Prerequisite: atrially generated rhythm, with P waves appearing with a regular pattern
Features:
(1) duration of PR interval
(2) number of dropped P wave associated QRS complexes
(3) ratio of P waves to QRS complexes (for second degree AV block)
Types:
(1) first degree AV block
(2) second degree AV block, Mobitz Type I (Wenckebach Phenomenon)
(3) second degree AV block, Mobitz Type II
(4) third degree AV block
|
AV Block
|
PR interval
|
P wave Associated QRS Complex
|
|
first degree
|
> 0.20 seconds
|
none dropped (all conducted)
|
|
second degree, Mobitz I
|
progressively lengthens until QRS dropped, then returns to its shortest interval (variable)
|
intermittent
|
|
second degree, Mobitz II
|
non-varying but often aberrant in appearance
|
intermittent
|
|
third degree
|
NA
|
all dropped (none conducted)
|
In second degree AV blocks the ratio of P waves to QRS complexes refers to the number of P waves preceding a single QRS complex (first degree AV block 1:1; two P waves before 1 QRS complex is 2:1; three P waves before 1 QRS complex is 3:1; etc. ).
