ecg lecture: sinus arrest, sinoatrial exit block, av block and escape rhythms

Sinus arrest, Sinoatrial exit block, AV blocks, Escape Rhythms

Dr. Michael-Joseph F. Agbayani, MD FPCP FPCC

@HeartRhythmMD

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

SA node: 60 to 100 bpmSA node: 60 to 100 bpm

AV Junction: 40 to 60 bpmAV Junction: 40 to 60 bpm

Ventricle: <40 bpmVentricle: <40 bpm

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

First degree sinoatrial block

• First degree– Delay in conduction of sinus impulse– Not evident in a surface ECG

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)

Second degree sinoatrial block type 1

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

Third-degree sinoatrial block

• None of the sinus node impulses are able to exit the node

• Absence of p waves• Indistinguishable from sinus arrest

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

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

Second Degree AV Block

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

Mobitz Type 1 (Wenckebach)

• Gradual prolongation of PR interval until non-conducted 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

Mobitz Type 2

• No change in PR before non-conducted P wave

• Usually associated with His-Purkinje disease

2:1 AV block

• Second degree AV block• Every other beat is conducted• PR interval in conducted beats is usually

constant

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

2:1 AV block

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

4:1 AV block

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)

SA node: 60 to 100 bpmSA node: 60 to 100 bpm

AV Junction: 40 to 60 bpmAV Junction: 40 to 60 bpm

Ventricle: <40 bpmVentricle: <40 bpm

• R-R intervals are usually regular (escape rhythm)

• “PR” intervals are not constant / no pattern• Escape rhythm can be junctional or ventricular

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

SA node: 60 to 100 bpmSA node: 60 to 100 bpm

AV Junction: 40 to 60 bpmAV Junction: 40 to 60 bpm

Ventricle: <40 bpmVentricle: <40 bpm

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/

Images• 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/edward-

burns/• Fixed ratio blocks: http://lifeinthefastlane.com/author/edward-burns/

ECG EXERCISESA exit block, Sinus Arrest, AV Blocks and Escape Rhythms

Images• 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/

You are free to:Share — copy and redistribute the material in any medium or formatAdapt — remix, transform, and build upon the materialThe licensor cannot revoke these freedoms as long as you follow the license terms.

This slideshow is under a Attribution-NonCommercial-ShareAlike 4.0 InternationalCreative Commons license.

Under the following terms:Attribution — You must give appropriate credit, provide a link to the license, andindicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.NonCommercial — You may not use the material for commercial purposes.ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original.No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.