EKG 5: Conduction blocks

Question 1

Define conduction block/ delay

Answer 1

Blocked or delayed conduction of electrical impulses down the conducting system of the heart.

Question 2

AV node Blocks: List and define the 3 degrees

Answer 2

1) First degree: delay
2) Second degree: variable
-a) Type 1: Wenckebach
-b) Type 2
3) Third degree: complete

Question 3

What type of block is diagnosed by examining PR interval & relationship of P waves to the QRS?

Answer 3

AV node blocks

Question 4

First Degree AV Block/delay:
1) What is it?
2) What does it look like on an EKG?
3) What is the P:QRS ratio? Explain

Answer 4

1) Delay in conduction @ the AV node or Bundle of His (EKG cannot differentiate between a block of AV or bundle of HIS
2) EKG: prolonged PR interval (start of atrial depolarization to start of ventricle depolarization)
> 0.2 seconds (> five small boxes)
3) 1:1 P:QRS….every impulse makes it thru the AV node, every QRS complex is preceded by a P wave =- regular rhythm (PtoP & RtoR are regular), narrow QRS

Question 5

First Degree AV Block/delay:
1) Is it common or uncommon?
2) What is the Tx?

Answer 5

1) Common – may be seen in normal hearts or sign of early pathology
2) Usually benign and does not need treatment – except in Lyme disease – see page 201 in your book

Question 6

Describe Second Degree AV Blocks

Answer 6

1) Not every P wave makes it thru AV/His to cause a QRS…….therefore irregular rhythm
2) P to P interval is regular; some p waves are blocked with dropped QRS leading to an irregular R to R interval

Question 7

Describe Mobitz type 1 (Wenckebach block = “wide PR”) 2nd degree AV blocks

Answer 7

-PR interval gradually prolongs (“wide”) with each cycle until one is dropped (“wink” with one eye) and the pattern repeats itself
-Block within AV node – slowed by carotid message/vagal maneuver
-Ratio typically consistent, e.g., 4:3 = 4 p waves, 3 conducted
-Transient and benign, rarely progresses to 3rd degree block

Question 8

Describe Mobitz type 2 second degree AV blocks

Answer 8

1) Dropped beat without progressive lengthening of the PR interval
2) Block below the AV node in His Bundle (minimally affected by carotid message/vagal maneuver)
3) Ratio is often variable - 2:1, 3:2, etc)
4) More serious although less common, may progress to 3rd degree heart block and a pacemaker is indicated for these patients – be ready for complete block

Question 9

Describe a Third Degree AV Block (AKA Complete Heart Block)

Answer 9

-No atrial impulses make it thru to activate the ventricles
-Block at AV node or lower
-Complete dissociation of P waves and QRS complexes
-Atria contract 60-100
-Ventricles contract own pace - Ventricular escape beats……regular rhythm at Ventricular pacer rate
-Slow 30-45/min
-Wide QRS complex
-Pacemaker is treatment