Lecture 4: AV blocks Flashcards
Which EKG finding defines a first degree AV block?
PR interval >0.2 sec that is uniform
*0.2 sec = 5 small boxes or 1 large box
Presence of what 4 underlying conditions enhances the chances of a 1st degree AV block?
- Atherosclerosis
- HTN
- Diabetes
- Degeneration of conduction system/fibrosis CHD
What’s the cause of this rhythm?
1st degree AV block
What’s the definition of a sinus rhythm?
Upright ‘P’ waves preceding QRS in lead II
Epigastric pain, GERD, and other upper GI sx’s can be a clue for that cardiac abnormality?
Inferior wall MI
What are the EKG characteristics of a 2nd degree AV block, Mobitz I (Wenckebach)?
i.e., intervals, QRS morphology…
- Narrow QRS
- Progressive PR-interval prolongation until ventricular beat is dropped, sequence is then repeated
- “Grouped beats”
The progressive lengthening of the PR-interval in Mobitz I (Wenckebach) results from what?
Level of the block is where?
- Earlier arrival in relative refractory period of A-V conduction
- Block is at level of AV node
List 4 etiologies which can lead to a 2nd degree AV block, Mobitz I (Wenckebach)?
- All things that cause 1st degree AV block
- Digitalis toxicity
- INFERIOR acute MI
- Myocarditis
Whenever you see “grouped beating” on an EKG strip you should immediately think what?
2nd degree AV block - Mobitz I (Wenckebach)
A 2nd degree AV block, Mobitz Type II may be due to what 3 underlying etiologies?
- Ischemic heart disease
- May be seen with acute ANTERIOR MI
- Degeneration of conduction system (i.e., aging)
What type of acute MI is associated with a 2nd degree AV block, Mobitz Type I and Type 2?
- Type 1 (Wenckebach)= acuteINFERIORMI (sinceRCA supplies at or above AV node)
- Type 2 = acute ANTERIOR MI (since LAD supplies distal conduction system)
What are the characteristic EKG findings of a 2nd degree AV block, Mobitz Type II?
Intervals, QRS…
- Fixed/uniform PR interval
- Occasional dropped beats (QRS) in 2:1, 3:1, or 4:1 pattern
- QRS usually wide (due to block being distal)
A 2nd degree AV block, Mobitz Type II may occur at which 3 levels?
- Bundle of His
- Both bundle branches
- Fascicular branches
What is the progression and tx like for a 2nd degree AV block, Mobitz Type II?
- Progressive/irreversible
- Permanent pacemaker indicated
What is the ECG interpretation?
2nd degree AV block, Mobitz Type II and LBBB
What are the EKG findings associated with a third degree heart block (aka complete block)?
- P waves NEVER related to QRS complexes
- 2 indpendent rhythms (A-V dissociation)
A 3rd degree heart block can occur above or below the AV node and what serves as the escape rhythm for each type and QRS findings?
Ventricular rate?
- Above –> junctional rhythm/ w/ NARROW QRS (rate 40-55)
- Below –> ventricular pacemaker w/ WIDE QRS (rate 20-40)
What are 3 of the major etiologies associated with 3rd degree heart block (aka complete AV block)?
- Ischemic
- Infiltrative diseases
- Cardiac surgery: by-pass/valve replacement, myocarditis, degenerative
How do you treat a 3rd degree AV block?
Permanent pacemaker
How do you interpret this rhythm and how do you treat?
- 1st degree AV block
- Tx: do nothing
When looking at a strip showing a 2:1 AV block which can be caused by either a Mobitz type I or II, what general rule of thumb should be used to distinguish the cause?
- If PR interval is prolonged and QRS is narrow it is likely a type I (Wenckebach)
- If PR interval is normal and QRS is wide it is likely a type II, and pacemaker is warranted
Which technique can be employed at the bedside to get a better look at the root cause of a 2:1 AV block?
Vagal maneuver
How would you interpret this EKG finding?
3rd degree AV block
Interpret this EKG
LBBB w/ 2nd degree AV block, type II
