Heart Block

Question 1

What is first degree heart block?

Answer 1

-delayed Atrioventricular conduction through the AV node.
- Despite this every atrial impulse -> ventricular contraction
- therefore every P wave-> QRS complex
- ECG PR interval greater than 0.20 seconds

Question 2

What is second degree heart block ?

Answer 2

-some atrial impulses do not make it through the AV node to the ventricles
-Therefore sometimes P waves do not lead to QRS complexes

Question 3

What is Wenckebach’s phenomenon (Mobitz Type 1) secondary heart block?

Answer 3

• atrial imputes becomes gradually weaker until it does not pass through the AV node.
• After failing to stimulate a ventricular contraction the atrial impulse returns to being strong. This cycle then repeats.
• ECG this will show up as an increasing PR interval until the P wave no longer conducts to ventricles. This culminates in absent QRS complex after a P wave. The PR interval then returns to normal but progressively becomes longer again until another QRS complex is missed.

Question 4

What is mobitz type 2 (secondary heart block)?

Answer 4

• failure or interruption of AV conduction
• missing QRS complexes
• PR interval remains normal
• Risk of asystole

Question 5

What is a 2:1 block (secondary heart block)?

Answer 5

-2 p waves for each QRS
-Every second P wave is not strong enough atrial impulse to stimulate QRS complex.

Question 6

What is third degree heart block?

Answer 6

• complete heart block
• no relationship between P and QRS
• significant risk of asystole

Question 7

Treatment for heart block?

Answer 7

stable - observe
unstable, risk of asystole- First line atropine 500mcg IV

Second line:
Atropine 500mcg IV repeated (up to 6 doses for a total to 3mg)
Other inotropes (such as noradrenalin)
Transcutaneous cardiac pacing (using a defibrillator)

Mobitz type 2 or complete heart block: permanent pacemaker or temporary transvenous cardiac pacing