ICL 2.7: ECG Interpretation

Question 1

what is sinus bradycardia?

Answer 1

sinus rhythm with heart rate < 60 bpm

can be normal in athletes who have a conditioned higher PNS response or it can be in the elderly due to meds

Question 2

what is 1st degree AV block?

Answer 2

block is in the AV node

PR interval is prolonged >120 ms

Question 3

what is 2nd degree AV block?

Answer 3

1. Mobitz type I = Wenkebach

increasingly long PR intervals followed by a dropped QRS complex –> the AV node keeps trying till it’s completely blocked and there’s no conduction to the bundle of His thus no ventricular conduction and you get a P wave of atrial contraction without any ventricle contraction to follow

block is in the AV node

2. Mobitz type II

consistently long PR intervals followed by a dropped WRS complex

block is in the bundle of His

Question 4

what is 3rd degree AV block?

Answer 4

block is below the AV node

there’s no conduction to the ventricles so any QRS comes from bundle of His or lower:
QRS <120 ms then escape is in bundle of His

QRS >120 ms escape is in fascicles below bundle of His

no connection between atria conduction and ventricular conduction = AV disassociation

Question 5

what are the EKG characteristics of a Mobitz type I?

Answer 5

PR gets progressively longer until the AV node completely blocks and there’s no conduction to the Bundle of His so no ventricular conduction = P wave without a QRS complex after

PR interval after the dropped WRS is shorter than the previous PR interval

P to P interval is the same because the SA node and atria depolarize normally

R to R interval shortens because the % increase of PR lengthening decreases

conduction improves with exercise, catecholamines and atropine –> conduction worsens with carotid massage because it slows the AV node

Question 6

what are the EKG characteristics of a Mobitz type II?

Answer 6

it’s caused by the bundle of His suddenly blocking so there’s no PR prolongation prior to sudden block –> then you see a P wave w/o QRS complex after = nonconductor P “dropped beat”

if QRS <120 then it’s an AVN or His bundle block

if QRS >120 ms then there’s a BBB in addition to the AVN or His bundle block

it’s likely to progress to complete heart block permanently so treat with pacemaker

conduction improves with carotid massage and worsens with atropine because the parasympathetic nervous system works on the AV node but not below it

Question 7

what is 2:1 AV block?

Answer 7

it’s when every other beat is dropped so you can’t tell if it’s Mobitz I or II since you can’t see if there is PR interval prolongation

AV node conduction gets faster with exercise so if you put someone on a treadmill you’ll get more complexes and you’ll be able to see if the PR interval is constant or getting longer

Question 8

which conditions are likely to cause type I 2nd degree heart block?

Answer 8

1. acute inferior MI
2. digoxin effect
3. AV blockers
4. elderly
5. post OH surgery
6. myocarditis

Question 9

which conditions are likely to cause type II 2nd degree heart block?

Answer 9

1. acute septal MI

2. conduction fibrosis

Question 10

which conditions are likely to cause 2:1 2nd degree heart block?

Answer 10

1. all MIs

2. conduction fibrosis

Question 11

what are the indications you need a pacemaker?

Answer 11

1. symptomatic bradycardia
2. 2nd degree AVB MII or symptomatic 2:1
3. 3rd degree AVB