Conduction Blocks

Question 1

1. Discuss some major and important things to observe when methodically reviewing an EKG.

Answer 1

P wave: rate and is it upright
P to QRS relationship: ratio 1:1, Pwave precedes each QRS
PR interval less than 0.12-.2sec
QRS narrow <0.12

Question 2

1. Narrow QRS suggests what origin of rhythm?

Answer 2

super ventricular focus, widening with ventricular focus or SV with bundle block

Question 3

Inverted P wave could be do to what? What if you have too many P waves

Answer 3

junctional or atrial focus

additional P waves signal some AVN conduction problem

Question 4

What leads are Pwaves best observed in?

Answer 4

lead II and V1

Question 5

1. What is junctional escape?

Answer 5

during SAN arrest, rhythm is taken over by AV node, this can deteriorate into ventricular escape (worse)

Question 6

What is a retrograde Pwave?

Answer 6

a P wave that is delivered by the AV and as such occurs after the QRS wave

Question 7

1. How can you tell the difference between junctional and ventricular escape?

Answer 7

ventricular rates are slower and have a wider QRS generally speaking

Question 8

Name 2 distinct features of junctional escape.

Answer 8

no P-wave preceding QRS
slow, regular, narrow QRS

(note: can be dangerous- can lead to syncope)

Question 9

1. Describe the characteristic of 1st degree AVB.

Answer 9

long PR interval >210, still one p-wave for each QRS

Question 10

1. Describe the characteristic of 2nd degree AVB, type I v. type II.

Answer 10

intermittent lack of AV conduction
type I has lengthening of PR interval before dropping
type II has consistent PR interval and random dropping

types are difficult to distinguish when beats are 2:1

Question 11

1. Describe the characteristics of 3rd degree AVB.

Answer 11

complete electrical disconnect of atria and ventricles

observe separate disconnected rhythms

Question 12

2. What are some possible causes of 1st degree AVB.

Answer 12

degenerative fibrosis,
inflammation or infiltration of cardiomyocytes
drug related (digoxin, B-blocker and Ca++ blockers)
high vagal tone (normal in athletes)

additionally drugs and electrolyte imbalance

Question 13

3. What is “high grade” AV block?

Answer 13

more than one blocked P wave in a row, although PR interval is maintained when conducts, intermediate severity between 2nd and 3rd degree

AV node is not able to recover and conduct after one missed beat

Question 14

How are intra cardiac recording useful?

Answer 14

.

Question 15

3. What are possible causes of Type II 2ndary block?

Answer 15

a more ominous clinical sign, can easily progress to 3rd degree block, which has the potential to be fatal, can because by ischemia or infection (reversible)

Question 16

2. Electrically speaking, what is apparent of a bundle branch blockage?

Answer 16

blockage of the purkinje fiber conduction causes one side to move more slowly than the other

causes widening of the QRS complex

Question 17

In BBB the late activation occurs where?

Answer 17

toward the direction of the block

ie. LBBB, late positive V6, late negative V1
RBBB, late positive V1 (rabbit ears) and late negative V6, I and aVL

Question 18

What is diagnostic of a RBBB?

Answer 18

prolonged QRS complex
rSr’ or rSR’ with inverted T in leads V1-V2

broad S in leads I, aVL and V5-V6

Question 19

What is diagnostic of LBBB?

Answer 19

prolonged QRS complex >120
QS waves in leads V1-3
notched or broad R waves
no Q waves and ST-T abnormalities in leads I, aVL, V6