than normal

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2
Q

what will look different on the ECG strip for a first-degree AV block?

A

PRI - will be longer than normal, >0.20 seconds

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3
Q

is first degree AV block its own rhythm?

A

no its an event in an underlying rhythm, so will always be _____ with first degree AV block

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4
Q

O2 supply and demand implications for first-degree AV block

A
  • can be normal
  • affect on CO depends on underlying rhythm (ie. if HR is low, CO is decreased)
  • can generate into a worse AV block
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5
Q

characteristics of 1st degree AV block
- rate
- rhythm
- P wave
- PRI
- QRS complex
- conduction problem

A
  • rate: 60-100bpm
  • rhythm: regular
  • P wave: positive, upright, one before each QRS
  • PRI: prolonged, constant, >0.20 seconds
  • QRS complex: 0.10 sec or less
  • conduction problem: site of impulse formation is the SA node, but there is a delay in conduction at the AV node
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6
Q

causes of first degree AV block

A
  • can be normal
  • drugs (beta blockers, calcium channel blockers)
  • MI
  • lyte imbalances
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7
Q

intervention for first degree AV block

A

Assess the pt (ABCs). Usually patients are asymptomatic, but if HR is <60 and the patient is symptomatic, atropine may be ordered

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8
Q

second degree AV block type 1

A
  • aka 2 AV block Type I, Mobitz Type I, or Wenckebach
  • SA node initiates impulses but AV node progressively delays each subsequent impulse a little longer than preceding one until one is blocked completely or non-conducted
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9
Q

how is the PRI affected in second degree AV block type 1?

A

it lengthens because the AV node progressively delays each subsequent impulse from the SA node until one impulse is not conducted or dropped; long, longer, dropped; will see lengthening PRI then a P wave not followed by a QRS complex

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10
Q

two hallmark characteristics of second degree AV block type 1

A

progressively lengthening PR interval and is cyclical

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11
Q

O2 supply and demand implications for Second-Degree AV Block Type I

A
  • highly dependent on how slow HR is as a result of the dropped QRS complexes
  • even though there is a non-conducted P wave, the lack of a corresponding QRS complex decreases CO as its dependent on ventricular depolarization and contraction
  • potential to generate into a worse AV block
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12
Q

characteristics of second-Degree AV Block Type I
- rate
- rhythm
- P wave
- PRI
- QRS complex

A
  • rate: 60-100bpm (may be lower). atrial > ventricular
  • rhythm: irregular
  • P wave: positive, upright, not all P waves followed by QRS
  • PRI: lengthening until QRS is dropped
  • QRS complex: 0.10 sec or less
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13
Q

conduction problem in second degree av block type 1

A

site of impulse formation is the SA node, but some impulses are blocked from reaching the ventricles. Each impulse take longer and longer to conduct through the AV node until one P wave is not conducted through, resulting in a dropped QRS complex

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14
Q

cause of second degree av block type 1

A
  • Drugs (beta blockers and digoxin)
  • MI (esp r/t right coronary artery conclusion)
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15
Q

intervention for second degree AV block type 1

A

Assess pt (ABCs). Patients may be asymptomatic. If HR (ventricle rate) is below 60 and the patient has symptoms, atropine or temporary pacing may be considered.

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16
Q

second-degree AV block Type II on ECG tracing shows?

A
  1. PRI is fixed and constant, but can be prolonged
  2. P waves are normal looking because they originate from the SA node, but there will be more P waves compared to QRS complexes
  3. ratio of P waves to QRS complexes can vary as number of blocked SA node impulses varies; AV block may not be constant, resulting in periods of normal sinus rhythm interspersed within the AV block
  4. QRS complex of the conducted P waves are normal because they follow the normal conduction pathway
17
Q

where does blocking of impulse occur in second-degree AV block Type II?

A

in the bundle of His or, more commonly, at the level of the bundle branches where there is a complete block at one bundle branch and an intermittent block at the other

18
Q

do you state the ratio in second degree av block type 2?

