Simple ECG lecture about sinus arrest, sinoatrial exit block, AV block and escape rhythms. Slideshow was made with an audience of medical professionals in mind.

1. Sinus arrest, Sinoatrial exit block,
AV blocks, Escape Rhythms
Dr. Michael-Joseph F. Agbayani, MD FPCP FPCC
@HeartRhythmMD

2. Images used are mine or under a creative commons
license or public domain.

5. SA node: 60 to 100
SA node: 60 to 100
bpm
bpm
AV Junction: 40 to
AV Junction: 40 to
60 bpm
60 bpm
Ventricle: <40 bpm
Ventricle: <40 bpm

8. Sinoatrial Exit Block
• Sinus node still firing
• Impulse fails to conduct beyond SA node
• Degrees
– First degree SA exit block
– Second degree SA exit block (Type 1 and type 2)
– Third degree SA exit block

9. First degree sinoatrial block
• First degree
– Delay in conduction of sinus impulse
– Not evident in a surface ECG

10. Second degree sinoatrial block
• Intermittent failure of the sinus impulse to
exit the node
• Type 1
– Progressive delay in sinus impulse resulting in
non-conducted impulse
– Group beating (Wenckebach periodicity)

11. Second degree sinoatrial block type 1

12. Second-degree sinoatrial block
• Type 2
– Failed conduction of sinus impulse without
progressive prolongation of sinoatrial conduction
time
– Pause is a multiple of baseline P-P interval

14. Third-degree sinoatrial block
• None of the sinus node impulses are able to
exit the node
• Absence of p waves
• Indistinguishable from sinus arrest

15. Sinus Pause / Sinus Arrest
• Sinus node doesn’t fire
• P-P interval of the pause not a multiple of the
baseline P-P interval
• Usually said to be abnormal if > 3 seconds

18. First degree AV block
•
•
•
•
PR interval is > 200 ms and is constant
Each p wave is followed by QRS complex
Marked first degree is >300 ms
May be symptomatic

20. Second Degree AV Block
•
•
•
•
One non-conducted p wave
Mobitz Type 1 (Wenckebach Block)
Mobitz Type 2
2:1 AV block

21. Mobitz Type 1 (Wenckebach)
• Gradual prolongation of PR interval until nonconducted p wave
• RP-PR reciprocity
• Lengthening of the PR interval at progressively
shorter decrements
• Progressively shorter R-R intervals and group beating
• Shortening back to baseline PR interval after the
blocked cycle

24. Mobitz Type 2
• No change in PR before non-conducted P
wave
• Usually associated with His-Purkinje disease

28. 2:1 AV block
• Second degree AV block
• Every other beat is conducted
• PR interval in conducted beats is usually
constant

29. 2:1 AV block
• Classifying into Mobitz Type 1 or type 2 is
discouraged
• Clues to level of block
– Narrow vs wide complex
– Long or short PRs in conducted beats
– PR and RP relationship
– Presence of Mobitz Type 1 block
– Response to Atropine or exercise

30. 2:1 AV block

32. High Grade AV Block
• At least 2 consecutive non-conducted P waves
(3:1 AV Block)
• Also called “advanced second-degree heart
block”
• Look at the PR interval of conducted beats:
should be constant

33. 4:1 AV block

34. 3rd Degree or Complete Heart Block
• None of the P waves are conducted
• P waves and QRS complexes occur
independently of each other
• R-R intervals are usually regular (junctional or
ventricular escape rhythm)

35. SA node: 60 to 100
SA node: 60 to 100
bpm
bpm
AV Junction: 40 to
AV Junction: 40 to
60 bpm
60 bpm
Ventricle: <40 bpm
Ventricle: <40 bpm

37. • R-R intervals are usually regular (escape
rhythm)
• “PR” intervals are not constant / no pattern
• Escape rhythm can be junctional or ventricular

38. Escape Rhythms
• Atrial escape rhythm (<60 bpm)
– P wave morphology abnormal
• Junctional rhythm (40 to 60 bpm)
– Narrow QRS
– Retrograde P waves shortly before or after QRS, if
any
• Ventricular rhythm (<40 bpm)
– Wide, “bizarre” QRS complexes

40. SA node: 60 to 100
SA node: 60 to 100
bpm
bpm
AV Junction: 40 to
AV Junction: 40 to
60 bpm
60 bpm
Ventricle: <40 bpm
Ventricle: <40 bpm

44. Images
•
•
•
•
•
•
•
•
•
•
•
Heart image with conduction system: Public Domain image from Gray’s Anatomy
QRS complex: Public Domain image from Wikipedia user
http://en.wikipedia.org/wiki/User:Agateller
Road Block sign: http://en.wikipedia.org/wiki/File:Road_block.jpg
Traffic: http://en.wikipedia.org/wiki/File:Traffic_jam_on_Phu_Nhuan_district.JPG
Sinoartial exit block: http://commons.wikimedia.org/wiki/User:Jer5150
First degree AV block: http://www.flickr.com/photos/popfossa/
Second Degree AV block Mobitz Type 1:
http://commons.wikimedia.org/wiki/User:Jer5150
Mobitz type 2 and 2:1: http://commons.wikimedia.org/wiki/User:Jer5150
Complete heart block: http://commons.wikimedia.org/wiki/User:Jer5150
Complete heart block strip: http://en.wikipedia.org/wiki/User:MoodyGroove
Junctional rhythm: http://www.flickr.com/photos/nottinghamvets/

45. Images
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•
•
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Sinus pause: http://commons.wikimedia.org/wiki/User:Stevenfruitsmaak
Mobitz Type 1 with escape: Michael Rosengarten BEng, MD.McGill
(ecgpedia.org)
SCT with Pause: Michael Rosengarten BEng, MD.McGill (ecgpedia.org)
Mobitz type 1 and type 2 strips: Munther Homoud, M.D.
(http://ocw.tufts.edu/)
Mobitz Type II: http://lifeinthefastlane.com/author/edward-burns/
High Grade AV block: http://lifeinthefastlane.com/author/edward-burns/
Ventricular Escape rhythm: http://lifeinthefastlane.com/author/edwardburns/
Fixed ratio blocks: http://lifeinthefastlane.com/author/edward-burns/

46. SA exit block, Sinus Arrest, AV Blocks and Escape Rhythms
ECG EXERCISE

56. Images
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•
•
•
•
•
•
•
•
First Degree AV block: http://www.flickr.com/photos/popfossa/
4:1 AV block: http://www.flickr.com/photos/popfossa/
Mobitz type 1: http://www.flickr.com/photos/popfossa/
First Degree AV block: http://www.flickr.com/photos/popfossa/
Type II Sinoatrial exit block: http://lifeinthefastlane.com/author/edward-burns/
Mobitz type 1: http://lifeinthefastlane.com/author/edward-burns/
Complete Heart Block; http://lifeinthefastlane.com/author/edward-burns/
Sinus arrest: http://lifeinthefastlane.com/author/edward-burns/
High grade Av block and Mobitz Type 2:
http://lifeinthefastlane.com/author/edward-burns/

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