Heart Blocks

Question 1

First Degree AV Heart Block

Answer 1

Rate: may occur with any sinus rhythm
Rhythm: Regular
P waves: normal; preceding every QRS interval 
PR interval: >0.20
QRS interval: <0.12

“If R is far from P then you have 1st degree”

Question 2

Second Degree AV Block - Mobitz Type I/Wenkebach

Answer 2

Rate: depends on underlying rhythm
Rhythm: usually irregular
P waves: normal; more Ps than QRS complexes
PR interval: progressive lengthening until blocked/dropped QRS complex
QRS complex: <0.12

“longer, longer, longer, drop then you have a Wenkebach”

Question 3

Second Degree AV Block - Mobitz Type II

lethal rhythm

Answer 3

Rate: atrial rate is faster than ventricular rate
Rhythm: Irregular
P waves: intermittent conduction; more Ps than QRS complexes
PR interval: consistent PR interval for conducted beats
QRS complex: may be wider than normal

“if some Ps don’t get through then you have Mobitz II”
(PR intervals are the same when P waves present)

Question 4

Third Degree AV Block - Complete Heart Block

Answer 4

Rate: atrial usually normal, ventricular <40 or junctional >40
Rhythm: usually regular, but dissociated (Ps march out and QRS complexes march out)
P waves: normal; not related to QRS complexes; more P waves than QRS complexes
PR interval: none or all look different
QRS interval: depends on level of escape rhythm

“if Ps and Qs don’t agree then you have third degree”