A

yes; ratio of P waves to QRS complexes

19
Q

O2 supply and demand implications for second-degree AV block Type II

A
  • effect on CO correlates to ventricular rate
  • the more P waves dropped, the slower the ventricular rate becomes = decreasing CO
  • potential to generate into a more complete or third degree heart block
20
Q

characteristics of second-degree AV block Type II
- rate
- rhythm
- P wave
- PRI
- QRS complex

A
  • rate: 60-100bpm (may be lower). atrial > ventricular
  • rhythm: regular
  • P wave: positive, upright, not all Ps followed by QRS
  • PRI: constant when followed by QRS. may be slightly longer than normal
  • QRS complex: 0.10 sec or less
21
Q

conduction problem in second degree AV block type 2

A

site of impulse formation is the SA node, but some impulses are blocked from reaching the ventricles. The block can occur at the bundle of His or at the level of the bundle branches.

22
Q

causes of second degree AV block type 2

A
  • ischemia of bundle branches secondary to decrease O2 supply from a left coronary artery occlusion
  • anterior MI
23
Q

interventions for second degree AV block type 2

A

Assess pt (ABCs). If the ventricle rate drops below 60 and the patient is symptomatic, temporary pacing should be started.

Temporary pacing may be delivered transcutaneously or transvenously.

24
Q

third degree AV block

A
  • aka complete AV or heart block
  • complete and permanent disruption in AV nodal conduction
25
Q

what happens with conduction in third degree heart block?

A
  • all impulses initiated above the ventricles are blocked from reaching the conduction system in the ventricles
  • ventricles are depolarized by a secondary or escape pacemaker in the AV junction below the site of the AV block, or by an escape pacemaker in the ventricles
  • SA node continues to fire even though impulses are blocked
26
Q

what is true about atrial and ventricular depolarization in third degree heart block?

A
  • there is no relationship between atrial and ventricular activity
  • atrial pacemaker (SA node) and ventricular pacemakers operate completely independently (AV dissociation)
  • atrial and ventricular rates will be different but each rhythm will be regular at its own rate
27
Q

AV dissociation produces an ECG tracing that shows?

A
  1. atrial rate tends to be higher than the ventricular rate due to higher intrinsic rate of SA node (60–100 bpm) compared to the intrinsic rate of the AV junction (40–60 bpm) or the Purkinje fibres (20–40 bpm)
  2. lack of a relationship between the P wave and the QRS complex is observed in the PR interval
  3. QRS complexes vary depending on the level of the secondary escape pacemaker (influenced by AV block)
28
Q

where can the complete AV block occur?

A

anywhere from the AV junction down—it may be in the AV node, the bundle of His, or in both bundle branches

29
Q

what if the block is higher up in junctional tissue in third degree?

A

ventricles will be depolarized by a junctional escape pacemaker just below the level of the block, resulting in a QRS complex that is almost normal

30
Q

what if the block occurs lower down in the conduction pathway in third degree?

A

escape pacemaker will also be lower in the conduction system as the escape pacemaker is always below the level of the AV block; will have wide and bizarre–looking QRS complexes

31
Q

why does depolarization from a ventricular escape pacemaker take a longer time?

A

because the electrical impulse has to travel from cell to cell through “ordinary” ventricular tissue

32
Q

how to interpret third degree

A
  1. initially circle all P waves
  2. map out P waves even if you can’t see them clearly - SA node likes to beat regularly so P waves should line up
  3. look for QRS complex or T waves that seem different
33
Q

O2 supply and demand implications for third degree AV block

A
  • slower ventricular rate, leading to decreased CO
  • decreased atrial kick d/t dyssynchrony b/w atria and ventricles depolarization and contraction = decreased preload and CO
34
Q

characteristics of third degree AV block
- rate
- rhythm
- P wave
- PRI
- QRS complex

A
  • rate: atrial > ventricular
  • rhythm: regular for both atria and ventricles but no relationship between both
  • P wave: positive, upright
  • PRI : no true PRI bc different contracting rates b/w atria and ventricles
  • QRS complex: site of ventricle escape pacemaker will determine the shape and length of the QRS complex; farther away from AV node = wider; closer = narrow
35
Q

cause of third degree heart block

A

ischemia or MI

36
Q

intervention for third degree heart block

A
  • check/assess pt (ABCs)
  • if symptomatic, may need atropine, but most likely pt will need pacemaker

NSCC 7150 (11 decks)

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