AV Blocks And Hemiblocks (Johnston)

Question 1

What are some etiologies of 1st degree AV block?

Answer 1

Atherosclerosis
HTN
Diabetes

Question 2

This type of AV block has a progressive PR interval prolongation prior to dropped QRS and has “grouped beats”. Progressive lengthening results from earlier arrival in relative refractory period of AV conduction and implies impairment of AV conduction. It is transient.

Answer 2

Secondary AV block-Wenckebach (Type I mobitz)

Question 3

What are etiologies of Wenckebach secondary AV blocks?

Answer 3

All those that cause primary AV block
Digitalis toxicity
ISCHEMIC EVENTS (MI-INFERIOR)
Myocarditis

Question 4

This type of AV block may be seen with an inferior AMI, the level of block is at the level of the AV node, and has a narrow QRS complex

Answer 4

2nd degree AV block-Wenckebach (Mobitz I)

Question 5

What are etiologies of 2nd degree AV block-Mobitz type II?

Answer 5

Ischemic heart disease
May be seen with acute ANTERIOR MI
Degeneration of conduction system

Question 6

This type of AV block has a uniform PR interval, a dropped beat (QRS) and the block occurs at the level of Bundle of his, both bundle branches, and fascicular branches. It is progressive/irreversible

These may be seen with ANTERIOR AMI because block is distal to AV node; worse prognosis

Answer 6

2nd degree AV block, Mobitz type II

Question 7

In this type of AV block, the P waves are never related to QRS complexes

Answer 7

Third degree AV block (complete heart block)

Question 8

Describe the QRS and ventricular rate in 3rd degree heart block at the junctional focus:

Answer 8

Narrow QRS

Ventricular rate 40-60/min

Question 9

Describe the QRS and ventricular rate in 3rd degree AV block at the ventricular focus:

Answer 9

Wide QRS (PVC-like QRS's)
Ventricular rate: 20-40/min

Question 10

What are some etiologies of third degree AV block?

Answer 10

Ischemic
Infiltrative diseases
Cardiac surgery –> BY-PASS, valve replacement, myocarditis, degenerative

Question 11

How do you treat a 3rd degree AV block?

Answer 11

Pacemaker

Question 12

Describe the PR interval in 1st degree AV block:

Answer 12

Increases consistently

Question 13

Describe the PR interval in Wenckebach (2nd degree type 1)

Answer 13

Progressively increases

Question 14

In which AV blocks do you have P waves without a QRS response?

Answer 14

Wenckebach and Mobitz type 2

3rd degree AV block

Question 15

How long is the PR interval in a 1st degree AV block?

Answer 15

> 0.20 seconds