Heart Block

Question 1

what causes an AV nodal block and where?

Answer 1

• functional or structural abnormalities

- AV node itself or His-Purkinje system

Question 2

1/2 cases of AV nodal block are d/t?

Answer 2

fibrosis of conduction system

Question 3

diagnostic criteria for each type of heart block:

• first-degree block

Answer 3

PR interval > 200 ms w/o alterations in HR

Question 4

diagnostic criteria for each type of heart block:

• second-degree block

Answer 4

• intermittent P waves not followed by ventricular complex

- further classified as Mobitz type 1 or type 2

Question 5

diagnostic criteria for each type of heart block:

• third-degree block

Answer 5

• complete absence of CONDUCTED P waves –> P-wave and QRS complex rates differ
• PR interval differs for every QRS complex
• ATRIAL rate is FASTER than ventricular rate

Question 6

what is the MCC of ventricular rates of 30-50 bpm?

Answer 6

third-degree block

Question 7

diagnostic criteria for each type of heart block:

• LBBB

Answer 7

• absent Q waves in leads 1, aVL, and V6
• large, wide, and positive R waves in leads 1, aVL, and V6
• QRS > 120 ms

Question 8

diagnostic criteria for each type of heart block:

• RBBB

Answer 8

• rsR’ pattern in lead V1 (“rabbit ears”)
• wide negative S wave in lead V6
• QRS > 120 ms

Question 9

diagnostic criteria for each type of heart block:

• bifascicular block

Answer 9

• right bundle branch and ONE of fascicle of left bundle branch

Question 10

diagnostic criteria for each type of heart block:

• trifascicular block

Answer 10

• bifascicular block AND prolonged PR interval

Question 11

diagnostic criteria for each type of heart block:

• left ANTerior hemiblock

Answer 11

• LAD
• upright QRS in lead 1
• negative QRS in aVF
• normal QRS duration

Question 12

diagnostic criteria for each type of heart block:

• left POSterior hemiblock

Answer 12

• RAD
• negative QRS in lead 1
• positive QRS in lead aVF
• normal QRS duration

Question 13

second-degree AVB: Mobitz type 1

Answer 13

• constant P-P interval w/ progressively longer PR interval until DROPPED beat

Question 14

significance of second-degree AVB Mobitz type 1

Answer 14

rarely progresses to third-degree heart block

Question 15

second-degree AVB: Mobitz type 2

Answer 15

• usually a/w RBBB or LBBB
• constant PR interval in CONDUCTED beats
• R-R interval CONTAINS the nonconducted (dropped) beat

Question 16

significance of second-degree AVB Mobitz type 2

Answer 16

may precede third-degree heart block

Question 17

initial tx for AVB

Answer 17

correct reversible causes

Question 18

possible causes of AVB

Answer 18

• ischemia
• increased vagal tone
• drugs (digitalis, CCBs, BBs)

Question 19

guidelines for permanent pacemaker implantation

Answer 19

• symptomatic bradycardia w/o reversible cause
• AF w/ 5-second pauses
• complete heart block
• Mobitz type 2 second-degree AVB
• alternating BBB

Question 20

initial tx for hemodynamic compromise caused by bradycardia or heart block

Answer 20

atropine IV and/or TCP or TVP

Question 21

DON’T BE TRICKED

• when should you NOT place a pacemaker

Answer 21

asymptomatic bradycardia in absence of second- or third-degree heart block