AV Blocks - EKGs

Question 1

An AV blocks causes what on the EKG?

Answer 1

Missing or delayed QRS following a normal P wave

Question 2

1º AV Block - EKG

Answer 2

• Sinus rhythm
• Uniform PR delay each time
• PR interval > 0.2 sec (1 big box)

Question 3

How to measure PR interval?

Answer 3

Start of P to start of QRS

Question 4

Most common cause of 1º AV block

Answer 4

Atherosclerosis (ischemia) –> conduction degeneration/fibrosis

Question 5

List the first 9 big boxes for calculating HR

Answer 5

300, 150, 100, 75, 60, 50, 43, 38, 33

Question 6

Diagnosing low QRS voltage

Answer 6

Average total height of QRS in 1,2,3

Question 7

Causes of low QRS voltage

Answer 7

Hypothyroid, chronic COPD, pericardial effusion, obesity, amyloid deposit

Question 8

Leads to look for infarctions (ST depressions/elevations)

Answer 8

2, 3, F = inferior wall (RCA)
1, L = lateral wall (LCX)
V1-V6 = septum/apex (LAD)

Question 9

AV block would most likely be associated with which type of infarction? Why?

Answer 9

Posterior/inferior wall (RCA) - 2, 3, AVF

- LOCATION OF CONDUCTION SYSTEM

Question 10

Primary AV block (via MI) is classically associated with what cardiac change?

Answer 10

Heightened vagal tones –> sinus bradycardia (slow HR)

Question 11

2 types of Secondary AV block

Answer 11

Mobitz 1 (Wenckebach)
Mobitz 2

Question 12

Mobitz 1 (Wenckebach)

Answer 12

• Progressively longer PR-intervals
• Eventually a dropped QRS
• “Grouped beats”

Question 13

How to remember causes of Mobitz 1?

Answer 13

Same causes as 1º AV block

Question 14

A Mobitz 1 (Wenckebach) signifies a problem where?

Answer 14

AV node

Question 15

3 MAIN causes of Wenckebach

Answer 15

• Digitalis toxicity
• Inferior MI
• Myocarditis

Question 16

What causes the eventual dropped beat in Wenckebach?

Answer 16

SA nodal impulse reaches AV node closer and closer after the AV refractory period, until eventually the refractory period causes a dropped beat

Question 17

4:3 Wenckebach

Answer 17

Every 4 P waves = 3 QRS’s (4th one dropped)

Question 18

Causes of Mobitz type 2

Answer 18

• Ischemic heart disease

- ANTERIOR MI (LAD)

Question 19

Mobitz type 2 - EKG

Answer 19

• Uniform PR intervals throughout

- Eventual dropped QRS

Question 20

A Mobitz 2 signifies a problem where?

Answer 20

BELOW the AV node (bundle, BBs, fascicular branches)

Question 21

Progression/prognosis of Mobitz 1 vs. Mobitz 2

Answer 21

1 = transient, ok prognosis
2 = progressive, irreversible, BAD prognosis

Question 22

See dropped QRST beats + ST elevation (precordial leads)

Answer 22

Anterior MI –> Mobitz type 2 2º AV block

Question 23

“Escape rhythm”, QRS, rate in Mobitz 1 vs. Mobitz 2

Answer 23

Mobitz 1 – Junctional, narrow QRS, adequate rate

Mobitz 2 – Ventricular, wide QRS, inadequate rate

Question 24

3º AV block - EKG

Answer 24

• Independent atrial and ventricular rates (A-V dissociation)
• Count p wave rate vs. QRS wave rate

Question 25

2 types of 3º AV block

Answer 25

Junctional rhythm (narrow QRS, normal/slow rate)
Ventricular rhythm (wide QRS, too slow rate)

Question 26

Junctional vs. Ventricular rhythms

Answer 26

J = external pacemaker ABOVE the AV node
V = external pacemaker BELOW the AV node

Question 27

Main cause of 3º Heart Block

Answer 27

Ischemia (MI, etc.)

Question 28

How to treat 3º Heart Block?

Answer 28

Pacemaker

Question 29

On EVERY ECG, check what 2 things?

Answer 29

• PR interval (multiple)

- P to QRS relationship