Lecture 13- Heart block

Question 1

Atrioventricular Heart block

Answer 1

Delay/failure of conduction of impulses from atria to ventricles via AV node and bundle of His.

Question 2

Causes of heart block:

Answer 2

• Degeneration of electrical conducting system with age (sclerosis and fibrosis)
• Acute MI
• Medications
• Valvular heart disease

Question 3

types of heart block

Answer 3

first degree AV block

Second degree AV block

Third degree AV block

Question 4

first degree AV block

Answer 4

Caused by delayed conduction through the AV node resulting in a consistently prolonged interval

Question 5

features of first degree AV block on ECG

Answer 5

• Slowed without skipped beat (PRI >2s)
• All normal P waves followed by QRS complexes, but PR interval is longer than normal
• Can develop into second or third degree

Question 6

second degree heart block can be divided into

Answer 6

Mobitz type I

Mobitz type II

Question 7

Mobitz type I also known as

Answer 7

Wenkenbach

Question 8

features of second degree Mobitz type I on ECG

Answer 8

PR interval becomes progressively longer until one of the QRS complexes is dropped- PR interval then returns to normal and repeats the cycle

Question 9

feautrs of second degree mobitz type II on ECG

Answer 9

PR interval is normal and constant, but occasionally the P wave is not conducted so a QRS complex is dropped.

Question 10

is mobitz type I or II more dangerous

Answer 10

II

This type of second degree heart block is dangerous as it has a higher chance of progression to third degree heart block (complete)

No prior PR changes

Ventricular rhythm is irregular

Question 11

Third degree AV block

Answer 11

is when there is no impulse transmission between the atria and ventricles and therefore they work independently – no relationships between the P wave and QRS.

Question 12

in third degree AV block the ……. pacemaker takes over (escape rhythm)

Answer 12

Ventricular

Question 13

ventricular pacemaker rate

Answer 13

40bpm

Question 14

atrial rate approx

Answer 14

100bmp

no evidence that any of the atrial impulses are conducted to the ventricles

Question 15

escape rhythms occur when

Answer 15

the conduction system is blocked and so the ventricles have to manage themselves and become their own pacemaker.

Question 16

how does third degree AV block appear on ECG

Answer 16

QRS complex becomes wider because the impulse isn’t travelling via the His-Purkinje system.

Question 17

why is third degree heart block so dangerous

Answer 17

ventricular pacemaker is too slow and the blood pressure cannot be maintained so a proper pacemaker is urgently required for patients with third degree heart block.

Question 18

bundle heart block

Answer 18

Delayed conduction within the bundle branches

Can be:

Right bundle branch block (RBBB)

Left bundle branch block (LBBB)

Question 19

how does bundle branch block appear on ECG

Answer 19

Wide QRS complex (>3 small squares) because ventricular depolarisation takes long